For Peer Review Only 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

IUPAC

Glossary of Methods and Terms used in Analytical Spectroscopy

Journal: Pure and Applied Chemistry

ManuscriptFor ID PeerPAC-REC-19-02-03.R2 Review Only

Manuscript Type: Recommendation

Date Submitted by the 14-Sep-2019 Author:

Complete List of Authors: Goenaga-Infante, Heidi; LGC Limited, Warren, John ; LGC Ltd Chalmers, John; Infrared and Raman Discussion Group, UK Dent, Geoffrey; Infrared and Raman Discussion Group, UK Todoli, Jose; Universitat d'Alacant, Department of Analytical Chemistry Collingwood, Joanna; University of Warwick, School of Engineering Telling, Neil; Keele University , Institute for Science and Technology in Medicine Resano, Martin; Universidad de Zaragoza, Department of Chemistry Limbeck, Andreas; Technische Universitat Wien, Institute of Chemical Technologies and Analytics Schoenberger, Torsten; Bundeskriminalamt Hibbert, David; UNSW Sydney, School of Chemistry Le Gresley, Adam; Kingston University Adams, Kristie; Steelyard Analytics Craston, Derek; LGC Ltd

analytical spectroscopy, nuclear magnetic resonance, atomic Keywords: spectroscopy, molecular spectroscopy, infrared spectroscopy, Raman spectroscopy

Author-Supplied Keywords:

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1 2 3 4 5 Glossary of Methods and Terms used 6 7 in Analytical Spectroscopy (IUPAC 8 9 10 Recommendations 2019) 11 12 13 14 Prepared for publication by: 15 Heidi Goenaga Infante1, John Warren1, John Chalmers2, Geoffrey Dent2, Jose Luis 16 Todoli3, Joanna Collingwood4, Neil Telling5, Martin Resano6, Andreas Limbeck7, 17 Torsten SchoenbergerFor Peer8, D Brynn HibbertReview9, Adam LeGresley Only10, Kristie Adams 11, Derek 18 Craston1 19 20 21 1 22 LGC Limited, Teddington, United Kingdom 23 2 Infrared and Raman Discussion Group, UK 24 3 Department of Analytical Chemistry, University of Alicante, Alicante, Spain 25 4 School of Engineering, University of Warwick, Coventry, UK 26 5 Institute for Science and Technology in Medicine, Keele University, Stoke on Trent, 27 28 UK 6 29 Department of Analytical Chemistry, University of Zaragoza, Zaragoza, Spain 30 7 Institute of Chemical Technologies and Analytics, TU Wien, Austria 31 8 Bundeskriminalamt Wiesbaden, Germany 32 9 School of Chemistry, UNSW Sydney, Sydney, Australia 33 10 Kingston University, United Kingdom 34 11 Steelyard Analytics, Manassas, USA 35 36 37 38 39 40 41 42 43 44 45 This work was prepared under the project 2017-027-1-500: Spectroscopic methods of 46 analysis (chapter 5 of the IUPAC Orange Book) under task group Chair Derek Craston 47 and membership John Chalmers, Joanna Collingwood, Geoffrey Dent, Heidi 48 Goenaga-Infante, Adam LeGresley, Andreas Limbeck, Martin Resano, Torsten 49 Schoenberger, Jose Luis Todoli, Neil Telling and John Warren, 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 ABSTRACT 4 5 6 Recommendations are given concerning the terminology of concepts and methods used 7 in spectroscopy in analytical chemistry, covering nuclear magnetic resonance 8 spectroscopy, atomic spectroscopy and molecular spectroscopy. 9 10 11 KEYWORDS 12 13 14 analytical spectroscopy, nuclear magnetic resonance, atomic spectroscopy, molecular 15 spectroscopy, infrared, Raman. 16 17 18 For Peer Review Only 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 Contents 4 5 Abstract ...... 2 6 7 Keywords ...... 2 8 9 Introduction...... 4 10 11 General Terms...... 6 12 13 NMR Spectroscopy ...... 40 14 15 Atomic Spectroscopy...... 75 16 17 Molecular Spectroscopy ...... 104 18 For Peer Review Only 19 Index of symbols and abbreviations ...... 142 20 21 Acknowledgments...... 147 22 23 Membership of sponsoring bodies...... 148 24 25 References ...... 148 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 INTRODUCTION 4 5 6 Spectroscopy is a study of the interaction between matter and electromagnetic 7 radiation. 8 The origins of spectroscopy began with the study of visible light, most notably the 9 fundamental studies of crude spectra of sunlight by Isaac Newton in 1672 but the term 10 has expanded its definition to cover the analysis of spectra covering the entire range of 11 the electromagnetic spectrum. This vast frequency range correlates to an equally wide 12 13 range of energy transitions required to allow the absorption and emission of 14 electromagnetic radiation. The term spectroscopy therefore encompasses a range of 15 disparate techniques covering phenomena including nuclear disintegration, excitation of 16 electrons and molecular vibrations and rotations. These can all give valuable qualitative 17 and quantitativeFor information Peer about Review the physical and chemicalOnly properties of materials 18 and summarized in Table 1. 19 20 21 22 Table 1: Regions of the electromagnetic spectrum. 23 Spectral Approximate Energy transitions Analytical techniques 24 region wavelength studied in matter (spectroscopy) 25 (wavenumber) range 26 27 28 Gamma 1–100 pm Nuclear transitions Gamma-ray 29 and disintegrations 30 X-ray 6 pm–100 nm Ionization by inner X-ray; X-ray 31 electron removal fluorescence 32 Vacuum 10–200 nm Ionization by outer 33 ultraviolet electron removal 34 35 Ultraviolet 200–400 nm Excitation of UV-VIS 36 valence electrons 37 Visible 400–780 nm Excitation of UV-VIS 38 valence electrons 39 Near-infrared 780 nm – 2.5 μm Excitation of Near-IR 40 (12 800 – 4000 cm–1) valence electrons; 41 42 molecular 43 vibrational 44 overtones 45 Mid-Infrared 2.5 – 25 μm Molecular Infrared (IR) 46 (4 000 – 400 cm–1) vibrations: spectroscopy, Raman 47 stretching, bending, spectroscopy 48 and rocking 49 50 Far-infrared 25 – 1000 μm Molecular rotations Far-IR, Terahertz 51 (400 – 10 cm–1) spectroscopy 52 Microwave 0.1 – 30 cm Molecular rotations electron spin 53 and electron spin resonance, microwave 54 spectroscopy 55 −1 3 56 Radio- 10 – 10 m Molecular rotations nuclear magnetic 57 frequency and nuclear spin resonance 58 59 Spectroscopy, spectrometry, spectrophotometry and spectrography are terms used to 60 refer to the measurement of radiation intensity as a function of frequency or wavelength

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1 2 3 and are often used to describe experimental spectroscopic methods. Spectral measuring 4 instruments [VIM 3.1] are referred to as spectrometers, spectrophotometers, 5 6 spectrographs or spectral analyzers. 7 Spectroscopic methods in Analytical Chemistry involve measurements of the frequency 8 and intensity of electromagnetic radiation emitted, absorbed or reflected as a 9 consequence of transitions between different energy states within the nucleus, atom or 10 molecule. The output of a spectrometer is referred to as a spectrum and can be used for 11 both qualitative and quantitative purposes. 12 Following VIM [1] and present IUPAC format, the concept entries of these 13 14 Recommendations provide term(s), definition and explanations by examples and notes. 15 Additionally, the document the information is taken from is stated as "Source" using 16 the respective reference number (e.g. [2] for the third edition of the Orange Book). 17 Within a givenFor entry, Peerterms referring Review to other concepts Only defined in these 18 Recommendations appear in italics on first use. The same holds for VIM terms, 19 however these are marked with the VIM entry number, e.g. measurement principle 20 21 [VIM 2.4], because the definition is not reproduced here. 22 Fundamental terms are taken from the Green Book [3], and other IUPAC 23 Recommendations with no change or with minor changes in formatting. 24 These Recommendations are limited to three basic forms of spectroscopy used in 25 analytical chemistry namely, nuclear magnetic resonance, molecular spectroscopy and 26 atomic spectroscopy. Other techniques are either discussed elsewhere (e.g. UV in 27 Chromatography) or fall outside the scope of this edition of the Orange Book. 28 29 30 31 1. atomic spectroscopy 32 33 Measurement principle [VIM 2.4] of spectroscopy for the study of electromagnetic 34 radiation absorbed and emitted by atoms. 35 36 37 Note: Atomic spectra may be emission or absorption spectra. 38 39 2. molecular spectroscopy 40 41 Measurement principle [VIM 2.4] of spectroscopy for the study of rotational, 42 vibrational and electronic transitions of molecules. 43 44 45 Note: Molecular spectra may be emission or absorption spectra. 46 47 3. nuclear magnetic resonance spectroscopy, (NMR) 48 49 Measurement principle [VIM 2.4] of spectroscopy to measure the precession of 50 magnetic moments placed in a magnetic induction based on absorption of 51 52 electromagnetic radiation of a specific frequency by an atomic nucleus. 53 54 Note 1: Nuclei having a suitable magnetic moment include 1H, 13C, 15N, 19F, 31P. 55 56 Note 2: The technique is used as a method of determining structure of organic 57 molecules, or as a mechanism for quantification 58 59 60 Source: [4].

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1 2 3 4. spectrometry 4 5 6 Measurement of quantities related to electromagnetic radiation or charged particles as a 7 means of obtaining information about a system and its components. 8 9 Examples: electron emission spectrometry, mass spectrometry. 10 11 Source: [5] p 1738. See also: spectroscopy. 12 13 14 5. spectroscopy 15 16 Study of chemical systems by the electromagnetic radiation with which they interact or 17 that they produce. 18 For Peer Review Only 19 Examples: atomic absorption spectroscopy, nuclear magnetic resonance spectroscopy. 20 21 22 Source: [5] p 1738. See also: spectrometry. 23 24 GENERAL TERMS 25 26 Fundamental terms defined here are from the IUPAC Green Book (3rd edition) [3] and 27 28 “Handbook of vibrational spectroscopy” [6]. 29 30 6. absorbance, A 31 deprecated: extinction 32 obsolete: attenuance 33 34 Logarithm of the division of incident radiant power (P ) by transmitted radiant power 35 0 36 (Ptr). 37 A = log(P0/Ptr) = –log (T) = –log(1 – αi), where T is the transmittance and αi is the 38 absorptance. 39 40 Note 1: The base of the logarithm should be specified. See decadic absorbance, 41 (log , lg), and Napierian absorbance (ln). 42 10 43 44 Note 2: Although the term absorbance used by chemists often means the decadic 45 absorbance as measured (See experimental absorbance), the data must be 46 corrected for reflection, scattering and luminescence if absorbance is to 47 have absolute numerical significance. 48 49 Note 4: Confusingly, the term absorbance is also widely used for the negative 50 51 logarithm of the ratio of the final to the incident intensities of processes 52 other than transmission, such as attenuated total reflection and diffuse 53 reflection. 54 55 Source: [3] p 36. See also: internal absorbance. 56 57 58 7. absorptance, α 59 absorption factor 60

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1 2 3 Absorbed radiant power (P ) divided by incident radiant power (P ). α = P /P 4 abs 0 abs 0 5 6 Source: [3] p 36. 7 8 8. absorption coefficient 9 10 See: linear decadic absorption coefficient, linear Napierian absorption coefficient, 11 molar decadic absorption coefficient, molar Napierian absorption coefficient. 12 13 14 9. absorption index, k 15 imaginary refractive index 16 17 Imaginary partFor of the Peercomplex refractive Review index describing Only absorption of 18 electromagnetic radiation. 19 20 21 Source: [3] p 37. 22 23 10. absorption spectrum 24 25 General term for the spectrum of electromagnetic radiation absorbed by a sample. 26 27 28 Note 1: The ordinate quantity may be absorption cross-section, absorption 29 coefficient or absorbance. 30 31 Note2: If the ordinate quantity is the absorbance, but not otherwise, the spectrum 32 may be called an absorbance spectrum. 33 34 35 Source: [6]. 36 37 11. accidental degeneracy 38 39 Condition that occurs when two or more normal transitions have the same energy as a 40 matter of coincidence, as opposed to because of symmetry conditions. 41 42 43 Source: [6]. 44 45 12. aliasing 46 47 See: folding (in spectroscopy). 48 49 50 13. angle of incidence, θ 51 52 Angle between a beam of electromagnetic radiation and a line normal to a surface. 53 54 55 56 57 58 59 60

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1 2 3 4 5 6 7 8 9 normal 10 11 12 13 14 15 16 17 14. anisotropicFor Peer Review Only 18 nonisotropic 19 20 21 Having properties that depend on direction. 22 23 Source: [7] p 2198. See also: isotropic. 24 25 15. apodization 26 27 28 Technical term for changing the shape of a mathematical function, an electrical signal 29 or an optical transmission, to remove or smooth a discontinuity at the edges, literally 30 meaning ‘removing the foot’. 31 32 Note 1: Originally ‘apodization’ describes the procedure by which Fourier- 33 transform infrared spectra are corrected for the side lobes that appear in the 34 35 wings of spectral bands when the interferogram is not zero at its limits, by 36 multiplying the interferogram prior to Fourier transformation by a 37 weighting function that is zero at its limits (See: Fourier transform 38 spectroscopy). Its use has broadened in recent years to include weighting 39 functions that are not zero at their limits. 40 41 Note 2: Apodization is also used for manipulating FIDs (free induction decay) to 42 43 enhance specific components of the signal for example to improve signal- 44 to-noise or resolution and is achieved by application of specific shapes to 45 the FID, e.g. In nuclear magnetic resonance spectroscopy: exponential, 46 Gaussian or sine-bell; in infrared spectroscopy: Boxcar, Happ-Genzel, 47 Norton-Beer, cosine. 48 49 Source: [6]. 50 51 52 16. apodization function 53 window function 54 55 Mathematical function that effects apodization. 56 57 58 59 60

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1 2 3 17. array detector 4 5 6 Photoelectric detector in which a large number of pixels are distributed, usually in 7 regularly spaced lines, usually over a rectangular area. 8 9 Source: [6]. 10 11 18. asymmetric Fourier-transform spectroscopy 12 13 14 See: dispersive Fourier-transform spectroscopy. 15 16 19. attenuated total reflection, (ATR) 17 frustrated total internal reflection 18 For Peer Review Only 19 Internal reflection from an absorbing material at angles of incidence at or above the 20 21 critical angle. 22 23 See also: attenuated total reflection spectroscopy, multiple attenuated total reflection. 24 25 20. attenuation index 26 27 28 See: complex refractive index. 29 30 21. band 31 32 See: spectral band. 33 34 35 22. band-pass filter 36 bandpass filter 37 38 1. Optical filter that passes a spectral band of wavelengths within a certain range, 39 centred at a certain wavelength, and that rejects radiation of wavelength outside of the 40 range. 41 42 43 2. Electrical filter that passes a band of electrical signals with a certain frequency 44 range, centred at a certain frequency, that rejects signals at frequencies outside of the 45 range. 46 47 Source: [6]. See also: high-pass filter, low-pass filter. 48 49 50 23. bandwidth 51 52 See: spectral bandwidth. 53 54 24. beam splitter 55 56 57 Device to split a beam of electromagnetic radiation into two parts. 58 59 Note: In an ideal 2-beam Fourier-transform spectrometer the beam splitter would 60 transmit half of the radiation and reflect half of it to create the two beams.

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1 2 3 Source: [6]. 4 5 6 25. Beer-Lambert law 7 Beer-Lambert-Bouguer law 8 9 Absorbance of a beam of collimated monochromatic radiation in a homogeneous 10 isotropic medium is proportional to the absorption path-length, l, and to the 11 concentration, c, or (in the gas phase) to the pressure of the absorbing species. 12 13 14 Note 1: This law holds only under the limitations of the Lambert law [8] p361, and 15 for absorbing species exhibiting no concentration or pressure dependent 16 aggregation. 17 For Peer Review Only 18 0 Note 2: The law can be expressed as �(�) = lg �� = �(�)�� where the 19 ( �) 20 proportionality constant �(�) is the molar decadic absorption coefficient 0 21 and ��,�� are, respectively, the incident and transmitted spectral radiant 22 power. 23 24 25 Note 3: Spectral radiant power must be used because the Beer–Lambert law holds 26 only if the spectral bandwidth of the ultraviolet, visible, or infrared 27 radiation is narrow as compared to line widths in the spectrum. 28 29 Source: [8] p 307. 30 31 32 26. Cauchy function 33 2 2 34 Function y = a/(b +x ) where a and b are constants. If x is replaced by � ― �0 this 35 function yields a Lorentzian band centred at �0 . 36 37 38 Source: [6]. 39 40 27. charge coupled device, (CCD) 41 42 Device that stores information in the form of charge packets in an array of closely 43 spaced capacitors. 44 45 46 Note 1: The packets can be transferred from one capacitor to the next sequentially 47 by electronic manipulation, so that the information contained in the array 48 can be sequentially read electronically. 49 50 Note 2: In spectroscopy the charge packets are created by interaction with 51 radiation and the devices are extremely sensitive detectors for near IR and 52 53 visible radiation. 54 55 Source: [6]. 56 57 58 59 60

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1 2 3 28. circular birefringence 4 5 L 6 Difference between the refractive indices of an optically active medium for left, n , and R L R 7 right, n , circularly polarized radiation (n – n ) 8 9 Note 1: “Circular birefringence” is also used to describe the phenomenon of having 10 different refractive indices for left and right circularly polarized radiation. 11 12 L R 13 Note 2: Like the refractive indices (n , n ), circular birefringence changes with 14 wavenumber. 15 16 Source: [6]. 17 For Peer Review Only 18 29. complex refractive index, � 19 20 refractive index 21 22 Speed of light in a given medium divided by speed of light in vacuum. 23 24 Note 1: � = � + i�. The real part, n, is usually called the ‘refractive index’, and is 25 the entire refractive index when no radiation is absorbed. The imaginary 26 part, k, describes absorption (see absorption index). 27 28 29 Note 2: The older literature, and some physics literature today, uses � = �(1 + i�) 30 where κ is called the attenuation index. For simplicity, this usage is 31 discouraged. 32 33 Source: [3] p 37. 34 35 36 30. decadic absorbance, A10, A 37 38 Absorbance calculated with logarithm base 10. 39 40 Note: Confusion with Napierian absorbance must be avoided. 41 42 43 Source [3] p 36. 44 45 31. degeneracy, g 46 47 Number of states that have the same energy level. 48 49 50 Source: [6]. See also: accidental degeneracy. 51 52 32. dephasing 53 phase relaxation 54 55 Loss of coherence between the upper and lower states of a transition. 56 57 58 Note 1: The term ‘dephasing’ arises from the density matrix formalism that is used 59 in a phenomenological approach to simplify the description of the 60 relaxation dynamics of a molecule coupled to its surroundings.

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1 2 3 Note 2: Dephasing leads to either homogeneous broadening or inhomogeneous 4 broadening depending on the system. The continually changing 5 6 intermolecular interactions cause a shift of the frequency of the 7 intramolecular vibration. If these interactions change much more slowly 8 than the amplitude of this shift, heterogeneous broadening results and cause 9 a Gaussian band. If these interactions change much faster than the 10 amplitude of this shift, homogeneous broadening occurs and the observed 11 spectral band is a notionally narrowed Lorentzian band. In the general case 12 the broadening due to dephasing is neither homogeneous nor heterogeneous 13 14 and the line shape is neither Gaussian nor Lorentzian. 15 16 Source: [6]. 17 For Peer Review Only 18 33. derivative spectroscopy 19 20 21 Measurement method [VIM 2.5] of spectroscopy in which the absorbance, or other 22 spectral ordinate, is differentiated n times with respect to wavenumber or frequency to 23 give the nth derivative spectrum, i.e. the spectrum of the nth derivative of the original 24 spectrum. 25 26 Note: The technique is used to transform changes of slope in the original 27 28 spectrum into more prominent features in the derivative spectra and is 29 extensively used in the near-infrared to flatten spectral baselines to improve 30 subsequent chemometric study. 31 32 Source: [6]. 33 34 34. detector gate width 35 36 detector integration time 37 38 Time for signal integration after start of detection. 39 40 Note: Optimisation of gate width allows detection of species with different decay 41 rates. 42 43 44 Source: [6]. 45 46 35. difference spectroscopy 47 48 Measurement method [VIM 2.5] of spectroscopy in which spectral subtraction is used 49 to help the study and identification of individual species in a mixture. 50 51 52 Source: [6]. 53 54 36. diffuse reflectance, R 55 remittance 56 remission fraction 57 58 59 Diffuse reflected (remitted) radiant power (Prem) divided by incident radiant power 60 (P0). R = Prem/P0.

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1 2 3 Note 1: The sum of remittance, transmittance and absorptance equals one. 4 5 6 Note 2: Some authors distinguish between remittance and diffuse reflectance by 7 excluding specular reflection in the latter. 8 9 Source: [6]. 10 11 12 13 14 37. diffuse reflection 15 remission 16 17 Reflection inFor which electromagnetic Peer Review radiation incident Only on a scattering surface at a 18 certain angle is reflected (remitted) over all angles. 19 20 21 Note: Diffuse reflection is a complicated process and involves transmission, 22 reflection and scattering. 23 24 Source: [6]. See also: remittance. 25 26 38. diffuse transmission 27 28 29 Process in which radiation is transmitted by a scattering sample and leaves the sample 30 in directions other than that required by Snell’s law of refraction. The process is 31 complicated and involves transmission, reflection and scattering. 32 33 Source: [6]. See also: transmission. 34 35 36 39. dipole coupling 37 transition-dipole transition dipole coupling 38 39 Coupling of different motions through dipole-dipole forces. 40 41 Note: In vibrational spectroscopy of crystals, intermolecular vibrational coupling 42 43 through interaction of resonant transition dipoles throughout the whole 44 crystal. 45 46 Source: [6]. 47 48 40. dispersive Fourier-transform spectroscopy 49 50 asymmetric Fourier-transform spectroscopy 51 52 Fourier-transform spectroscopy using a Michelson or other two-beam interferometer 53 with the sample placed in one arm of the interferometer. 54 55 Note: This method provides information about the phase change as well as the 56 amplitude change caused by the sample. 57 58 59 Source: [6]. 60

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1 2 3 41. dispersive spectrometer 4 5 6 Spectrometer in which electromagnetic radiation is separated spatially into its 7 component wavenumbers by a dispersive element such as a prism or a diffraction 8 grating. 9 10 Source: [6]. 11 12 13 42. double-beam spectrometer 14 15 Spectrometer in which beams of electromagnetic radiation from the source reach the 16 detector via two paths, one through the sample and the other through a reference. 17 For Peer Review Only 18 Note 1: The radiant power in each beam is measured at each wavenumber. 19 20 21 Note 2: The output of a double beam spectrometer is termed a double beam 22 spectrum. The ordinate of a double-beam spectrum is the radiant power that 23 reaches the detector in the sample beam divided by that in the reference 24 beam. The spectrum has a flat baseline where the sample does not absorb. 25 26 Note 3: The reference is usually a material having the same composition as the 27 28 sample but lacking the analyte. 29 30 Source: [6]. 31 32 43. electric dipole moment, p, µ 33 dipole moment 34 35 36 Vector quantity of a dipole that in an electric field (E) has a potential energy 37 Ep = – p · E 38 39 Note 1: Today, the direction of the dipole moment is from the negative to the 40 positive charge. 41 42 43 Note 2: Electric dipole moment has also the magnitude of equal separated charges 44 of opposite sign times the distance between them. It is usually expanded as: 2 2 2 45 µ = µo + Σk (∂µ/∂Qk) Qk + Σk (∂ µ/∂Qk )Qk + Σi< j (∂µ/∂Qi) (∂µ/∂Qj)QiQj + 46 higher order terms, where the Qk, etc. are the normal coordinates and µo is 47 the equilibrium dipole moment of the molecule. 48 49 –30 50 Note 3: SI unit: C m. Common unit: Debye, D ≈ 3.335 64 × 10 C m. See Green 51 Book (3rd edition) p26 note 9 for alternative ways of expressing dipole 52 moment [3]. 53 54 Source: [3] p 26. 55 56 57 44. electromagnetic radiation, (EM) 58 radiation 59 60

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1 2 3 Flow of energy through space propagated as synchronized sinusoidal waves of the 4 electric field, E, and the magnetic field H. 5 6 7 Note 1: Electromagnetic radiation is characterized by frequency ν, wavelength λ, 8 and speed c, where νλ = c. 9 10 Note 2: The wavelength and velocity change when radiation enters a medium. In its 11 12 interaction with atoms and molecules, radiation behaves like particles, 13 called photons, with zero mass, energy hν, and momentum h/λ where h is 14 the Planck constant h = 6.626 070 15 × 10–34 J s. [9] 15 16 Source: [6]. 17 18 For Peer Review Only 19 45. electromagnetic transition 20 21 Transition accompanied by the emission or absorption of a photon. 22 23 Note 1: The frequency of the photon (v) is related to the energy difference of the 24 transition by hv = ∆E = |E – E |, where h is the Planck constant. 25 2 1 26 27 Note 2: In general, an electromagnetic transition obeys certain rules called 28 "electromagnetic selection rules". 29 30 Source: [10]. 31 32 46. electron emission spectrometry 33 34 35 Measurement principle [VIM 2.4] of spectrometry for the study of electrons emitted by 36 atoms. 37 38 See: 39 40 41 47. electronic transition 42 43 Transition in an atom, ion or molecule from an electronic energy level E1 to another 44 energy level E2. 45 46 Source: [10]. 47 48 49 48. emittance, ε 50 emissivity 51 52 Radiant excitance (M) emitted by the sample divided by radiant excitance emitted by a 53 black body (M ) at the same temperature. ε = M/M 54 bb bb 55 56 Note: The term “excitance” can be replaced by “power” or “flux” if the sample 57 and the black body have the same area and by intensity if, in addition, the 58 emission is measured as a collimated radiation beam. 59 60

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1 2 3 Source: [3] p 35. 4 5 6 49. energy level of a free atom, ion or molecule 7 energy level 8 energy state 9 10 Stationary quantum state of a free atom, ion or molecule having a particular internal 11 energy. 12 13 14 Note: SI unit: J. Common unit: electron volt, symbol eV, where 1 eV = 1.602 176 15 634 × 10–19 J. Energy levels are also expressed as kJ mol–1. 16 17 Source: [10]. 18 For Peer Review Only 19 50. excimer laser 20 21 22 Pulsed gas laser that typically emits radiation in the ultraviolet range. 23 24 Note: The lasing medium is made-up of gas mixture containing a halogen and a 25 noble gas such as Ar and F2 or Xe and Cl2. 26 27 28 Replaces [8] p336. 29 30 51. excitation energy 31 32 Minimum energy required to bring a system to a specified higher energy level. 33 34 35 Note: Usually excitation energy refers to the energy of transition from the ground 36 state to a higher energy level (excited state). 37 38 Source: [2] p 223. 39 40 52. excited state of a free atom, ion or molecule 41 excited state 42 43 44 Energy level of a free atom, ion or molecule of energy greater than that of the ground 45 state. 46 47 Source: [11] p 205. 48 49 50 53. experimental absorbance, A10 51 52 Decadic absorbance as measured with no corrections for other processes. 53 54 Note 1: The term emphasizes that radiation might be lost from the beam by 55 reflection, luminescence, scattering and possibly vignetting (e.g., spectral 56 shifts introduced from changing a radiation beam diameter or shape), and 57 58 not solely by absorption. 59 60

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1 2 3 Note 2: Internal absorbance is used to term absorbance corrected for other 4 processes. 5 6 7 Source: [6] 8 9 54. folding (in spectroscopy) 10 aliasing 11 12 13 Consequence of undersampling in spectroscopy. 14 15 Note In vibrational spectroscopy when a spectrum is sampled correctly only up 16 to a wavenumber �M, radiation of wavenumber � > �M appears to have a 17 wavenumber between 0 and �M , as follows: 18 For Peer Review Only 19 20 21 Range of wavenumber �app 22 � 23 [�M, 2�M] 2�M ― � 24 [2� , 3� ] � ― 2� 25 M M M 26 [3�M, 4�M] 4�M ― � 27 [4�M, 5�M] � ― 4�M 28 29 This process can be simulated by folding a spectrum that shows the correct 30 wavenumbers back onto itself at � and its multiples. 31 M 32 33 Source: [6]. See also: Nyquist criterion. 34 35 55. Fourier-transform spectroscopy 36 Fourier-transform spectrometry 37 38 39 Measurement method [VIM 2.5] whereby spectra are collected based on measurements 40 of the temporal coherence of a radiative source, using time-domain measurements of 41 electromagnetic radiation or other type of radiation. 42 43 Note 1: This procedure can be applied to a variety of spectroscopies including 44 optical-, Fourier-transform infrared spectroscopy (FT-IR), nuclear 45 46 magnetic resonance spectroscopy, and electron spin-resonance 47 spectroscopy. 48 49 Note 2: There are several methods for measuring the temporal coherence of the 50 radiation, including the CW (continuous wave) Michelson or Fourier- 51 transform spectrometer and the pulsed Fourier-transform spectrograph 52 (which is more sensitive and has a much shorter sampling time than 53 54 conventional spectroscopic techniques). 55 56 Source: [8] p 344. 57 58 59 60

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1 2 3 56. free induction decay, (FID) 4 5 6 Indication [VIM 4.1] from a pulsed spectroscopy experiment that takes the form of 7 damped sine waves arising from the excited system returning to equilibrium. 8 9 Note: In nuclear magnetic resonance spectroscopy the FID consists of sine waves 10 oscillating at the Larmor frequency (ω) and dampened by net dephasing 11 � ∗ 12 time relaxation (T2*), sin (��)exp( �2 ). 13 14 Source: [6]. 15 16 17 57. frequency, ν, f 18 For Peer Review Only 19 Number of cycles of periodic motion in unit time. 20 21 Note1: In spectroscopy the periodic motion is of the electric and magnetic vectors 22 of electromagnetic radiation. 23 24 25 Note 2: Frequency is related to the energy change of an electromagnetic transition, 26 ∆E, induced when electromagnetic radiation is absorbed through ∆E = hν, 27 where h is the Planck constant. 28 29 Note 3: SI unit: Hz, where 1 Hz = 1 s–1. 30 31 32 58. Fresnel reflection 33 34 Reflection of radiation from a surface that is smooth and large with respect to the 35 wavelength of the radiation. A reflected beam, of intensity governed by the Fresnel 36 equations, is produced at an angle of reflection equal to the angle of incidence. 37 38 39 Note: May be termed specular reflection for non-scattering samples. 40 41 Source: [6]. 42 43 59. frustrated multiple internal reflection, (FMIR) 44 45 46 See: multiple attenuated total reflection. 47 48 60. frustrated total internal reflection 49 50 See: attenuated total reflection. 51 52 53 61. full width at half maximum, (FWHM), W, Γ 54 full width at half height, (FWHH) 55 56 Interval between the two points across a section of a spectrum where the ordinate is 57 equal to half the maximum ordinate of the section. 58 59 Note 1: W is a measure of line or band width. 60

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1 2 3 Note 2: FWHM has units of wavelength, wavenumber, frequency or energy. 4 5 6 Note 3: For infrared absorption spectra, the FWHM must be measured from a 7 spectrum that is plotted linear in absorbance. 8 9 Note 4: In Raman spectra, the FWHM can be measured directly from the spectrum 10 of scattered light intensity unless the instrument response function varies 11 significantly across the band. 12 13 14 Note 5: Inclusion of “full” distinguishes FWHM from half-width at half maximum. 15 16 Source: [6], [8]. 17 For Peer Review Only 18 62. Gaussian band 19 20 2 2 21 Spectral band with the shape �G exp[ ―4ln 2(� ― �0) � ], where HG is the band 22 maximum (peak height), W is the full width at half maximum, �0 is the peak 23 wavenumber. 24 25 26 Source: [6]. 27 28 63. ground state of a free atom, ion or molecule 29 ground state 30 31 Energy level of minimum internal energy of a free atom, ion or molecule. 32 33 34 Note: It is conventional to assign the relative energy value of zero to this level. 35 36 Source: [6]. 37 38 64. Hadamard transform spectrometer 39 40 41 Multiplexing spectrometer that uses the optical components of a dispersive 42 spectrometer with a Hadamard encoding mask. 43 44 Source: [6]. 45 46 65. half width at half maximum, (HWHM) 47 48 half width at half height, (HWHH) 49 50 One half of the full width at half maximum. 51 52 Source: [6]. 53 54 55 66. high-pass filter 56 57 1. Optical filter that excludes radiation of wavenumber lower than a certain cut-on 58 value and passes radiation of wavenumber above this value. 59 60

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1 2 3 2. Electrical filter that blocks signal with a modulation frequency lower than a certain 4 cut-on value and passes signals of frequency above this value. 5 6 7 Source: [6]. See also: band-pass filter, low-pass filter. 8 9 67. Hilbert transforms of a spectrum 10 11 Functions that interrelate the real part, f ΄, and imaginary part, f ˝, of the refractive index, 12 � = � + i�or relative permittivity, � = �′ +��′′ through 13 14 ∞ 15 1 �′′(�) ′ ′ 16 � (�a) ― �∞ = � d� � ∫� ― �a 17 ―∞ 18 For Peer Review Only 19 ∞ ―1 �′(�a) ― �∞′ 20 �′′(�a) ― �∞′ = � d� 21 � ∫ � ― �a 22 ―∞ 23 24 where P means that the principal part of the integral is taken at the singularity. 25 Source: [6]. 26 27 68. imaginary refractive index 28 29 30 See: absorption index. 31 32 69. instrument line shape, (ILS) 33 34 Idealized form of a feature in a spectrometer corresponding to a transition. 35 36 37 Note 1: Ideal line shapes include Lorentzian, Gaussian and Voigt functions, whose 38 parameters are the line position, maximum height and half-width. 39 40 Note 2: For Fourier-transform spectra ILS varies with the apodization function 41 used. 42 43 44 Source: [6]. 45 46 70. integrated intensity 47 48 Area under a spectral band in an absorption spectrum where the absorption is linearly 49 proportional to the amount of absorber in unit area. 50 51 52 Note 1: The area under transmittance is not linearly proportional to amount of 53 absorber. 54 55 Note 2: The absorption quantity is usually a Beer-Lambert absorption coefficient, 56 but recently ��” (�) the wavenumber times the imaginary part of local 57 m 58 molar polarizability, has been used for neat liquids to correct for dielectric 59 effects. 60

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1 2 3 Source: [6]. See also: infrared intensity and associated entries within the Green Book 4 [3] p37. 5 6 7 71. integration range of a spectrum 8 integration range 9 10 Frequency or wavenumber range over which the integrated intensity of an absorption 11 band is measured by numerical integration of the area under the band. 12 13 14 Note 1: For Gaussian bands integration over one full width half maximum to each 15 side of the band centre yields 98% of the area under the band. 16 17 Note 2: LorentzianFor Peer bands integration Review over 3.1 or Only15.9 full width half maximum to 18 each side yields 90% and 98% of the band area. 19 20 21 Source: [6]. 22 23 72. intensified charge coupled device detector, (ICCD) 24 25 Charge coupled detector with a prior amplification system to improve sensitivity. 26 27 28 Note 1: The intensifier used is based on a microchannel plate (MCP), which 29 converts the incoming photons to electrons by means of a photocathode. 30 Generated electrons are multiplied in a second step by the MCP, and then 31 reconverted to photons using a phosphorous screen. Finally, derived 32 photons are detected with a CCD device. 33 34 Source: [6, 12]. 35 36 37 73. intensity of radiation, I, E 38 intensity 39 irradiance 40 deprecated: radiant flux 41 42 43 Radiant power (P) per unit area (A) that is received at a surface. I = dP/dA. 44 45 Note 1: Intensity and irradiance are formally the same quantity, but the term 46 intensity is usually used for collimated beams of radiation. (See [3] p35 47 Note 5). 48 49 –2 50 Note 2: SI unit: W m 51 52 Source: [3] p 35. See also: spectral intensity, radiant intensity. 53 54 74. intensity spectrum 55 56 See: single beam spectrum. 57 58 59 60

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1 2 3 75. interference (in analytical spectroscopy) 4 5 6 Effect that causes a change in the measured absorbance, or of the intensity for a given 7 concentration, due to the presence of one or more components accompanying the 8 analyte in the material submitted for, or the reagents used in the analysis. 9 10 Note: Interference in analytical spectroscopy should not be confused with 11 interference of beams in an interferometer. 12 13 14 Source: [10]. 15 16 76. interferometer 17 For Peer Review Only 18 Device in which beams of electromagnetic radiation are superimposed causing 19 interference in order to extract information. 20 21 22 See also: continuous scan interferometer, step-scan interferometer, Fourier-transform 23 spectroscopy. 24 25 77. internal absorbance, Ai 26 27 28 Absorbance in the absence of reflection, scattering or luminescence. 29 30 Note 1: Internal absorbance is a rarely used term in quantitative absolute intensity 31 studies to emphasize that the necessary corrections of the transmittance for 32 reflection and other cell effects have been made. Instrument manufacturers 33 usually use the raw, uncorrected transmittance when calculating the 34 absorbance. See experimental absorbance. 35 36 37 Note 2: Formally, Ai = –log10(1 – αi), Ai = –log10(Ti) for a sample that does not 38 scatter or luminesce, where αi is the internal absorptance and Ti is the 39 internal transmittance. 40 41 42 Source: [6]. 43 44 78. internal absorptance, αi 45 46 Absorptance fully corrected for surface effects and effects of the cell such as reflection, 47 48 scattering, luminescence and vignetting losses. 49 50 Note: If scattering and luminescence in the sample are negligible αi +Τi =1, where 51 Τi is internal transmittance. 52 53 54 Source: [3] p 36. 55 56 79. internal transmittance, Ti, τi 57 internal transmission 58 59 60

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1 2 3 Transmittance fully corrected for surface effects and effects of the cell such as 4 reflection, scattering, luminescence and vignetting losses. 5 6 7 Note: If scattering and luminescence in the sample are negligible αi +Τi =1 where 8 αi is internal absorptance. 9 10 Source: [6]. 11 12 13 80. irradiance 14 15 See: intensity of radiation. 16 17 81. isotropic 18 For Peer Review Only 19 20 Having properties that are independent of direction. 21 22 Source: [7] p 2198. See also: anisotropic. 23 24 82. Kramers-Kronig transforms of a spectrum 25 26 27 Functions based on the physical principle of causality that interconvert the real and 28 imaginary parts of complex optical quantities when they are known over a sufficiently 29 wide (strictly infinite) wavenumber range. They are frequently used to interconvert the 30 real part, f ′, and imaginary part, f ″, of the refractive index, � = � + i� , dielectric 31 constant (relative permittivity) , � = �′ +��′′ , or logarithm of the complex reflection 32 coefficient reiφ through 33 34 ∞ 35 2 ��′′(�) �′(�a) ― �∞′ = � d� 36 � ∫�2 ― �2 37 0 a 38

39 ―2�a ∞�′(�) ― �∞′ ′′ 40 � (�a) = � �∫ 2 2 d� 0 � ― �a P means that the principal part of the integral is taken at 41 where 42 43 the singularity. 44 45 Note: All functions used to model vibrational spectra obey the Kramers-Kronig 46 transforms as long as the real parts are even functions of wavenumber and 47 the imaginary parts are odd functions of wavenumber so that the Kramers- 48 Kronig transforms are equivalent to the Hilbert transforms. 49 50 51 Source: [6]. 52 53 83. laser 54 55 Source of ultraviolet, visible, or infrared radiation which produces light amplification 56 by stimulated emission of radiation from which the acronym is derived. 57 58 59 Note 1: The radiation emitted is coherent except for superradiance emission. 60

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1 2 3 Note 2: All lasers contain an energized substance that can increase the intensity of 4 radiation passing through it. 5 6 7 Source: [8] p 362. 8 9 84. light 10 11 Electromagnetic radiation visible to the human eye. 12 13 14 Note: In general, spectroscopic usage ‘light’ is synonymous with ‘radiation’ when 15 the specific wavelength is not relevant. 16 17 Source: [6]. 18 For Peer Review Only 19 85. linear decadic absorption coefficient, a, K 20 21 decadic absorption coefficient 22 23 Decadic absorbance (A10) divided by path-length (l). a = A10/l. 24 25 See also: linear Napierian absorption coefficient, molar decadic absorption coefficient, 26 molar Napierian absorption coefficient. 27 28 29 Source [3] p 36. 30 31 86. linear Napierian absorption coefficient, α 32 Napierian absorption coefficient 33 34 35 Napierian absorbance (Ae) divided by path-length (l). α = Ae/l. 36 37 Note: α is the reciprocal of the optical absorption depth 38 39 See also: linear decadic absorption coefficient, molar decadic absorption coefficient, 40 41 molar Napierian absorption coefficient. 42 43 Source [3] p 36. 44 45 87. liquid crystal tunable filter, (LCTF) 46 47 Optical device based on polarization interference caused by transmission through a 48 49 series of birefringent liquid crystal layers of different thicknesses that allow a narrow 50 wavelength region to be selected and tuned over a broad spectral range. 51 52 Source: [6]. 53 54 88. lock-in amplifier 55 56 57 Amplifier that amplifies only those signals that have, within a specified spectral 58 bandwidth, the same frequency as, and a specified phase relation with, the selected 59 reference signal. 60

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1 2 3 Source: [6]. 4 5 6 89. Lorentzian band 7 8 2 2 2 Band with the shape �L� [� + 4(� ― �0) ], where HL is the peak height, W is the 9 10 full width at half maximum, and �0 is the peak wavenumber. 11 12 Source: [6]. 13 14 90. low-pass filter 15 16 17 1. Optical filter that excludes radiation of wavenumber greater than a certain cut-on 18 value and passesFor radiation Peer of wavenumber Review below this Only value. 19 20 2. Electrical filter that blocks signal with a modulation frequency above a certain cut-on 21 value and passes signals of frequency below this value. 22 23 24 Source: [6]. See also: high-pass filter, band-pass filter. 25 26 91. magic angle 27 28 o 2 54.74 , the angle at which the Legendre polynomial P2(cos θ) = ½(3cos θ − 1) equals 29 zero. 30 31 32 Note 1: The name arises from solid state NMR, in which rapidly spinning a sample 33 about an axis at 54.74° to the magnetic field ‘magically’ converts into sharp 34 lines the very broad bands that are due to coupling of the magnetic dipoles 35 in the solid. 36 37 Note 2: This angle is important in the estimation of the molecular orientation in 38 39 polymer fibres by vibrational spectroscopy. In particular, if for a particular 40 vibrational band the dichroic ratio measured parallel and perpendicular to 41 the fibre axis is unity for many degrees of orientation of the fibre, then the 42 oscillating dipole must lie very close to 54.74o to the axis of the polymer 43 chain. 44 45 46 Source: [6]. 47 48 92. molar decadic absorption coefficient, ε 49 molar absorption coefficient 50 deprecated: extinction coefficient 51 deprecated: molar absorptivity 52 53 54 Decadic absorbance (A10) divided by path-length (l) and amount concentration (c). 55 ε = A10/cl. 56 57 Note: ‘Extinction coefficient’ or ‘molar absorptivity’ have been widely used for 58 the molar absorption coefficient, unfortunately often with values given in 59 60 ill-defined units. Use of this term has been discouraged since the 1960s,

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1 2 3 when international agreement with non-chemical societies reserved the 4 word ‘extinction’ for diffusion of radiation, i.e., the sum of the effects of 5 6 absorption, scattering and luminescence. 7 8 See also: linear decadic absorption coefficient, linear Napierian absorption coefficient, 9 molar Napierian absorption coefficient. 10 11 Source [3] p 36. 12 13 14 93. molar Napierian absorption coefficient, κ 15 16 Napierian absorbance (Ae) divided by path-length (l) and amount concentration (c). 17 κ = Ae/(cl). 18 For Peer Review Only 19 20 See also: linear decadic absorption coefficient, linear Napierian absorption coefficient, 21 molar decadic absorption coefficient. 22 23 Source [3] p 36. 24 25 94. multiple attenuated total reflection, (MATR) 26 27 multiple internal reflection, (MIR) 28 frustrated multiple internal reflection, (FMIR) 29 30 Process in which attenuated total reflection occurs sequentially several times with the 31 same sample. 32 33 Source: [6]. 34 35 36 95. Napierian absorbance, Ae, B 37 38 Absorbance calculated with logarithm base e (natural or Napierian logarithm). 39 40 Note1: Confusion with the decadic absorbance must be avoided. 41 42 43 Source: [3] p 36. 44 45 96. net absorption cross-section, σnet 46 absorption cross-section, σ 47 48 49 Molar Napierian absorption coefficient divided by the Avogadro constant. σnet = κ/NA. 50 51 Source: [3] p 37. 52 53 97. noise 54 55 56 Random fluctuations occurring in a signal that are inherent in the combination of 57 instrument and method. 58 59 60

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1 2 3 Note: Noise can be defined as peak-to-peak noise, which is the difference 4 between the largest and smallest values of these fluctuations in a given 5 6 region, or as root-mean-square noise, which is the standard deviation of the 7 noise in that region. For digital data with approximately 100 independent 8 data points, the peak-to-peak noise is about five times greater than the root- 9 mean-square 10 11 Source: [13] p1663. 12 13 14 Different kinds of noise are defined in Table 97.1 (Source [6]). 15 16 Table 97.1: Definitions of types of noise associated with spectroscopy. 17 Kind of noiseFor PeerDefinition Review Only Notes 18 1/f noise Noise for which the amplitude 19 20 increases as the modulation frequency 21 decreases. 22 23 24 amplifier-readout Noise that is observed, due to the 25 noise processes of reading an amplifier, in 26 the absence of analytical, background 27 28 and dark current signals. 29 excess dark current Noise in the dark current of a 30 noise photomultiplier tube or focal plane 31 array that is due to non-thermal 32 sources. 33 flicker noise Noise in excess of the quantum noise [1] 34 35 or shot noise that is proportional to the 36 multiplicative magnitude of the photon signal. 37 noise 38 Johnson noise Noise generated by the thermal 39 motion of electrons. 40 noise equivalent Incident radiation power that yields a 41 42 power, φN signal-to-noise ratio of 1 within a 43 bandwidth of 1 Hz at the wavelength 44 or wavenumber of interest 45 photomultiplier Noise caused by random fluctuations 46 (PMT) in the gain within a photomultiplier 47 multiplication tube due to the random nature of the 48 49 noise secondary emission of electrons at the 50 dynodes. 51 quantization noise Noise due to the finite resolution of 52 any readout device. 53 digitization noise 54 quantum noise Fundamental noise due to the random 55 56 emission of photons from a source. 57 Schottky noise Noise that is observed when a current 58 passes through or is generated at an 59 interface 60 shot noise Noise in the current or measured

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1 2 3 Kind of noise Definition Notes 4 5 voltage that is due to both quantum 6 noise and PMT multiplication noise. 7 white noise Noise that has approximately the same 8 amplitude at all frequencies 9 10 Note: [1] Flicker noise is usually caused by variations in the experimental 11 12 variables that control the radiance of the source (source flicker noise) or by 13 fluctuations in the sample (analyte flicker noise). 14 15 98. nominal spectral resolution 16 nominal resolution 17 resolution 18 For Peer Review Only 19 20 Spectral resolution setting on an instrument that a user sets to record a spectrum. 21 22 Note: The actual resolution achieved is related to this, to the width of the bands 23 studied and to the alignment of the instrument. 24 25 Source: [6]. 26 27 28 99. nonisotropic 29 30 See: anisotropic. 31 32 100. Nyquist criterion 33 34 Result of information theory that a sine wave can be completely reconstructed if its 35 36 ordinate is known at 2 or more points in a cycle. 37 38 Source: [6]. 39 40 101. Nyquist frequency, fNyquist 41 42 43 Highest frequency or wavenumber that can be characterized by sampling at a given rate 44 in order to be able to fully reconstruct the signal without artefacts. 45 46 Note: The Nyquist sampling theorem states that an FID or interferogram must be 47 sampled at a rate at least twice the highest frequency in the FID or 48 interferogram in order to reproduce the correct frequencies in an NMR or 49 50 Fourier-transform infrared spectrum, respectively, without folding (folding 51 in spectroscopy) artefacts. fNyquist = ½ ν. 52 53 Source: [14]. 54 55 102. path-length, l, s 56 57 path length 58 59 Length of the optical path through the sample. 60

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1 2 3 Note 1: In a transmission cell the path-length is usually taken as the distance 4 between the windows. 5 6 7 Note 2: SI unit: m. Commonly used SI unit: µm, mm 8 9 Source: [6]. See also: optical path difference. 10 11 103. phase relaxation 12 13 14 See: dephasing. 15 16 104. radiance, L 17 For Peer Review Only 18 Radiant power emitted or passing through a small transparent element of surface in a 19 20 given direction from the source about the solid angle Ω, divided by the solid angle and 21 by the orthogonally projected area of the element in a plane normal to the given beam 22 direction θ, dS⊥ = dS cos θ. 23 24 Note: SI unit: W sr–1 m–2. 25 26 27 Source: [8], [3] p 34. 28 29 105. radiant energy density, ρ, w 30 31 Radiant energy (Q) per unit volume (V). ρ = dQ/dV. 32 33 –3 34 Note: SI unit: J m 35 36 Source: [6], [3] p 34. 37 38 106. radiant excitance, M 39 emitted intensity 40 41 deprecated: emitted radiant flux 42 43 Radiant power emitted per unit area of the source. M = dP/dAsource 44 45 Note: SI unit: W m–2 46 47 48 Source: [3] p 34. 49 50 107. radiant intensity, Ie 51 52 Radiant power per solid angle in the direction of the point from which the source is 53 being viewed. I = dP/dΩ. 54 e 55 56 Note 1: Radiant intensity should not be confused with intensity of radiation 57 (irradiance). 58 59 Note 2: SI unit: W sr–1. 60

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1 2 3 Source: [3] p 34, 35. 4 5 6 108. radiant power, P, Φ 7 radiant flux 8 9 Radiant energy (Q) in unit time (t). P = dQ/dt. 10 11 Note 1: IUPAC in the third edition of the Green Book notes the previous use of 12 13 ‘flux’ for ‘flux density’ ([3] p81) but now recommends that ‘flux’ is simply 14 a rate of flow (of energy, mass, heat, radiation). 15 16 Note 2: SI unit: W 17 For Peer Review Only 18 Source: [3] p 34. 19 20 21 109. radiation 22 23 See: electromagnetic radiation. 24 25 110. radiofrequency, (RF) 26 27 4 12 28 Frequency or band of frequencies in the range 10 to 10 Hz. 29 30 111. received radiant flux density, I, E, φ0 31 incident flux density 32 irradiance 33 34 35 Radiant power incident on unit area. 36 37 Note 1: SI unit: W m–2 38 39 Note 2: In atomic absorption spectroscopy incident flux density at a given 40 wavelength is given the symbol φ (λ). 41 0 42 43 Source: [6]. See also: intensity of radiation. 44 45 112. reflectance, ρ, R 46 47 Spectral intensity reflected by the sample divided by spectral intensity incident on the 48 49 sample. 50 51 Note: For non-scattering and non-luminescent samples the sum of absorptance 52 (α), transmittance (τ) and reflectance (ρ) equals one. 53 54 Source: [6]. 55 56 57 58 59 60

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1 2 3 113. reflection 4 5 6 Process by which electromagnetic radiation is reflected by a sample. For non- 7 scattering samples the term means Fresnel reflection; for scattering samples the term 8 includes regular reflection and volume reflection or diffuse reflection. 9 10 Source: [6]. 11 12 13 114. refractive index 14 15 See: complex refractive index. 16 17 115. regular reflection 18 For Peer Review Only 19 See: specular reflection. 20 21 22 116. relative permittivity, εr 23 dielectric constant, � 24 25 3 × 3 tensor that gives to first order the electric displacement, D, in a material in terms 26 27 of the applied electric field, E, through D = εr εο E, where εο is the permittivity of 28 vacuum. 29 30 Note 1: For isotropic materials the tensor is diagonal with the 3 diagonal elements 31 equal, so a single quantity ε suffices. 32 33 34 Note 2: The equation D= εεοE is valid at all frequencies, and ε is a complex 35 quantity, � = �′ +��′′ , where ε˝ describes absorption. ε΄ is termed ‘real 36 dielectric constant’, and ε˝ is termed ‘imaginary dielectric constant’ 37 38 Note 3: Relative permittivity is the square of the refractive index, thus � = �2 or, for 39 2 40 a non-absorbing isotropic material, ε = n . 41 42 Source: [3] p 16, [6]. 43 44 117. remission 45 46 47 See: diffuse reflection. 48 49 118. remission fraction 50 51 See: diffuse reflection. 52 53 119. remittance 54 55 56 See: diffuse reflectance. 57 58 59 60

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1 2 3 120. resolving power, R 4 5 6 Wavelength (or wavenumber or frequency) divided by the spectral resolution at that 7 wavelength (or wavenumber or frequency); R = λ/δλ (=� δ� = � �� ). 8 9 Note: Resolving power characterizes the performance of a spectrometer, or the 10 degree to which a spectral line (or laser beam) is monochromatic. 11 12 13 Source: [3] p 36. 14 15 121. resolution 16 17 See: spectral resolution of an instrument. 18 For Peer Review Only 19 20 122. scattering coefficient, s, µs 21 22 Negative Napierian logarithm of the ratio of the intensity of radiation scattered (Is) by a 23 non-absorbing sample to the incident intensity (I0), divided by the path-length, l. 24 25 s = –ln(I /I ) /l 26 s 0 27 –1 28 Note: SI unit: m . 29 30 Source: [6]. 31 32 123. signal-to-noise ratio, (SNR, S/N, SNR ), R 33 dB S/N 34 35 Power of signal divided by power of noise. 36 37 Note 1: When signal and noise are measured cross the same impedance, SNR is 38 often calculated as the root-mean-squared amplitude of the signal divided 39 by the root-mean-squared amplitude of the noise. 40 41 42 Note 2: The value of signal-to-noise ratio may be expressed in decibel (SNRdB) as 43 ten times the logarithm to base 10 of signal-to-noise ratio. 44 45 Note 3: Initialisms should not be used to denote a quantity in expressions and 46 formulae. RS/N is recommended. 47 48 49 Source: [6]. 50 51 124. single beam spectrum 52 intensity spectrum 53 54 Output of a single beam spectrometer as a function of wavenumber or wavelength. 55 56 57 Note: A single-beam spectrum is often termed an ‘intensity spectrum’ (the 58 measured radiant power is the intensity times the area of the detector) and 59 does not have a flat baseline. 60

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1 2 3 Source: [6]. 4 5 6 125. single-beam spectrometer 7 8 Spectrometer that measures radiant power that reaches the detector at each wavelength 9 without reference to another spectrum in real time. 10 11 Note: Most Fourier-transform spectrometers are single-beam spectrometers. 12 13 14 Source: [6]. 15 16 126. slit width of a dispersive spectrometer 17 slit width 18 For Peer Review Only 19 Distance between the blades of the entrance or exit slits in a monochromator. 20 21 22 Note: Spectral slit width is the range of wavenumbers that the physical slit widths 23 allow to be passed by the monochromator and is often determined as the full 24 width at half maximum measured by the instrument for a line that is known 25 to be extremely sharp. 26 27 28 Source: [6]. 29 30 127. spectral band 31 band 32 33 Region of the absorption/transmission spectrum in which the absorbance/transmission 34 35 passes through a maximum/minimum. 36 37 Note: The use of the term “spectral band” implies a wider region of the spectrum 38 than “spectral line” (see: spectral line of an atom). 39 40 128. spectral bandwidth 41 bandwidth 42 43 44 Upper frequency minus lower frequency in a continuous band of frequencies. 45 46 Note: SI unit: hertz, Hz. 47 48 Source: [6]. 49 50 51 129. spectral intensity, Iṽ(ṽ), Eṽ(ṽ) 52 spectral irradiance 53 54 Intensity of radiation per unit wavenumber at wavenumber ṽ. Iṽ(ṽ) = dI/dṽ. 55 56 Note1: Spectral intensity and spectral irradiance are formally the same quantity, but 57 58 the term spectral intensity is usually used for collimated beams of radiation. 59 60 Note 2: SI unit: W m–1. Common unit W m–2/ cm–1.

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1 2 3 Source: [6], [3] p 34. 4 5 6 130. spectral radiance, Lṽ(ṽ), Lλ(λ) 7 spectral brightness 8 9 Radiance in unit wavenumber (wavelength) interval at wavenumber ṽ (wavelength λ). 10 11 –3 –1 –2 –1 –1 12 Note: SI unit: W m sr . Common unit: W m sr nm . 13 14 Source: [6], [8] p 2276. 15 16 131. spectral radiant energy density, ρ ṽ (ṽ), ρλ(λ) 17 18 For Peer Review Only 19 Radiant energy density in unit wavenumber (wavelength) interval at wavenumber ṽ 20 (wavelength λ). 21 22 Note: SI unit: J m–2 23 24 Source: [6]. 25 26 27 132. spectral range of a spectrometer 28 29 Wavelength range for which a spectrometer can be used. 30 31 Note: Spectral range depends essentially on the radiation source, the optical 32 33 components of the wavelength selector, and the detector. 34 35 Source: [10]. 36 37 133. spectral resolution of an instrument, �� , �� , �� 38 spectral resolution 39 resolution 40 41 42 Smallest difference between wavenumbers (or wavelengths or frequencies) at which 43 different spectral properties may be distinguished, measured as the full width at half 44 maximum. 45 46 Note 1: An equivalent definition is the minimum separation of two infinitely sharp 47 48 lines of equal intensity of radiation that allows the presence of two lines to 49 be seen in the measured spectrum. 50 51 Note 2: Resolution depends strongly on the instrument line shape “function” of the 52 spectrometer and on the natural line width. 53 54 Source: [3] p 36. See also: nominal spectral resolution. 55 56 57 134. spectral slit width 58 59 See: slit width of a dispersive spectrometer. 60

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1 2 3 135. spectral subtraction 4 5 6 Ordinate of one spectrum minus ordinate of another spectrum. 7 8 Note 1: Spectral subtraction may be used to improve the visibility of minor 9 components in the spectrum of a mixture. 10 11 Note 2: Successful use of the technique requires spectra, such as absorbance and 12 13 Raman spectra, in which the ordinate is linear in concentration, aprecisely 14 agreeing wavenumber scale and a very high signal-to-noise ratio. 15 16 Source: [6]. 17 For Peer Review Only 18 136. spectrometer 19 20 21 Measuring instrument [VIM 3.1] that separates electromagnetic radiation into its 22 component frequencies and transforms the radiant power at each frequency into an 23 electrical signal. 24 25 Source: [6]. 26 27 28 137. spectrum 29 30 Graph of a quantity derived from the radiant power at each wavelength (frequency or 31 wavenumber) as ordinate plotted against the wavelength (frequency or wavenumber) of 32 electromagnetic radiation as abscissa. 33 34 35 Note 1: In mid-infrared and Raman spectroscopy wavenumber is mostly used today 36 while it is more commonly replaced by wavelength in near infrared 37 spectroscopy. 38 39 Note 2: Quantities plotted include absorbance, absorption coefficient, 40 transmittance, reflectance, luminescence. 41 42 43 Source: [6]. 44 45 138. specular reflection 46 regular reflection 47 48 Reflection of electromagnetic radiation from a surface such that each incident ray is 49 50 reflected at the same angle to the surface normal as the incident ray, but on the 51 opposing side of the surface normal in the plane formed by incident and reflected rays. 52 53 Note 1: An image reflected by the surface in this way is reproduced in mirror-like 54 (specular) fashion. 55 56 Note 2: The term is used to distinguish the kind of reflection from diffuse reflection. 57 58 59 60

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1 2 3 139. stray light 4 5 6 Electromagnetic radiation that does not follow the usual path through a spectrometer 7 and consequently appears in a spectrum at a frequency or wavenumber different from 8 its initial value. 9 10 Note: The term is also used to refer to radiation that passes around the sample 11 instead of through it, and consequently is not modified by the sample and 12 13 seriously affects absolute and relative intensities. 14 15 Source: [6]. 16 17 140. superradiance emission 18 For Peer Review Only 19 See: laser. 20 21 22 141. transition 23 24 Change of energy level of a system. 25 26 Note: In spectroscopy a transition is caused by interaction of an atom, ion or 27 28 molecule with electromagnetic radiation. 29 30 Source: [6]. See also: electronic transition and electromagnetic transition 31 32 142. transition-dipole transition dipole coupling 33 34 35 See: dipole coupling. 36 37 143. transmission 38 39 Process in which electromagnetic radiation passes through a material, entering it on 40 one side and leaving it on another. 41 42 43 Note 1: For non-scattering, non-luminescent samples the transmitted beam obeys 44 Snell’s law of refraction, and the term internal transmission (see above) is 45 used when surface reflection effects are not included in transmission within 46 the sample. 47 48 Note 2: For scattering, non-luminescent materials transmission consists of two 49 50 processes, direct transmission, and diffuse transmission and is sometimes 51 called total transmission. 52 53 Source: [6]. 54 55 144. transmission factor 56 57 58 See: transmittance. 59 60

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1 2 3 145. transmission fraction 4 5 6 See: transmittance. 7 8 146. transmission spectrum 9 transmittance spectrum 10 11 General term for the spectrum of transmitted electromagnetic radiation. 12 13 14 Note: The ordinate quantity is usually the percentage of the incident radiation that 15 is transmitted, usually called the percent transmission, with range 0 to 100 16 %. If the ordinate quantity is the fraction transmitted, i.e., the 17 transmittanceFor Peer, the ordinate Review range is 0 to 1Only and the spectrum may be called a 18 transmittance spectrum. 19 20 21 Source: [6]. 22 23 147. transmittance, T, τ 24 transmission factor 25 transmission fraction 26 27 28 Transmitted radiant power at wavenumber � divided by incident radiant power. 29 30 Note 1: For non-scattering, non-luminescent samples the sum of absorptance (α), 31 transmittance (T), and reflectance (ρ) equals one. 32 33 34 Note 2: For scattering, non-luminescent samples the term ‘transmission fraction’ is 35 usually used instead of transmittance. 36 37 Source: [3] p 36. See also: percent transmission. 38 39 148. two-dimensional (2-D) correlation spectroscopy 40 41 42 Measurement principle [VIM 2.4] of spectroscopy in which spectra are recorded at 43 different magnitudes of an applied external perturbation of the sample and are 44 processed to yield a 2-D correlation spectrum. 45 46 Note 1: The external perturbation may be time dependent (chemical reactions, 47 physical relaxation processes), or static (temperature change, concentration 48 49 change). 50 51 Note 2: Correlation spectroscopy is used in infrared spectroscopy, nuclear 52 magnetic resonance spectroscopy (COSY, TOCSY), fluorescence 53 spectroscopy and others. 54 55 Source: [6]. See also: [15, 16]. 56 57 58 59 60

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1 2 3 149. two-dimensional (2-D) correlation spectrum 4 5 6 Three-dimensional surface in which two of the dimensions show frequency axes (ν1, ν2) 7 and the third axis shows a correlation function of the spectral intensities observed at ν1 8 and ν2. 9 10 Note 1: The shape of the surface shows whether the bands at the two wavenumbers 11 12 are or are not correlated, and hence allows deductions to be made about the 13 extent to which the different parts of the molecule are linked in their 14 response to the applied external perturbation. 15 16 Source: [6]. See dynamic spectrum. 17 18 For Peer Review Only 19 150. undersampling 20 21 Sampling less frequently than is required by the Nyquist criterion. 22 23 Note: Undersampling occurs when an analogue signal is digitized with less than 24 two data points per wavelength of the shortest wavelength (highest 25 wavenumber) radiation that reaches the detector. 26 27 28 Source: [6]. See: folding in molecular spectroscopy. 29 30 151. vacuum wavelength 31 32 See: wavelength in vacuum. 33 34 35 152. Voigt function 36 37 Convolution of Gaussian and Lorentzian (Cauchy) functions. 38 39 Source: [6]. 40 41 42 153. wavelength in medium, λ 43 wavelength 44 45 Distance travelled by a wave of electromagnetic radiation in one cycle in a non- 46 absorbing medium of real refractive index n. λ = λ0/n. 47 48 49 Note 1: In spectroscopy the unqualified term ‘wavelength’ frequently means the 50 vacuum wavelength, and symbol λ frequently means λ0. 51 52 Note 2: SI unit: m. Common unit: nm or µm 53 54 55 Source: [6]. 56 57 154. wavelength in vacuum, λ0 58 vacuum wavelength 59 60

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1 2 3 Distance travelled by a wave of electromagnetic radiation in one cycle in vacuum. 4 5 6 Note: SI unit: m. Common unit: nm or μm 7 8 Source: [6]. 9 10 155. wavenumber in medium, σ 11 wavenumber 12 13 14 Reciprocal of wavelength of electromagnetic radiation. σ =1/λ. 15 16 Note 1: In spectroscopy the unqualified term ‘wavenumber’ (sometimes referred to 17 asFor “reciprocal Peer centimetre” Review cm–1) often means Only vacuum wavenumber, and 18 symbol σ often means ṽ. 19 20 –1 –1 21 Note 2: SI unit: m . Common unit: cm . 22 23 Source: [6]. 24 25 156. wavenumber in vacuum, ṽ 26 27 vacuum wavenumber 28 29 Reciprocal of the vacuum wavelength of electromagnetic radiation. ṽ =1/ λ0. 30 31 Note 1: Wavenumber is related to the energy change, ΔE, induced when the 32 radiation is absorbed by ΔE = hcoṽ, where h is the Planck constant and co 33 the speed of the radiation. 34 35 36 Note 2: Wavenumber should only be used when no confusion with frequency is 37 possible. 38 39 Note 3: The symbol ν is often used instead of ṽ; this usage should be discouraged. 40 41 –1 –1 42 Note 4: SI unit: m . Common unit: cm . 43 44 Source: [6]. 45 46 157. window function 47 48 49 See: apodization function. 50 51 158. working range of a spectrometer 52 working range 53 54 Range of absorbance or intensity which a spectrometer can measure with prescribed 55 accuracy [VIM 2.13] and precision [VIM 2.15]. 56 57 58 Note: Working range varies in different parts of the spectral range. 59 60 Source: [10].

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1 2 3 159. zero filling 4 5 6 Addition of zeros to a free induction decay or interferogram to decrease the frequency 7 or wavenumber spacing between points in the Fourier-transformed spectrum. 8 9 Source: [6]. 10 11 160. zero path difference 12 13 14 In a Michelson interferometer or other two-beam interferometer, the position of the 15 moving mirror at which the optical paths are equal. 16 17 Source: [6]. 18 For Peer Review Only 19 NMR SPECTROSCOPY 20 21 22 Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a 23 magnetic field absorb and re-emit electromagnetic radiation. This energy is at a specific 24 resonance frequency which depends on the strength of the magnetic field and the 25 magnetic properties of the isotope of the atoms. Differentiation in NMR signals 26 between similar nuclei within a molecule is seen primarily due to differences in the 27 28 electron density at each nucleus. This variation in electron density is a consequence of 29 the geometric arrangement of atoms and the specific interaction with the electrons 30 surrounding them. 31 32 The propensity of a nucleus to undergo this phenomenon is dependent on its nuclear 33 spin, a net combination of the spins from the protons and neutrons within the nucleus. 34 All nuclei with a non-zero spin exhibit some NMR activity but those with a value of a 35 1 36 ½ are most amenable as they provide the simplest and best resolved spectra with H, 13 15 19 31 37 C, N, F and P being some of the most frequently studied nuclei. 38 39 NMR provides a rich source of information on the magnetic environment of each nuclei 40 through their chemical shifts, the connectivity of nuclei within a molecule through their 41 multiplicities and spin-spin couplings and the ratio of nuclei through their integrals. 42 43 NMR is used extensively for structural characterisation, quantitation of analytes, 44 biological imaging, inter-molecular interactions, reaction kinetics and assessment of 45 physical properties 46 47 The experimental manifestation of NMR, nuclear magnetic resonance spectroscopy, 48 usually involves three basic, sequential steps: 49 50 51 • The alignment (polarization) of the magnetic nuclear spins in an applied, static 52 magnetic induction B0. 53 • The perturbation of this alignment of the nuclear spins by employing 54 radiofrequency (RF) pulses. 55 • The detection of the RF as the nuclear spins return to equilibrium 56 57 58 59 60

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1 2 3 161. 13C-HMQC-NOESY 4 5 6 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 7 protein structure with 1 carbon and 2 hydrogen dimensions. 8 9 Note 1: In the initial HMQC step, magnetisation is transferred from 1H to 13C and 10 back again. This is then followed by a NOESY step in which the 11 magnetisation is transferred to any other hydrogen nucleus close by before 12 13 detection. 14 15 Note 2: The technique requires 13C labelling. 16 17 Note 3: The spectrum is used to obtain restraints for structure calculations. 18 For Peer Review Only 19 Source: [17]. See also: [18]. 20 21 22 162. 13C-NOESY-HSQC 23 24 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 25 protein structure with one carbon and two hydrogen dimensions. 26 27 28 Note 1: Magnetisation is exchanged between all hydrogens using the nuclear 13 29 Overhauser effect before being transferred to neighbouring C nuclei and 30 then back to 1H for detection. 31 32 Note 2: The spectrum is used to obtain restraints for structure calculations. 33 34 35 Source: [19]. See also: [6, 18]. 36 37 163. 15N-NOESY-HSQC 38 39 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 40 protein structure with 1 nitrogen and 2 hydrogen dimensions. 41 42 43 Note: Magnetisation is exchanged between all hydrogens using the nuclear 15 44 Overhauser effect before transferred to neighbouring N nuclei and then 45 back to 1H for detection. This spectrum can be used to obtain restraints for 46 structure calculations. 47 48 Source: [19]. See also: [18]. 49 50 51 164. 15N-TOCSY-HSQC 52 53 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 54 protein structure with 1 nitrogen and 2 hydrogen dimensions. 55 56 Note An isotropic mixing step transfers magnetisation between 1H spins. Then 57 15 1 58 the magnetisation is transferred to neighbouring N nuclei and back to H 59 for detection. This can help identify amino acid types. 60

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1 2 3 Source: [19]. See also: [18]. See also: total correlation spectroscopy. 4 5 6 165. 180° pulse 7 8 Pulsed radiofrequency signal in NMR that rotates the bulk magnetisation vector (M0) of 9 a nuclear spin to its opposing direction, effectively inverting the signal, (e.g. from the + 10 z to −z axis). 11 12 13 14 15 16 17 18 For Peer Review Only 19 20 21 Source: [20]. 22 23 166. 90° pulse 24 25 Pulsed radiofrequency signal that rotates the bulk magnetisation vector (M) of a nuclear 26 27 spin to its orthogonal plane. 28 29 Note: In a simple 1D NMR experiment this is from the z axis to the xy plane. 30 31 32 33 34 35 36 37 38 39 Source: [20]. 40 41 167. acquisition time, (AT), tacq 42 43 Duration of the digitization of a free induction decay. 44 45 Note: t = ½ N/f with number of data points N and NMR spectral width f 46 aq SW SW 47 48 Source: [14]. See also: dwell time. 49 50 168. adiabatic pulse 51 52 Radiofrequency pulse that inverts spins by using a frequency sweep during the pulse. 53 54 55 Note 1: Adiabatic pulse allows very high spectral bandwidth and accurate flip 56 angles to be achieved with high tolerance to spatial variations in RF field 57 intensity and is thus of value in excitation of nuclei with frequency ranges. 58 59 60

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1 2 3 Note 2: the sweep must be slow enough to satisfy the adiabatic condition d� d� 4 5 ≪ ��eff where Beff is the effective radiofrequency magnetic flux density 6 and θ is the angle between Beff and abscissa. 7 8 Source: [21]. 9 10 169. Bloch equations 11 12 13 Set of coupled differential equations which can be used to describe the behaviour of a 14 magnetization vector under any conditions. 15 16 Note: When properly integrated, Bloch equations yield X', Y', and Z' components 17 of magnetization within the rotating frame of reference as a function of time 18 For Peer Review Only 19 20 Source: [22]. 21 22 170. Bloch Siegert shift 23 24 Frequency difference seen for a nuclear magnetic resonance signal when a 25 radiofrequency field is applied during the acquisition time. 26 27 28 Note: The shift arises from the effective magnetic field generated by the applied 29 RF field. The resonances are always moved away from the frequency of 30 the irradiating field and are inversely proportional to the difference in 31 frequency between the irradiation and the resonance. 32 33 34 Source: [21]. 35 36 171. Boltzmann distribution of nuclear spins 37 38 Distribution of nuclear spins among their possible energy levels at thermal equilibrium. 39 40 Note: For a positive gyromagnetic ratio, produces population excess 41 42 (polarization) in the direction of B0. The population difference can be 43 expressed as 44 45 �� ― �� 46 �� 47 = � �� 48 ― ∑� �� 49 � = 1� 50 51 52 where Ni is the number of spins in excited state i, N is the total number of 53 spins and εi and εj are the energies of states i and j respectively. 54 55 172. CBCA(CO)NH / HN(CO)CACB 56 57 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 58 protein structure with nitrogen, carbon and hydrogen dimensions. 59 60

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1 2 3 Note: Magnetisation is transferred from 1Hα and 1Hβ to 13Cα and 13Cβ, 4 respectively, and then from 13Cβ to 13Cα. From here it is transferred first to 5 13 15 1 6 CO, then to NH and then to HN for detection. Along with CBCANNH 7 and HSQC this forms the standard set of experiments needed for backbone 8 assignment. 9 10 Source: [23]. See also: [18]. 11 12 13 173. CBCANH / HNCACB 14 15 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 16 protein structure with nitrogen, carbon and hydrogen dimensions. 17 For Peer Review Only 18 Note 1: Magnetisation is transferred from 1Hα and 1Hβ to 13Cα and 13Cβ, 19 respectively, and then from 13Cβ to 13Cα. From here it is transferred first to 20 15 1 21 NH and then to HN for detection. For each NH group there are two Cα 22 and Cβ peaks visible. Along with the CBCA(CO)NNH and HSQC this 23 forms the standard set of experiments needed for backbone assignment. 24 25 Source: [17]. See also: [18]. 26 27 28 174. CC(CO)NH 29 30 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 31 protein structure with nitrogen, carbon and hydrogen dimensions. 32 33 Note 1: Magnetisation is transferred from the side-chain hydrogen nuclei to their 34 attached 13C nuclei. Then isotropic 13C mixing is used to transfer 35 36 magnetisation between the carbon nuclei. From here, magnetisation is 37 transferred to the carbonyl carbon, on to the amide nitrogen and finally the 38 amide hydrogen for detection. The chemical shift is evolved simultaneously 39 on all side-chain carbon nuclei, as well as on the amide nitrogen and 40 hydrogen nuclei, resulting in a three-dimensional spectrum. 41 42 43 Note 2: This method is a useful spectrum for obtaining carbon side-chain 44 assignment. 45 46 Source: [24]. See also: [18]. 47 48 175. chemical shift anisotropy in NMR, (CSA) 49 50 Chemical shift difference between isotropic and anisotropic states in nuclear 51 52 magnetic resonance spectroscopy. 53 54 Note 1: Nuclei which are part of a specific functional group resonate at different 55 frequencies depending on shielding by the local electronic environment and 56 thus can give information on their relative orientation. 57 58 59 Note 2: Chemical shift anisotropy also contributes to nuclear spin relaxation. 60

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1 2 3 Source: [25]. 4 5 6 176. chemical shift in NMR, δ 7 8 The fractional variation of the resonance frequency of a nucleus in nuclear 9 magnetic resonance spectroscopy relative to the resonance frequency of the nucleus in 10 a given reference in consequence of its magnetic environment. 11 12 13 Note 1: The chemical shift for nucleus X in sample s, �X,s is 14 (�X,s ― �X,r) 15 �X,s = where �X,s is the resonance frequency of X in the sample �X,r 16 17 and �X,r is the resonance frequency in the reference. 18 For Peer Review Only 19 Note 2: Chemical shift is usually reported in ‘parts per million’ or ppm, where the 20 21 difference of frequencies in the numerator have unit Hz, and the frequency 22 of the reference in the denominator has unit MHz. 23 24 Note 3: The alternative use of Hz/MHz is recommended as best practice in the 25 Green Book to remove ambiguity regarding the symbol ppm. 26 27 Source: [4] p 1807. 28 29 30 177. combined rotation and multiple pulse spectroscopy, (CRAMPS) 31 32 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy for 33 obtaining high-resolution solid-state nuclear magnetic resonance spectra on nuclei with 34 high gyromagnetic ratio such as 1H and 19F. 35 36 37 Note: CRAMPS is based on coherent-averaging theory, which attempts to 38 describe the time evolution of a system in terms of an average Hamiltonian 39 derived from the density matrix formalism of quantum mechanics. 40 41 Source: [26]. 42 43 44 178. constant time evolution 45 46 Segment of a pulse sequence in nuclear magnetic resonance spectroscopy that allows 47 evolution of chemical shift during a fixed time period rather than through the traditional 48 symmetrical incremented delays. 49 50 51 Source: [21]. 52 53 179. correlation spectroscopy in NMR, (COSY) 54 55 Homonuclear two-dimensional nuclear magnetic resonance spectroscopy correlation 56 experiment showing cross peaks representing spin-spin coupling between pairs of 57 58 nuclei. 59 60

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1 2 3 Note 1: COSY is the simplest and original 2D experiment, but still one of the most 4 common along with its many variations including those with multiple 5 6 quantum filters, solvent suppression and optimisation for long range 7 couplings. 8 9 Note 2: often used to show the spin-spin coupling between hydrogen nuclei 2 or 3 10 bonds apart (H,H-COSY). 11 12 13 Source: [27]. See also: correlation spectroscopy. 14 15 180. correlation spectroscopy through long-range coupling, (COLOC) 16 17 HeteronuclearFor (typically Peer 13C) detected Review long range 2D Only correlation experiment in nuclear 18 magnetic resonance spectroscopy that has mostly been superseded by heteronuclear 19 multiple bond correlation (HMBC) experiments and its variants. 20 21 22 Note 1: COLOC is often used to show spin-spin coupling between hydrogen and 23 carbon nuclei 2 and 3 bonds apart. 24 25 Source: [27]. See also: [18]. 26 27 181. correlation time, τ,τc 28 Parameter related to the mean time during which a molecule maintains its spatial 29 30 geometry. 31 32 Note: For an internuclear vector, correlation time is approximately equal to the 33 average time for it to rotate through an angle of one radian. 34 35 Source: [22]. 36 37 38 182. coupling constant 39 40 See: spin-spin coupling constant. 41 42 183. cross polarisation with magic angle spinning NMR, (CP/MAS) 43 44 45 Combined use of cross polarization with magic-angle spinning for solid-state nuclear 46 magnetic resonance spectroscopy. 47 48 Source: [27]. 49 50 184. cross polarization 51 52 53 Technique in solid-state nuclear magnetic resonance spectroscopy that enables 54 polarization from abundant spins such as 1H or 19F to be transferred to dilute spins such 55 as 13C or 15N to enhance signal-to-noise ratio. 56 57 Note: Cross polarization requires that nuclei are dipolar coupled to one another. 58 59 60

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1 2 3 185. cross-relaxation appropriate for minimolecules emulated by locked spins, 4 (CAMELPSIN) 5 6 7 See: rotating-frame NOE spectroscopy. 8 9 186. decoupling 10 11 See: heteronuclear decoupling, homonuclear decoupling. 12 13 14 187. decoupling in the presence of scalar interactions, (DIPSI) 15 16 Pulse sequence in nuclear magnetic resonance spectroscopy often used for isotropic 17 mixing in totalFor correlation Peer spectroscopy Review (TOCSY) experiments Only due to its efficiency 18 over large spectral bandwidths. 19 20 21 Source: [21]. 22 23 188. diffusion ordered spectroscopy, (DOSY) 24 25 Pseudo-two-dimensional nuclear magnetic resonance spectroscopy experiment that 26 resolves NMR signals of a one-dimensional nuclear magnetic resonance spectrum in a 27 28 second dimension through the diffusion times of their corresponding molecules. 29 30 Note 1: DOSY is used to differentiate signals from different molecules based on 31 their effective sizes. 32 33 Note 2: DOSY relies on spatially encoding the analyte by use of pulsed-field 34 35 gradients. 36 37 Source: [21]. 38 39 189. dipolar coupling in nuclear magnetic resonance spectroscopy 40 magnetic dipole–dipole interaction in NMR 41 42 43 Direct though-space interactions of nuclear magnetic moment vectors proportional to 44 the inverse cube of internuclear distance. 45 46 Note: In isotropic solution, dipolar couplings average to zero as a result of 47 diffusion but are present in solid-state nuclear magnetic resonance 48 spectroscopy and their effect on nuclear spin relaxation are measurable 49 50 through nuclear Overhauser effects (NOEs). 51 52 Source: [22]. 53 54 190. distortionless enhancement by polarisation transfer, (DEPT) 55 56 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy used for 57 58 determining the presence of primary, secondary and tertiary heteronuclei. 59 60 Note 1: DEPT is a 1D technique which is use typically for 13C.

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1 2 3 13 Note 2: The DEPT experiment for C differentiates between CH, CH2 and CH3 4 groups by variation of the selection angle parameter (the flip angle of the 5 6 final 1H pulse): 135° angle gives all CH and CH3 in a phase opposite to 7 CH2; 90° angle gives only CH groups, the others being suppressed; 45° 8 angle gives all carbons with attached protons with the same phase. 9 10 Source: [27]. 11 12 191. double pulsed-field gradient spin-echo excitation, (DPFGSE) 13 14 15 Pulse sequence in nuclear magnetic resonance spectroscopy in which pulsed-field 16 gradients are applied to a doubled spin echo sequence to cleanly and precisely excite 17 particular resonances. 18 For Peer Review Only 19 Source: [28]. 20 21 22 192. double resonance 23 24 Nuclear magnetic resonance spectroscopy experiment where excitation is applied 25 independently to two distinct frequency ranges. 26 27 Note: Double resonance is most commonly applied for spin decoupling. 28 29 30 Source: [20]. 31 32 193. double-labelled protein 33 34 Shorthand for a protein which has been uniformly 15N- and 13C-labelled. 35 36 37 194. double-quantum filtered correlation spectroscopy, (DQF-COSY) 38 39 Variant of the COSY experiment with a double quantum filter to remove, or at least 40 reduce, impact of large singlet peaks on dynamic range and artefacts. 41 42 Source: [27]. 43 44 45 195. dwell time, (DW), τd 46 Time interval between sampled data points. 47 48 Note: τ = 1/� , where � is the NMR spectral width 49 d SW SW 50 51 Source: [21]. See also: acquisition time. 52 53 196. echo time, (TE), TE 54 55 In nuclear magnetic resonance spectroscopy, time interval between the middle of the 56 57 first radiofrequency pulse and the peak of the spin echo. 58 59 Source: [21]. 60

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1 2 3 197. electronic reference to access in vivo concentrations, (ERETIC) 4 5 6 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy that 7 generates an electronic signal in a nuclear magnetic resonance spectrometer which is 8 detected simultaneously to the sample free induction decay during the acquisition. 9 10 Note: This approach is used to simplify the quantification of signals in the 11 resulting NMR spectra by avoiding the need for the use of internal or 12 13 external reference materials. 14 15 Source: [29]. 16 17 198. Ernst angle, θ E 18 For Peer Review Only 19 20 In a single-pulse nuclear magnetic resonance spectroscopy experiment when signal 21 averaging, flip angle giving the best signal-to-noise ratio for a given combination of 22 spin-lattice relaxation time and repetition rate. 23 24 Note: Named after Richard Ernst. It is employed to allow the maximum signal to 25 noise to be generated in a fixed amount of time. 26 (�d + �acq) 27 ― �1 cos (�E) = � where td is the interpulse delay, tacq is the 28 acquisition time, and T is longitudinal relaxation time. 29 1 30 31 32 33 Source: [21]. 34 35 199. exchange spectroscopy, (EXSY) 36 37 38 Nuclear magnetic resonance spectroscopy experiment, which is the same as a NOESY 39 but for the purposes of observing nuclei exchanging chemical environments during the 40 course of the experiment through conformational or chemical exchange. 41 42 Source: [27]. 43 44 45 200. excitation sculpting 46 47 Robust method of generating selective excitation through combination of shaped pulses 48 and pulsed-field gradients in nuclear magnetic resonance spectroscopy. 49 50 Source: [21]. 51 52 53 201. fast field cycling NMR relaxometry, (FFC-NMR) 54 55 Relaxometry to measure the nuclear spin-lattice relaxation rate constant as a function of 56 the applied magnetic field strength in nuclear magnetic resonance spectroscopy. 57 58 59 60

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1 2 3 Note: FFC-NMR is used to study molecular dynamics of molecules across a range 4 of applications including molecular motion in solids and ligand - metal 5 6 binding. 7 8 Source: [30]. 9 10 202. flip angle, α 11 tip angle 12 13 14 Rotation nuclear magnetic resonance spectroscopy that the net magnetization 15 experiences during application of a radiofrequency pulse. 16 17 Note: For a strong and rectangular RF-pulse of constant amplitude (B1) and 18 For Peer Review Only duration (tp), the resultant flip angle is approximately proportional to the 19 frequency (f ) of the B field: � = � × � × � , where γ is the gyromagnetic 20 1 1 1 p 21 ratio. 22 23 203. gated decoupling 24 25 Application of spin decoupling only during selected time periods in a pulse experiment 26 27 in nuclear magnetic resonance spectroscopy. 28 29 Note 1: Gated decoupling is used to eliminate either 1H – 13C spin-spin coupling or 30 the nuclear Overhauser effect from a 1D 13C spectrum. 31 32 Note 2: If the decoupler is turned off during acquisition this is usually referred to as 33 ‘gated decoupling’ while decoupling turned on during acquisition is usually 34 35 referred to as ‘inverse gated decoupling’. 36 37 Source: [20]. 38 39 204. globally optimized alternating-phase rectangular pulses, (GARP) 40 41 42 Spin decoupling pulse sequence in nuclear magnetic resonance spectroscopy used to 43 provide decoupling over a large frequency range. 44 45 Note: GARP is typically used to remove 13C sidebands in 1H nuclear magnetic 46 resonance spectra. 47 48 Source: [27]. 49 50 51 205. gradient pulse 52 53 See: pulsed-field gradient. 54 55 206. gradient-selected experiment 56 57 58 Nuclear magnetic resonance spectroscopy experiment where pulsed-field gradients are 59 employed to filter out unwanted resonances from a spectrum rather than the classic 60 phase-cycling approach.

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1 2 3 Source: [27]. 4 5 6 207. gyromagnetic ratio, γ 7 magnetogyric ratio 8 9 Magnetic moment µ of a nuclide divided by its spin angular momentum J. 10 11 ℎ �(� + 1) 12 � = �� = �( 2�) , where I is the spin quantum number of the nuclide and h is 13 the Planck constant. 14 15 Note 1: � can be either positive (e.g. 1H, 13C) or negative (15N, 29Si). For particular 16 values of the magnetic induction B0 and the magnetic quantum number m , � 17 ℎ 18 determinesFor Peer the energy Reviewlevel of the nucleus. Only � = ―��( 2�)�0 19 20 Note 2: SI unit: rad s–1 T–1 ≡ C kg–1. 21 22 Source: [31]. 23 24 25 208. H(CCO)NH 26 27 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 28 protein structure with 1 nitrogen, and 2 hydrogen dimensions. 29 30 Note 1: Magnetisation is transferred from the side-chain hydrogen nuclei to their 31 13 13 32 attached C nuclei. Then isotropic C mixing is used to transfer 33 magnetisation between the carbon nuclei. From here, magnetisation is 34 transferred to the carbonyl carbon, on to the amide nitrogen and finally the 35 amide hydrogen for detection. 36 37 Note 2: Requires 15N and 13C labelling 38 39 40 Note 3: Useful spectrum for obtaining hydrogen side-chain assignments. 41 42 Source: [32]. See also: [18]. 43 44 209. HBHA(CO)NH 45 46 47 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 48 protein structure with one nitrogen and two hydrogen dimensions. 49 50 Note 1: Magnetisation is transferred from 1Hα and 1Hβ to 13Cα and 13Cβ, 51 respectively, and then from 13Cβ to 13Cα. From here it is transferred first to 52 13CO, then to 15NH and then to 1HN for detection. 53 54 55 Note 2: Useful spectrum for obtaining Hα and Hβ assignments. 56 57 Source: [33]. See also: [18]. 58 59 60

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1 2 3 210. HCCH-COSY 4 5 6 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 7 protein structure with 1 carbon and 2 hydrogen dimensions. 8 9 Note 1: Magnetisation is transferred from the side-chain hydrogen nuclei to their 10 attached 13C nuclei. Magnetisation is then exchanged between neighbouring 11 13C nuclei via the J-coupling and finally transferred back to the side-chain 12 13 hydrogen atoms for detection. 14 15 Note 2: The nuclear magnetic resonance spectrum can be useful in aiding side- 16 chain assignment. 17 18 For Peer Review Only Source: [34]. See also: [18]. 19 20 21 211. HCCH-TOCSY 22 23 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 24 protein structure with 1 carbon and 2 hydrogen dimensions. 25 26 Note 1: Magnetisation is transferred from the side-chain hydrogen nuclei to their 27 13 13 28 attached C nuclei. This is followed by isotropic C mixing and finally the 29 transfer back to the side-chain hydrogen atoms for detection. 30 31 Note 2: The nuclear magnetic resonance spectrum is used for side-chain 32 assignment. 33 34 Source: [35]. See also[18]. See also: total correlation spectroscopy. 35 36 37 212. Hahn echo 38 39 See: spin echo. 40 41 213. heteronuclear decoupling 42 43 decoupling 44 45 Spin decoupling in nuclear magnetic resonance spectroscopy between two different 46 nuclei (e.g. 13C and 1H) by appropriate excitation of the decoupled nucleus. 47 48 Note 1: Heteronuclear decoupling is normally performed to simplify spectra or to 49 50 enhance signal-to-noise ratio by combining individual components of the 51 NMR signal. 52 53 Note 2: Notation 13C{1H} denotes observation of 13C nucleus with simultaneous 54 decoupling of 1H nuclei. 55 56 Source: [20]. See also: homonuclear decoupling. 57 58 59 60

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1 2 3 214. heteronuclear multiple bond correlation NMR, (HMBC) 4 5 6 Two-dimensional nuclear magnetic resonance spectroscopy that gives correlations 7 between carbons and protons that are separated by two, three, and, sometimes in 8 conjugated systems, four bonds. 9 10 Note 1: Direct one-bond correlations are suppressed. 11 12 13 Note 2: HMBC gives connectivity information much like a proton-proton COSY. 14 15 Note 3: The intensity of cross peaks depends on the spin-spin coupling constant, 16 which for three-bond couplings follows the Karplus relationship. For 17 dihedralFor anglesPeer near 90 Review°, the coupling is nearOnly zero. Thus, the absence of a 18 cross peak does not confirm that carbon-proton pairs are many bonds apart. 19 20 21 Note 4: Because of the wide range (0 to14 Hz) of possible carbon-proton couplings, 22 two experiments are often performed. One optimized for 5 Hz couplings 23 and the second optimized for 10 Hz. This gives the optimum signal-to-noise 24 ratio. Alternatively, a comprise value of 7-8 Hz can be used. There are also 25 "accordion" versions that attempt to sample the full range of couplings. 26 27 28 Source: [36]. 29 30 215. heteronuclear multiple-bond correlation over two bonds, (H2BC) 31 32 Variant of the heteronuclear single quantum correlation (HSQC) and heteronuclear 33 multiple bond correlation (HMBC) experiment in nuclear magnetic resonance 34 1 35 spectroscopy that almost exclusively correlates H nuclei with heteronuclei separated 36 by 2 covalent bonds. 37 38 Source: [19]. See also: [18]. 39 40 216. heteronuclear multiple-quantum correlation NMR, (HMQC) 41 42 1 43 Simplest implementation of an inverse detected H heteronuclear correlation nuclear 44 magnetic resonance spectroscopy experiment. 45 46 Source: [27]. 47 48 217. heteronuclear multiple-quantum correlation with additional TOCSY 49 50 transfer, (HMQC-TOCSY) 51 52 Variant of heteronuclear multiple bond correlation (HMBC) spectroscopy that shows 53 correlations from a heteronucleus (e.g.13C) to not only its directly bound 1H but also to 54 all other 1H nuclei within the spin system. 55 56 57 Source: [27]. See also: total correlation spectroscopy. 58 59 60

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1 2 3 218. heteronuclear Overhauser effect spectroscopy, (HOESY) 4 5 6 Heteronuclear variant of nuclear Overhauser effect spectroscopy (NOSEY) showing 1 13 7 through space interaction between H and a heteronucleus, typically C. 8 9 Source: [27]. 10 11 219. heteronuclear shift correlation NMR, (HETCOR) 12 13 14 Directly-observed one-bond heteronuclear correlation experiment in nuclear magnetic 15 resonance spectroscopy . 16 17 Note: HETCORFor Peer has largely Reviewbeen replaced by the Only indirectly observed 18 heteronuclear single quantum correlation experiment due to its greater 19 sensitivity. It does however have the advantage of greater resolution in the 20 21 heteronuclear dimension. 22 23 Source: [27]. 24 25 220. heteronuclear single quantum correlation, (HSQC) 26 heteronuclear single quantum coherence 27 28 1 29 H (inverse) detected two-dimensional nuclear magnetic resonance spectroscopy 30 heteronuclear experiment that correlates 1H nuclei with their directly coupled nucleus 31 through a single bond. 32 33 Source: [27]. 34 35 36 221. heteronuclear single quantum correlation with additional TOCSY 37 transfer, (HSQC-TOCSY) 38 39 Variant of the heteronuclear single quantum correlation (HSQC) experiment that 40 shows correlations from a heteronucleus (e.g.13C) to not only its directly bound 1H but 41 also to all other 1H nuclei within the spin system. 42 43 44 Source: [27]. See also: total correlation spectroscopy. 45 46 222. heteronuclear single quantum multiple-bond correlation, (HSQMBC) 47 48 Variant of the heteronuclear single quantum correlation (HSQC) experiment that 49 50 provides pure absorption, antiphase line shapes for precise, direct measurement of n 51 J(C,H) spin-spin coupling constants. 52 53 Source: [19]. See also: [18]. 54 55 223. HN(CA)CO 56 57 58 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 59 protein structure with nitrogen, carbon and hydrogen dimensions. 60

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1 2 3 Note 1: the magnetisation is transferred from 1H to 15N and then via the N-Cα J- 4 coupling to the 13Cα. From there it is transferred to the 13CO via the 13Cα- 5 13 6 CO J-coupling. For detection the magnetisation is transferred back the 13 13 15 1 7 same way: from CO to Cα, N and finally H. 8 9 Note 2: each NH group will show correlations to both their own and adjacent 10 carbonyls group. 11 12 13 Source: [37]. See also: [18]. 14 15 224. HN(CO)CA 16 17 Three-dimensionalFor nuclear Peer magnetic Review resonance spectroscopy Only for the assignment of 18 protein structure with nitrogen, carbon and hydrogen dimensions. 19 20 1 15 13 21 Note: The magnetisation is passed from H to N and then to CO. From here it 13 22 is transferred to Cα and the chemical shift is evolved. The magnetisation 23 is then transferred back via 13CO to 15N and 1H for detection. This is similar 24 to the HNCA, but is selective for the Cα of the preceding residue. 25 26 Source: [38]. See also: [18]. 27 28 29 225. HNCA 30 31 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 32 protein structure with nitrogen, carbon and hydrogen dimensions. 33 34 Note: The magnetisation is passed from 1H to 15N and then via the N-Cα J- 35 13 15 1 36 coupling to the Cα and then back again to N and H hydrogen for 37 detection. Each NH group will show correlations to both their own and the 38 previous residue’s 1Cα. 39 40 Source: [39]. See also: [18]. 41 42 43 226. HNCO 44 45 Three-dimensional nuclear magnetic resonance spectroscopy for the assignment of 46 protein structure with nitrogen, carbon and hydrogen dimensions. 47 48 Note: Magnetisation is passed from 1H to 15N and then selectively to the carbonyl 49 13 15 13 50 C via the NH– CO J-coupling. Magnetisation is then passed back via 15 1 51 N to H for detection. 52 53 Source: [39]. See also: [18]. 54 55 227. homonuclear decoupling 56 decoupling 57 58 59 Spin decoupling in nuclear magnetic resonance spectroscopy between two signals of 60 the same nuclear isotope.

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1 2 3 Note: Homonuclear decoupling is normally performed through selective 4 excitation of specific NMR signals within a spectrum or through pure shift 5 6 experiments such as PSYCHE. 7 8 Source: [20]. See also: heteronuclear decoupling. 9 10 228. homonuclear Hartmann-Hahn spectroscopy, (HOHAHA) 11 12 13 See: total correlation spectroscopy. 14 15 229. imaginary NMR spectrum 16 imaginary spectrum 17 For Peer Review Only 18 In nuclear magnetic resonance spectroscopy one of two equally sized blocks of 19 frequency data 90° out of phase to each other produced by Fourier transformation of the 20 21 time domain signal. 22 23 Note 1: Usually the imaginary frequency data is not normally displayed and is used 24 for phase correction of the real spectrum. 25 26 Note 2: In simple 1D spectra this equates to the NMR signals being in dispersion 27 28 mode. 29 30 Source: [21]. 31 32 230. incredible natural-abundance double-quantum transfer experiment, 33 (INADEQUATE) 34 35 36 Nuclear magnetic resonance spectroscopy experiment designed to show homonuclear 37 spin-spin coupling correlations between low natural abundance nuclei such as 13C. 38 39 Note: 2D variant shows each coupled pair of nuclei gives a pair of peaks on the 40 INADEQUATE spectrum which both have the same vertical coordinate, 41 which is the sum of the chemical shifts of the nuclei; the horizontal 42 43 coordinate of each peak is the chemical shift for each of the nuclei 44 separately. 45 46 Source: [27]. 47 48 231. insensitive nuclei enhanced by polarization transfer, (INEPT) 49 50 51 Pulse sequence in nuclear magnetic resonance spectroscopy that involves the transfer 52 of nuclear spin polarization from spins with large Boltzmann population differences to 53 nuclear spins of interest with low Boltzmann population differences. 54 55 Note 1: INEPT uses spin-spin coupling for the polarization transfer in contrast to 56 nuclear Overhauser effect (NOE) which arises from dipolar cross- 57 58 relaxation. 59 60 Note 2: INEPT is a building block for many heteronuclear NMR experiments.

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1 2 3 Source: [27]. 4 5 6 232. inverse gated decoupling 7 8 See: gated decoupling. 9 10 233. inversion pulse 11 12 13 Pulse in nuclear magnetic resonance spectroscopy that completely inverts the 14 magnetisation of a spin e.g. +z to –z. 15 16 Note: The inversion pulse can be a simple 180°or composite pulse. 17 For Peer Review Only 18 234. inversion recovery sequence 19 20 inversion recovery 21 22 Spin echo sequence preceded by a 180° inversion pulse used to determine spin-lattice 23 relaxation times in nuclear magnetic resonance spectroscopy . 24 25 Note: The sequence is typically denoted as 180° – τ – 90°. 26 27 28 Source: [20]. See also: inversion time. 29 30 235. inversion time, (TI), TI 31 32 Time between the inversion pulse and the sampling pulse(s) in an inversion recovery 33 sequence. 34 35 36 Note: TI ,null is the value of TI when longitudinal magnetization (Mz) is close to 37 zero at the end of the TI interval. 38 39 236. J-modulated spin-echo, (J-MOD) 40 41 Nuclear magnetic resonance pulse sequence that refocuses spin vectors that have 42 43 fanned out due to field inhomogeneity or chemical shift differences. 44 45 Note: typically denoted as 90° - τ - 180° - τ (echo) 46 47 Source: [20]. See also: spin echo. 48 49 50 237. J-resolved spectroscopy, (J-RES) 51 52 Two-dimensional nuclear magnetic resonance spectroscopy resolving chemical shift 53 information in one dimension and spin-spin coupling in the second. 54 55 Note 1: J-RES exists as both homonuclear and heteronuclear variants 56 57 58 Note 2: The homonuclear variant can generate homonuclear decoupled projection 59 when processed with a tilt function. 60

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1 2 3 Source: [27]. 4 5 6 238. Knight shift 7 8 Frequency shift in the nuclear magnetic resonance spectrum of a paramagnetic species 9 that refers to the relative shift K in NMR frequency for atoms in a metal (e.g. sodium) 10 compared with the same atoms in a nonmetallic environment (e.g. as a salt). 11 12 13 Note: The observed shift reflects the local magnetic field produced at the metal 14 nucleus by the magnetization of the conduction electrons. 15 16 Source: [40]. 17 For Peer Review Only 18 239. Larmor angular frequency, ω, ω 19 L 20 Larmor frequency 21 22 Frequency at which nuclide with a nuclear spin precess around the direction of an 23 external magnetic induction B0. �L = ―��0 , where γ is the gyromagnetic ratio of the 24 nucleus. 25 26 27 Source: [3, 20]. 28 29 240. Larmor precession 30 31 Precession of the magnetic moment (M) of an object at an angular frequency, ωL, about 32 a static magnetic induction (B ), named after Joseph Larmor. 33 0 34 35 Note: Larmor precession can be visually compared to the precession of a tilted 36 gyroscope in an external torque-exerting gravitational field. 37 38 39 40 41 42 43 44 45 46 47 48 49 50 Source: [20]. 51 52 53 241. longitudinal relaxation 54 55 See: spin-lattice relaxation. 56 57 58 59 60

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1 2 3 242. magic angle spinning, (MAS) 4 5 6 Technique in solid-state nuclear magnetic resonance spectroscopy to remove or reduce 7 the influence of anisotropic interactions by rapid sample rotation about the magic 8 angle. 9 10 Note 1: Much like in the case of solutions, MAS effectively averages orientation- 11 dependent interactions and allow high resolution spectra. 12 13 14 Note 2: The rate of spinning must be greater than or equal to the magnitude of the 15 anisotropic interaction to average it to zero. 16 17 18 For Peer Review Only 19 20 21 22 23 24 25 26 27 where B0 is external magnetic induction and θ is the axis of rotation of the sample at an 28 angle of approx. 54.74° to the external magnetic induction. 29 30 Source: [21]. 31 32 243. magnetic dipole–dipole interaction in NMR 33 34 35 See: dipolar coupling in nuclear magnetic resonance spectroscopy. 36 37 244. magnetic flux density 38 39 See: static magnetic flux density 40 41 42 245. magnetogyric ratio 43 44 See: gyromagnetic ratio. 45 46 246. multiple-quantum magic angle spinning NMR, (MQMAS) 47 48 49 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy used to 50 obtain high-resolution NMR spectra of quadrupolar nuclei by removal of the anisotropy 51 of the quadrupole interaction, involving creating a triple-quantum (or 5Q) coherence. 52 53 Source: [41]. 54 55 56 247. multiplet 57 58 Feature in a nuclear magnetic resonance spectrum that is split but is too complex to 59 easily interpret. 60

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1 2 3 Note: A multiplet is distinguished from multiplicity of NMR peaks that give well- 4 resolved doublet, triplet, quartet, pentet etc. 5 6 7 248. multiplicity of NMR peaks 8 multiplicity 9 10 Splitting into more than one peak of an NMR signal due to interaction with other 11 magnetic vectors, normally adjacent nuclei. 12 13 14 Note 1: Multiplicity can arise from spin, spin (J) coupling and, in solids and 15 restrained media, dipolar coupling. 16 17 Note 2: InFor its simplest Peer form multiplicity Review results in Only patterns associated with the 18 2nI+1 rule (singlet, doublet, triplet, quartet, pentet etc.) although complex 19 multiplets arise through variation in spin-spin coupling constants and 20 21 second order multiplets exist where peak overlap occurs. 22 23 Source: [14]. 24 25 249. net dephasing time, T2* 26 T2-star 27 28 29 Measured time constant associated with spin-spin relaxation for loss of magnetization 30 in the xy plane. 31 32 Note: T2* includes losses due to B0 inhomogeneity as well as spin-spin relaxation 33 and is always less than or equal to the spin-lattice relaxation time (T2). 34 35 36 Source: [20], [42] p 2493. 37 38 250. non-uniform sampling, (NUS) 39 40 Technique employed within a high dimensionality nuclear magnetic resonance 41 spectroscopy experiment that acquires only a subset of the data points traditionally 42 43 acquired linearly thus enabling a reduction in experiment time or an increased 44 resolution in the resultant spectra. 45 46 Note: NUS uses reconstruction methods to allow the extraction of complete sets 47 of chemical shift information. 48 49 50 251. nuclear electric quadrupole moment, eQ 51 quadrupole moment of a nucleus 52 53 Parameter which describes the effective shape of the ellipsoid of nuclear charge 54 distribution. 55 56 Note 1: Non-zero quadrupole moment indicates that the charge distribution is not 57 58 spherically symmetric. 59 60

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1 2 3 Note 2: By convention, the value of eQ is taken to be positive if the ellipsoid is 4 prolate and negative if it is oblate. 5 6 7 Source: [43]. 8 9 252. nuclear magnetic resonance relaxometry, (NMRR) 10 relaxometry 11 12 13 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy to 14 measure nuclear relaxation variables. 15 16 Note: NMRR generally involves analysis of time domain NMR signals to 17 generateFor simplifiedPeer NMR Review data rather than Only conventional full frequency 18 resolved NMR spectra. 19 20 21 253. nuclear magnetic resonance spectrum 22 NMR spectrum 23 24 Representation of nuclear magnetic resonance spectroscopy data with at least one 25 dimension a frequency domain. 26 27 28 Note: An NMR spectrum typically involves the Fourier transform of a free 29 induction decay. See Fourier-transform spectroscopy. 30 31 254. nuclear Overhauser effect, (nOe, NOE), η 32 33 Change of intensity of one resonance when the spin transitions of another are somehow 34 35 perturbed from their equilibrium populations. 36 37 Note 1: The nuclear Overhauser effect at nucleus i for perturbation of spin S is 38 expressed as a relative intensity change between the equilibrium intensity 39 (I) and that in the presence of the nOe (I ). � (S) = (� ― �o) � . The effect 40 o � o 41 may be given as a percentage η ×100 %. 42 43 Note 2: nOe allows a measure of through space rather than through bond 44 interactions between nuclei and is proportional to the inverse 6th power of 45 the internuclear distance. 46 47 48 Note 3: η can be positive or negative depending on the motional properties of the 49 molecule and the signs of the gyromagnetic ratios. 50 51 Source: [21], [42]. 52 53 255. nuclear Overhauser effect difference spectroscopy, 54 55 nOe difference spectroscopy 56 57 One dimensional nuclear magnetic resonance spectroscopy that yields, through 58 subtraction of spectra generated with and without selective excitation of a specific 59 60

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1 2 3 resonance, the nuclear Overhauser enhancement of nuclei spatially close to a 4 selectively excited nucleus. 5 6 7 Source: [27]. 8 9 256. nuclear Overhauser effect spectroscopy, (NOESY) 10 nuclear Overhauser enhancement spectroscopy 11 12 13 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy based on 14 the nuclear Overhauser effect to observe nuclei that are close to each other in space. 15 16 Note 1: NOESY is typically run as a homonuclear 1H experiment. 17 For Peer Review Only 18 Note 2: A NOESY spectrum yields through space correlations via dipolar cross- 19 relaxation. 20 21 22 Note 3: For small molecules, NOE may be observed between protons that are up to 23 0.4 nm apart, while the upper limit for large molecules is about 0.5 nm. 24 25 Note 4: NOESY also detects chemical and conformational exchange, when it is 26 termed exchange spectroscopy (EXSY). 27 28 29 Source: [27]. 30 31 257. nuclear quadrupole resonance spectroscopy, (NQR) 32 33 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy where 34 35 splitting of the nuclear spin states is determined by the electrostatic interaction of the 36 nuclear charge density with the external electric potential of the surrounding electron 37 cloud. 38 39 Note: Unlike NMR, NQR transitions of nuclei can be detected in the absence of a 40 magnetic field. 41 42 43 Source: [43]. 44 45 258. nuclear spin 46 47 See: spin of a nucleus. 48 49 50 259. observation frequency 51 52 Frequency corresponding to the centre of the spectrum window for a given nucleus 53 under observation and the nominal frequency used to generate the hard, full spectrum 54 pulses. 55 56 Source: [14]. 57 58 59 60

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1 2 3 260. Pake doublet 4 5 6 Characteristic line shape seen in solid-state nuclear magnetic resonance spectroscopy 7 arising from dipolar coupling between two nuclei. 8 9 10 11 12 13 14 15 16 17 18 For Peer Review Only 19 20 21 22 23 261. phase correction 24 25 Linear combination of the real and imaginary parts of a 1-D nuclear magnetic 26 resonance spectrum to produce peaks with pure absorption mode line shape. 27 28 29 Note: The phase correction is normally described by the automatic or manual 30 setting of a fixed zero order and a frequency dependent first order phase 31 constant. 32 33 Source: [21]. 34 35 36 262. phase cycling 37 38 Component of nuclear magnetic resonance spectroscopy experiment that repeats a 39 pulse sequence changing only the phases of the pulse(s) and the phase-sensitive 40 detector reference. 41 42 Note: the resultant FID's are then added to suppress undesirable signal 43 44 components and/or to produce the desired effect of a pulse sequence (e.g., 45 multiple quantum filter) 46 47 Source: [20]. 48 49 263. powder pattern 50 51 52 Very broad and distinctive line shape seen in a static solid-state nuclear magnetic 53 resonance spectroscopy experiment with a typical magnitude of 102 – 105 Hz. 54 55 Note: A powder pattern is a summation of the multitude of signals arising from 56 crystals with different orientations within the magnetic induction. 57 58 59 60

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 For Peer Review Only 19 264. precession 20 21 Classical description of the behaviour of nuclear magnetic moments, in which the 22 vectors rotate about the B0 axis at their Larmor angular frequencies. 23 24 25 Source: [21]. 26 27 265. presaturation 28 29 Technique to suppress a particular nuclear magnetic resonance spectroscopy signal 30 where a long low-power pulse is applied to that specific resonance prior to the main 31 pulse sequence. 32 33 34 Note: Presaturation is typically used as a method for solvent suppression. 35 36 Source: [27]. 37 38 266. pulse sequence 39 40 41 Timed series of radiofrequency pulses and magnetic field gradients that define a part or 42 whole of a nuclear magnetic resonance spectroscopy experiment. 43 44 267. pulsed-field gradient, (PFG) 45 gradient pulse 46 47 48 Short, timed pulse in nuclear magnetic resonance spectroscopy that momentarily 49 destroys the magnetic field homogeneity within the sample through a spatial-dependent 50 field intensity. 51 52 Note 1: The net result of the pulse is that spins are dispersed in the transverse plane 53 (defocussed) and produce zero net magnetization. 54 55 56 Note 2: A PFG is characterized by its power, shape, duration and axis. 57 58 Note 3: PFG techniques are used in magnetic resonance imaging, spatially-selective 59 NMR, and diffusion ordered NMR spectroscopy (DOSY). 60

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1 2 3 Source: [21]. 4 5 6 268. pure shift yielded by chirp excitation, (PSYCHE) 7 8 Nuclear magnetic resonance spectroscopy experiment generating homonuclear spin- 9 spin decoupled spectra. 10 11 Note: The effect is achieved through the concatenation of partial free induction 12 13 decays generated with a series of swept adiabatic pulses. 14 15 Example: 1H spectrum with no 1H,1H coupling. 16 17 Source: [44]. 18 For Peer Review Only 19 269. quadrature detection in nuclear magnetic resonance spectroscopy 20 21 22 Collection of time domain nuclear magnetic resonance spectroscopy data on both the x 23 and y axes of the rotating frame of reference to allow discrimination of positive and 24 negative frequencies. 25 26 Source: [21]. 27 28 29 270. quadrupole moment of a nucleus 30 31 See: nuclear electric quadrupole moment. 32 33 271. quadrupolar nuclide 34 35 36 Nuclide with spin quantum number I > ½ and a non-spherical distribution of charge in 37 the nucleus giving rise to a nuclear electric quadrupole moment (eQ). 38 39 272. quadrupolar relaxation 40 41 Relaxation mechanism in nuclear magnetic resonance spectroscopy arising from 42 intramolecular quadrupolar interactions with electric field gradients. 43 44 45 Source: [20]. See also: quadrupolar nuclide. 46 47 273. radiation damping 48 49 Line-broadening effect on intense signals in high field nuclear magnetic resonance 50 51 spectroscopy. 52 53 Note 1: Radiation damping occurs when the rotating transverse magnetization of the 54 sample is intense enough to induce large enough electromotive force in the 55 radiofrequency coil strong enough that it feedbacks to the sample. This 56 causes a rotation of magnetisation back to the +z axis and result in line- 57 broadening of the intense peak. 58 59 60

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1 2 3 Note 2: Radiation damping can also produce other effects including changes to 4 amplitude and phase of adjacent peaks. 5 6 7 Source: [27]. 8 9 274. radiofrequency (RF) coil 10 11 In nuclear magnetic resonance spectroscopy, an inductor-capacitor resonant circuit 12 13 used to set up B1 magnetic inductions in a sample and to detect the signal from the 14 sample. 15 16 275. real spectrum 17 For Peer Review Only 18 In nuclear magnetic resonance spectroscopy, one of two equally sized blocks of 19 frequency data 90° out of phase to each other produced by Fourier transformation of the 20 21 time domain signal. 22 23 Note: Usually only the real frequency data is displayed and in simple 1D spectra 24 equates to the NMR signals being absorption mode (in-phase). 25 26 Source: [21]. See also: imaginary spectrum, Fourier-transform spectroscopy. 27 28 29 276. relaxation reagent 30 31 Paramagnetic species added to a sample in a nuclear magnetic resonance spectroscopy 32 experiment to promote more rapid spin-lattice relaxation and allow a faster pulse 33 repetition rate. 34 35 36 Example: Chromium(III) acetyl acetonate, Cr(acac)3 is typically used. 37 38 Source: [14]. 39 40 277. relaxometry 41 42 See: nuclear magnetic resonance relaxometry. 43 44 45 278. repetition time, (TR), Tr 46 47 Time duration between repetitions of a nuclear magnetic resonance pulse sequence 48 including the pulse sequence, acquisition time and relaxation delay. 49 50 51 Source: [21]. 52 53 279. residual dipolar coupling, (RDC) 54 55 Dipolar coupling, but of a reduced magnitude to that seen in solids, observed in a liquid 56 sample between spins in a molecule where there is incomplete averaging of spatially 57 anisotropic dipolar couplings. 58 59 60

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1 2 3 Note 1: RDC is typically achieved through partial alignment of molecules in the 4 liquid state through spatially aligned gels or liquids. 5 6 7 Note 2: RDC is used to provide 3D structural information on molecules. 8 9 280. rotating-frame NOE spectroscopy, (ROESY) 10 cross-relaxation appropriate for minimolecules emulated by locked spins 11 (CAMELPSIN) 12 13 14 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy yielding 15 through-space correlations via spin-spin relaxation. 16 17 Note 1: ROESYFor isPeer similar to theReview NOESY experiment Only (see: nuclear Overhauser 18 effect spectroscopy) and is useful for determining which signals arise from 19 protons that are close to each other in space even if they are not bonded. 20 21 22 Note 2: ROESY has the advantage over the NOESY experiment that its response 23 does not go through a null at specific correlation times and is thus preferred 24 for molecules having molecular masses of a few thousand Da. 25 26 Source: [27]. 27 28 29 281. rotational echo double resonance, (REDOR) 30 31 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy allowing 32 recoupling of heteronuclear dipolar coupling under magic angle spinning. 33 34 Source: [45]. 35 36 37 282. saturation transfer difference spectroscopy, (STD) 38 39 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy that 40 allows detection of transient binding of small molecule ligands to macromolecular 41 receptors. 42 43 –3 –8 44 Note: Range of applicable dissociation constants is approximately 10 to 10 M. 45 The experiment relies on ligand-signal attenuation through spin diffusion 46 saturation propagating from the macromolecule. 47 48 Source: [46]. 49 50 51 283. selective decoupling 52 53 Spin decoupling of a specific resonance by selective irradiation. 54 55 284. selective excitation 56 selective irradiation 57 58 59 Application of a frequency selective radiofrequency pulse(s) to a single resonance or a 60 discreet band of frequencies.

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1 2 3 Note: Selective excitation is usually achieved through the application of long, low 4 power (soft) pulses. 5 6 7 Source: [21]. 8 9 285. selective pulse 10 11 Radiofrequency pulse with a narrow frequency spectral bandwidth (long, low-power 12 13 pulse) to excite nuclei in a limited chemical shift range (see selective excitation). 14 15 Source: [14]. 16 17 286. single crystal nuclear magnetic resonance spectroscopy 18 For Peer Review Only 19 Solid-state nuclear magnetic resonance spectroscopy on a single crystal in a similar 20 21 manner to that used in X-ray diffraction. 22 23 Note: A large crystal is mounted on a ‘tenon’, which is in turn mounted on a 24 goniometer head. If the orientation of the unit cell is known with respect to 25 the tenon, then it is possible to determine the orientation of the NMR 26 interaction tensors with respect to the molecular frame. 27 28 29 Source: [47]. 30 31 287. solid-state nuclear magnetic resonance spectroscopy, (SSNMR) 32 33 Application of nuclear magnetic resonance spectroscopy to solids. 34 35 36 Note: SSNMR is characterised by the presence of anisotropic (directionally 37 dependent) interactions. Chemical shift anisotropy (CSA) and internuclear 38 dipolar coupling result in severe line-broadening of the corresponding NMR 39 signals and specific hardware and methods are required to perform SSNMR 40 to mitigate some of these issues including magic angle spinning (MAS). 41 42 Source: [22]. 43 44 45 288. solvent suppression 46 47 In nuclear magnetic resonance spectroscopy reduction or removal of large, unwanted 48 resonances from solvents to improve spectrum quality and dynamic range through 49 selective excitation and exploiting differences in relaxation times between solvent and 50 51 analyte signals. 52 53 Source: [20]. 54 55 289. spectral width in NMR, fSW 56 spectral width 57 58 Frequency range that describes the width of the spectrum window of a specific nucleus 59 60 in nuclear magnetic resonance spectroscopy.

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1 2 3 290. spin of a nucleus 4 nuclear spin 5 6 spin 7 8 Intrinsic angular momentum of a nucleus (or other sub-atomic particle). 9 10 Note 1: The magnitude of nuclear spin is (ℎ 2�) �(� + 1) where I is the spin 11 12 quantum number and h is the Planck constant. 13 14 Note 2: In nuclear magnetic resonance spectroscopy, only nuclei with spin I > 0 are 15 observable. 16 17 Note 3: The spin of a nucleus is dependent on the numbers and alignments of the 18 For Peer Review Only 19 spins of its individual protons and neutrons. 20 21 Note 4: Nuclei with a spin of ½ generate the simplest nuclear magnetic resonance 22 spectra and are thus the most commonly studied. 23 24 Source: [31]. 25 26 27 291. spin decoupling 28 29 Irradiation of a nucleus in nuclear magnetic resonance spectroscopy to prevent spin- 30 spin coupling. 31 32 See also: homonuclear decoupling, heteronuclear decoupling. 33 34 35 292. spin echo, (SE) 36 Hahn echo 37 38 Refocusing of spin magnetisation usually by 2 consecutive radiofrequency pulses. 39 40 41 Note 1: The simplest form of the spin-echo pulse sequence consists of 90°-pulse, a 42 180°-pulse, and then an echo. The time between the middle of the first RF 43 pulse and the peak of the spin echo is called the echo time. 44 45 Note 2: SE is typically used within a pulse sequence to refocus chemical shift by 46 pulses 90° TE/2 180° TE/2. (See also: flip angle.) 47 48 49 Source: [21]. 50 51 293. spin system 52 53 Group of magnetic nuclei that interact amongst themselves through spin-spin coupling 54 but do not interact with any nuclei outside the spin system. 55 56 57 Source: [48]. 58 59 60

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1 2 3 294. spin-lattice relaxation 4 longitudinal relaxation 5 6 T1 relaxation 7 T1 relaxation 8 9 Mechanism in nuclear magnetic resonance spectroscopy by which the component of 10 the magnetization vector along the direction of the static magnetic induction reaches 11 thermodynamic equilibrium with its surroundings through loss of energy of the excited 12 13 nuclear spins to the surrounding molecular lattice. The resultant exponential decay of 14 signal is characterised by the spin-lattice relaxation time T1 (reciprocal of the rate 15 constant of this mechanism). 16 17 Note: TFor1 dictates Peer the time required Review between individual Only NMR scans to ensure the 18 system has returned to equilibrium. 19 20 21 Source: [14]. See also: spin-lattice relaxation time. 22 23 295. spin-lattice relaxation time, T1 24 spin-lattice time constant 25 26 Reciprocal of the rate constant of longitudinal relaxation. 27 28 29 See also: spin-spin relaxation time, net dephasing time. 30 31 296. spinning sidebands 32 33 Satellite peaks in a nuclear magnetic resonance spectrum symetrically spaced either 34 side of a main peak at a frequency offset related to the rate of spinning of the sample. 35 36 37 Note: In solid state nuclear magnetic resonance spectroscopy this occurs if the 38 sample is spun at a rate less than the magnitude of the anisotropic 39 interaction, 40 41 Source: [48]. 42 43 44 297. spin-spin coupling 45 spin coupling 46 47 Effect of the relative orientation of the magnetic fields of adjacent nuclei on each other 48 and the resultant splitting of their signals in nuclear magnetic resonance spectroscopy 49 (multiplicity). 50 51 52 Note 1: For 2 proximal nuclei A and B, magnetic field at nucleus A = nuclear 53 shielding + magnetic field at nucleus B. If nucleus B has two possible 54 orientations in field due to spin ½ then nucleus A will experience 2 possible 55 magnetic fields and therefore give 2 distinct frequencies. The frequency 56 difference between these two lines is called the spin-spin coupling constant 57 58 JAB. 59 60

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1 2 3 Note 2: Spin-spin coupling is transmitted through intervening bonding electrons, in 4 contrast to the through space dipolar mechanism. 5 6 7 Note 3: SI unit: Hz. 8 9 Source: [14]. 10 11 298. spin-spin coupling constant, J 12 13 coupling constant 14 15 Frequency difference between two nuclear magnetic resonance lines arising from spin- 16 spin coupling. 17 For Peer Review Only 18 Note: Parentheses may be used (for example) to indicate the species of nuclei 19 coupled, e.g. J(13C, 1H) or, additionally, the coupling path, e.g. J(POCF). 20 21 Where no ambiguity arises, the elements involved can be, alternatively, 22 given as subscripts, e.g. JCH. The nucleus of higher mass should be given 23 first. nJ indicates coupling through n bonds. 24 25 Source: [42] p 2592. 26 27 28 299. spin-spin relaxation 29 transverse relaxation 30 T2 relaxation 31 32 Loss of magnetization in the xy plane (in the absence of B0 inhomogeneities) through 33 the interchange of energy between nuclear spins resulting in some precessing faster 34 than the Larmor frequency and some slower. 35 36 37 Note: The resultant exponential decay of signal is characterised by the spin-spin 38 relaxation time T2 (reciprocal of the rate constant of this mechanism). 39 40 Source: [14]. See also: net dephasing time. 41 42 43 300. spin-spin relaxation time, T2 44 transverse relaxation time 45 46 Reciprocal of the rate constant of spin-spin relaxation. 47 48 Source: [42] p 2493. See also: spin-lattice relaxation time, net dephasing time. 49 50 51 301. static magnetic flux density, B0 52 magnetic flux density 53 static magnetic field 54 55 Flux density of the magnetic field of a nuclear magnetic resonance spectrometer about 56 whose direction the nuclear magnetic moment precesses. 57 58 59 Note 1: Magnitude of B0 is expressed in Tesla or as the nominal proton precession 60 frequency (e.g., 14 T or 600 MHz).

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1 2 3 Note 2: Static magnetic induction is related to the magnetic field H through the 4 equation B = μH where μ is the permeability of the material. 5 6 7 Source: [20], [42] p 2492, [3] p17. 8 9 302. symmetrisation 10 11 Method of removing artefacts from a two-dimensional nuclear magnetic resonance 12 13 spectrum that are symmetrical about the diagonal (e.g. HH COSY) or the f1 axis (e.g. 14 tilted J-resolved spectra). Values equidistant from midline are compared and replaced 15 the lower (or average) value of the two. 16 17 Source: [21]. 18 For Peer Review Only 19 303. t in two-dimensional nuclear magnetic resonance spectroscopy 20 1 21 t1 in 2-D NMR 22 23 Time domain arising from the regular increments of the delay period in two- 24 dimensional nuclear magnetic resonance spectroscopy. 25 26 304. t in two-dimensional nuclear magnetic resonance spectroscopy 27 2 28 t2 in 2-D NMR 29 30 Time domain in two-dimensional nuclear magnetic resonance spectroscopy arising 31 from direct free induction decay detection. 32 33 305. t1 noise in two-dimensional nuclear magnetic resonance spectroscopy 34 t noise in 2-D NMR 35 1 36 37 Streaks of spurious artefact signals in a two-dimensional nuclear magnetic resonance 38 spectrum parallel to the f1 axis at the f2 of a strong resonance. 39 40 Source: [21]. 41 42 43 306. T1 relaxation 44 45 See: spin-lattice relaxation. 46 47 307. T2 relaxation 48 49 50 See: spin-spin relaxation. 51 52 308. three-dimensional nuclear magnetic resonance spectroscopy 53 3-D NMR 54 55 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy in which 56 data are collected in three time domains. 57 58 59 60

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1 2 3 Note: A 3-D NMR experiment may be constructed from a 2-D NMR experiment 4 by inserting an additional indirect evolution time and a second mixing 5 6 period between the first mixing period and the direct data acquisition. 7 8 See also: triple-resonance nuclear magnetic resonance spectroscopy. 9 10 309. time domain 11 12 13 Condition in nuclear magnetic resonance spectroscopy where the independent variable 14 of all functions is time. 15 16 Example: The display of an FID. 17 For Peer Review Only 18 Source: [14]. 19 20 21 310. time domain nuclear magnetic resonance spectroscopy, (TD-NMR) 22 23 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy run at 24 low magnetic field strengths where data analysis is performed directly on the free 25 induction decay, often through the extraction of relaxation time constants 26 27 28 See also: relaxometry. 29 30 311. tip angle 31 32 See: flip angle. 33 34 35 312. total correlation spectroscopy, (TOCSY) 36 homonuclear Hartmann-Hahn spectroscopy, (HOHAHA) 37 38 Two-dimensional nuclear magnetic resonance homonuclear correlation experiment, 39 which creates correlations between all protons within a given spin system, not just 40 between geminal or vicinal protons as in COSY. 41 42 43 Note: TOCSY uses a spin lock to allow propagation of magnetisation through 44 scalar couplings. 45 46 Source: [27]. 47 48 313. total suppression of spinning sidebands, (TOSS) 49 50 51 Technique to suppress spinning sidebands in solid-state nuclear magnetic resonance 52 spectroscopy with cross polarisation in magic angle spinning experiments. 53 54 Source: [27]. 55 56 314. transverse relaxation 57 58 59 See: spin-spin relaxation. 60

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1 2 3 315. transverse relaxation optimized spectroscopy, (TROSY) 4 5 6 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy, usually 7 in protein NMR, that improves peak sharpness for molecules having a molar mass of 8 greater than 100 kDa. 9 10 Note: TROOSY relies on the cancellation of the dipolar coupling and chemical 11 shift anisotropy (CSA) components of the transverse relaxation (See: spin- 12 13 spin relaxation). 14 15 Source: [25]. 16 17 316. transverse relaxation time 18 For Peer Review Only 19 See: spin-spin relaxation time. 20 21 22 317. triple-resonance nuclear magnetic resonance spectroscopy 23 triple-resonance NMR 24 25 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy using 26 three NMR-active nuclei. 27 28 1 13 15 29 Note: For proteins the three nuclei are usually H hydrogen, C carbon and N 30 nitrogen which requires suitable labelling of the sample. 31 32 318. two-dimensional nuclear magnetic resonance spectroscopy 33 2-D NMR 34 35 36 Measurement method [VIM 2.5] of nuclear magnetic resonance spectroscopy in which 37 data are collected in two time domains: acquisition of the free induction decay (t2) and a 38 successively incremented delay (t1). 39 40 Note: The resulting data matrix is subjected to two successive Fourier transforms 41 to produce a spectrum with two frequency axes, usually either chemical 42 43 shift/chemical shift (correlation spectroscopy) or chemical shift/J-coupling 44 (See: J-resolved spectroscopy). 45 46 Source: [20]. 47 48 319. WALTZ decoupling 49 50 51 See: wideband, alternating-phase, low-power technique for residual splitting. 52 53 320. wideband, alternating-phase, low-power technique for residual splitting 54 WALTZ decoupling 55 56 Cluster of pulses applied repeatedly to heteronuclear decoupling. 57 58 59 Note: WALTZ is commonly used for proton decoupling during the acquisition of 60 13C spectra.

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1 2 3 Source: [21]. 4 5 6 321. Zeeman levels 7 8 Energy levels of a nucleus arising from the interaction of its magnetic dipole with an 9 external magnetic field. 10 11 Source: [20]. 12 13 14 322. zero-field nuclear magnetic resonance spectroscopy 15 zero-field NMR 16 17 MeasurementFor method Peer[VIM 2.5] ofReview nuclear magnetic Only resonance spectroscopy in which 18 nuclear magnetic resonance spectra are acquired in an environment carefully screened 19 from magnetic fields, including from the Earth’s field allowing the direct detection of J- 20 21 spectra in the absence of Zeeman interactions (See: Zeeman levels). 22 23 Source: [49]. 24 25 ATOMIC SPECTROSCOPY 26 27 28 In optical spectroscopy, energy absorbed to move an electron to a higher energy level 29 and/or the energy emitted as the electron moves to a lower energy level is absorbed or 30 emitted in the form of photons. Because each element has a unique number of 31 electrons, an atom will absorb/release energy in a pattern unique to its elemental 32 identity (e.g. Ca, Na, etc.) and thus will absorb/emit photons in a correspondingly 33 unique pattern. The type of atoms present in a sample, or the amount of atoms present 34 in a sample can be deduced from measuring these changes in light wavelength and light 35 36 intensity. In this section, optical spectroscopy terms are provided for atomic emission, 37 atomic absorption and atomic fluorescence spectroscopies 38 An encyclopedia of spectroscopy and spectrometry was published in 2016 which has 39 inspired many definitions here [31]. 40 41 323. ablation by sputtering 42 43 44 Bombardment of a sample surface with ions resulting in the removal of atoms from 45 their lattice sites, and thus an ongoing discharge process which causes continuous 46 ablation of the sample. 47 48 Source: [50]. 49 50 324. ablation efficiency in LIBS 51 52 53 Mass of sample removed in laser-induced breakdown spectroscopy divided by the 54 energy delivered by the laser beam. 55 56 Source: [51]. 57 58 59 60

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1 2 3 325. ablation rate 4 5 6 Depth of sample layer removed in the glow discharge process per unit time. 7 8 Note: Ablation rate is usually expressed in nm s−1. 9 10 Source: [50]. 11 12 13 326. ablation threshold fluence in LIBS 14 15 Minimum fluence required to achieve ablation of the sample. 16 17 Source: [51]. 18 For Peer Review Only 19 20 327. absorption path-length 21 22 Path-length of a beam of radiation in an absorbing medium. 23 24 Source: [10]. 25 26 27 328. acid transient effects in ICP spectrometry 28 29 Increase in the signal equilibration time or in the wash out time caused by a 30 modification in the inorganic acid concentration. 31 32 Source: [52]. 33 34 35 329. additional gases in flame atomic spectroscopy 36 37 Gases added to a combustion mixture. 38 39 Note: An inert diluent is non-reactive, an auxiliary gas is reactive. 40 41 42 Source: [10]. 43 44 330. aerosol 45 46 Sol in which the dispersed phase is a solid, a liquid or a mixture of both and the 47 continuous phase is a gas (usually air). 48 49 50 Note 1: Owing to their size, the particles of the dispersed phase have a 51 comparatively small settling velocity and hence exhibit some degree of 52 stability in the earth s gravitational field. 53 54 Note 2: An aerosol can be characterized by its chemical composition, its 55 radioactivity (if any), the particle size distribution, the electrical charge and 56 57 the optical properties. 58 59 Note 3: In inductively-coupled plasma spectrometry the sample is delivered to the 60 plasma as an aerosol, where the continuous gas phase is argon.

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1 2 3 Source: [53] p 1805. 4 5 6 331. aerosol transport phenomena in ICP spectrometry 7 8 Processes occurring inside the spray chamber or desolvation system responsible for the 9 modification of the primary aerosol to finally yield the tertiary aerosol. 10 11 Note: These phenomena include solvent evaporation, droplet coalescence or 12 13 coagulation, inertial droplet losses, gravitational settling and turbulence 14 losses. 15 16 Source: [52]. 17 For Peer Review Only 18 332. analyte transport rate in ICP spectrometry 19 20 21 Mass of analyte reaching the plasma per unit time. 22 23 Source: [52]. 24 25 333. atomic absorption spectroscopy, (AAS) 26 27 28 Measurement method [VIM 2.5] of atomic spectroscopy for measuring the amount of a 29 chemical element based on the measurement of the absorption of characteristic 30 electromagnetic radiation by atoms in the vapour phase. 31 32 Source: [31]. 33 34 35 334. atomic emission spectroscopy, (AES) 36 37 Measurement method [VIM 2.5] of atomic spectroscopy for measuring the amount of a 38 chemical element based on the measurement of the intensity of characteristic 39 electromagnetic radiation emitted by atoms or molecules. 40 41 Source: [31]. 42 43 44 335. atomic excitation source 45 excitation source 46 47 Atomizer intended to convert free atoms to an excited state. 48 49 50 Source: [10] 51 52 336. atomic fluorescence spectroscopy, (AFS) 53 54 Measurement method [VIM 2.5] of atomic spectroscopy for measuring the amount of a 55 chemical element based on the measurement of the re-emission of characteristic 56 electromagnetic radiation by atoms, following the absorption of radiation in the vapour 57 58 phase. 59 60

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1 2 3 Note: The wavelengths of the absorbed and re-emitted radiation may be identical 4 (atomic resonance fluorescence spectroscopy) or different. 5 6 7 Source: [31]. 8 9 337. atomic vapour 10 11 Vapour containing free atoms of analyte. 12 13 14 Source: [10]. 15 16 338. atomization 17 For Peer Review Only 18 Conversion to an atomic vapour. 19 20 21 Source: [10]. 22 23 339. atomization curve in electrothermal AAS 24 25 Graph of absorption against atomization temperature. 26 27 28 Source: [54]. 29 30 340. atomizer 31 32 Device used in atomic spectroscopy to achieve atomization. 33 34 35 Note: Examples are a flame or electrothermal atomizer. 36 37 Source: [10]. 38 39 341. Auger electron 40 41 42 Secondary electron ejected from an atom as a form of energy release (as opposed to 43 energy release more typically in the form of photon emission), following ejection of a 44 core shell electron and the resulting transition of an electron from a higher energy level 45 into the vacancy. 46 47 Source: [55]. 48 49 50 342. Auger spectroscopy 51 Auger electron spectroscopy, (AES) 52 53 Measurement method [VIM 2.5] of electron emission spectroscopy that utilizes Auger 54 electrons emitted from the target following excitation with an electron beam or 55 synchrotron X-ray beam (X-ray excited Auger electron spectroscopy). 56 57 58 Note 1: Chemical species are identified from the energies of the emitted Auger 59 electrons, and the typically low energies of the emitted electrons and 60

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1 2 3 resulting escape depth mean the technique is particularly sensitive for 4 surface species analysis. 5 6 7 Note 2: Most AES is performed under high or ultra-high-vacuum. 8 9 Source: [55]. 10 11 343. axial viewing mode 12 13 14 Inductively-coupled plasma optical emission spectrometer configuration in which the 15 entrance slit is aligned with the main plasma axis. 16 17 Note 1: TheFor large Peeramount of lightReview captured in this Only method, includes information 18 from the sample of interest plus background which can be considerable. 19 20 21 Note 2: Matrix interferences, which originate in the cooler plasma tail, can degrade 22 precision and accuracy. 23 24 Source: [52]. 25 26 344. background continuum emission in LIBS 27 28 29 Intense continuous background usually observed in laser-induced breakdown spectra 30 31 Note: The continuum emission originates from Bremsstrahlung radiation, which 32 predominates the first part of the plasma life time and decreases with 33 further plasma evolution. 34 35 36 Source: [51]. 37 38 345. background equivalent concentration, cBE 39 40 41 Concentration of a given element measured at a given wavelength providing the same 42 intensity as the background. 43 44 Source: [52]. 45 46 346. breakdown threshold fluence in LIBS 47 48 49 Minimum fluence required to achieve measurable emission signals 50 51 Note: Usually the breakdown-threshold fluence is orders of magnitude higher than 52 the ablation-threshold fluence. 53 54 Source: [51]. 55 56 57 347. Bremsstrahlung emission 58 59 Portion of the continuum spectrum originating from the energy lost by high velocity 60 electrons as they interact with positively charged ions without combining with them.

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1 2 3 Source: [52]. 4 5 6 348. Bremsstrahlung radiation 7 8 Photons with a broad energy distribution produced by losses in kinetic energy due to 9 the deceleration of charged particles connected with the emission of electromagnetic 10 radiation. 11 12 13 Source: [51]. 14 15 349. capacitive microwave plasma 16 17 Plasma generated by a capacitor in presence of a microwave field. 18 For Peer Review Only 19 Source: [52]. 20 21 22 350. characteristic line 23 24 Spectral line of an atom used for the measurement of analyte concentration by atomic 25 spectroscopy. 26 27 28 Note: Characteristic lines include resonance and non-resonance lines. 29 30 Source: [10]. 31 32 351. chemical modifier for electrothermal AAS 33 34 35 Substance added to an electrothermal atomizer to obtain a better analyte atomization, or 36 to alter the vaporization and/or atomization of interferents, thus mitigating 37 interferences. 38 39 Source:[54]. 40 41 352. continuum source in atomic spectroscopy 42 43 44 Source that emits electromagnetic radiation with relatively constant intensity over a 45 broad spectral region. 46 47 Note: The use of such a source allows for correction of spectral interferences. 48 49 50 Source: [54, 56]. 51 52 353. depth resolution 53 54 Capability to distinguish between two consecutive layers in a layered material. 55 56 57 Note 1: With GD-OES nanometre or even atomic-layer depth resolution can be 58 obtained. 59 60

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1 2 3 Note 2: usually the parameters used in the sputtering process (discharge parameters, 4 selected gas and pressure) restrict the achievable depth resolution. 5 6 7 Source: [50]. 8 9 354. depth-profiling 10 11 Process by which, using suitable conditions, the sample is sputtered ‘atomic layer by 12 13 layer’. 14 15 Note 1: Depth profile analysis can be accomplished by time resolved measurement 16 of the generated emission signals 17 For Peer Review Only 18 Note 2: Depth profiling using signal versus time measurement requires knowledge 19 of the ablation rate, which must be known, or has to be calculated, from 20 21 measurements of suitable materials. 22 23 Source: [50]. 24 25 355. desolvation in atomic spectroscopy 26 desolvation 27 28 29 Removal of the solvent in atomic spectroscopy, giving rise to particles of the solute 30 either in the solid or gas phase. 31 32 Source: [10]. 33 34 35 356. detection efficiency in ICP spectrometry 36 37 Probability that a given atom in the plasma probed volume generates a detectable 38 signal. 39 40 Source: [52]. 41 42 43 357. direct current glow discharge optical emission spectroscopy, (DC GD- 44 OES) 45 46 Measurement method [VIM 2.5] using optical emission spectroscopy in which 47 atomization and excitation occur in a glow electrical discharge sustained by a direct 48 current electric field. 49 50 51 Note 1: Generated argon ions impact with high energy on to the surface of the 52 cathode, which can thus be ablated in a purely mechanical way (cathodic 53 sputtering) or the cathode can be heated to assist evaporation (thermal 54 volatilization). 55 56 Note 2: DC GD-OES is only applicable for electrically conducting samples. 57 58 59 Source: [50]. 60

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1 2 3 358. direct-injection burner 4 5 6 Burner in a flame atomic spectrometer in which the fuel, the oxidant and the sample 7 solution are injected into the flame. (See: flame in flame atomic spectroscopy). 8 9 Note: This burner generally produces a turbulent flame (See: flame in flame 10 atomic spectroscopy). 11 12 13 Source: [10]. 14 15 359. discharge 16 17 See: electric discharge. 18 For Peer Review Only 19 360. dispersion of a sample in atomic spectroscopy 20 21 22 Conversion of the whole or part of a liquid or solid sample into a physical form 23 sufficiently finely divided to allow it to be atomized (see atomization) upon 24 introduction into the atomizer. 25 26 Source: [10]. 27 28 29 361. double-pulse laser-induced breakdown spectroscopy 30 31 Measurement method [VIM 2.5] of laser-induced breakdown spectroscopy in which 32 reactions are induced by the interaction of the evolved plasma and the remaining part of 33 the laser pulse, or with a following laser pulse provided from a second laser system. 34 35 36 Source: [51]. 37 38 362. dual viewing mode 39 40 Inductively coupled plasma spectrometer which allows axial viewing mode or radial 41 viewing mode. 42 43 44 Source: [52]. 45 46 363. Echelle spectrometer 47 48 See: GD-OES spectrometers with simultaneous detection. 49 50 51 364. electric discharge 52 discharge 53 54 Transmission of electrical current by a plasma in an applied electric field through a 55 normally non-conducting medium. 56 57 58 Note: An inductively-coupled plasma is a kind of electric discharge. 59 60

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1 2 3 365. electron number density 4 5 6 Number of free electrons in vapour phase per volume unit. 7 8 Note: SI unit: m−3 9 10 Source: [57]. 11 12 13 366. electron spectroscopy for chemical analysis, (ESCA) 14 15 See: X-ray photoelectron spectroscopy. 16 17 367. electrothermal atomic absorption spectroscopy, (ETAAS) 18 For Peer Review Only 19 20 Measurement method [VIM 2.5] of atomic absorption spectroscopy in which the 21 sample is atomized by an electrothermal atomizer. 22 23 Source: [54]. 24 25 368. electrothermal atomizer 26 27 28 Atomizer which is heated to the temperature required for analyte atomization by the 29 passage of electrical current through its body. 30 31 Note 1: An electrothermal atomizer typically consists of tube, rod, strip and 32 filament made of refractory material that is heated by a low voltage, high 33 current device, providing a means of obtaining variable temperatures 34 35 according to the nature of the analyte. 36 37 Note 2: Electrothermal atomizers are often made of graphite (polycrystalline 38 electrographite), and glassy carbon, termed ‘graphite furnace’. 39 40 Source: [54]. See also: electrothermal atomic absorption spectroscopy. 41 42 43 369. electrothermal vaporization 44 45 Technique for sample introduction based on the use of a solid furnace heated at a 46 controlled temperature to vaporize the sample prior to its introduction into an 47 inductively-coupled plasma. 48 49 50 Source:[54, 56]. 51 52 370. Esum 53 54 Energy that must be supplied to an atom to transfer it from the ground atomic state to a 55 given ionic excited state. 56 57 58 Source: [10]. 59 60

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1 2 3 371. excitation source 4 5 6 See: atomic excitation source. 7 8 372. flame atomic spectrometer 9 10 Spectrometer to make measurements by flame atomic spectroscopy. 11 12 13 373. flame atomic spectroscopy 14 flame atomic spectrometry 15 16 Measurement method [VIM 2.5] of atomic spectroscopy that uses a flame to excite 17 atoms. 18 For Peer Review Only 19 374. flame background in flame atomic spectroscopy 20 21 22 See: spectral background of an atomizer or excitation source. 23 24 375. flame in flame atomic spectroscopy 25 26 Continuously flowing mixture of hot gases with a stationary position that derives its 27 28 heat content from a strongly exothermic, irreversible chemical reaction between a fuel 29 and an oxidant. 30 31 Note 1: The flame in general consists of a primary-combustion zone, a secondary- 32 combustion zone and an interconal zone. 33 34 35 Table 375.1: Terms relating to flames in flame atomic spectroscopy. Source: [10]. 36 37 Term Definition Note 38 fuel Reducing agent which reacts with 39 oxidant to provide the energy 40 necessary for atomization and 41 42 excitation. 43 laminar flame Flame for which the gas flow rate The cross- 44 is sufficiently low such that the section of the 45 incoming gaseous flow of fuel flame can have 46 and air is laminar, as is the flame. any shape. 47 oxidant Oxidizing agent which reacts 48 49 with the fuel providing the energy 50 necessary for atomization and 51 excitation. 52 oxidizing flame Flame obtained using an excess 53 of oxidant. 54 reducing flame Flame obtained using an excess 55 of fuel. 56 57 separated flame Flame in which the secondary- 58 combustion zone is separated 59 from the primary-combustion 60 zone.

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1 2 3 turbulent flame Flame in which the burnt-gas 4 flows in an irregular pattern 5 6 7 376. flow spoiler 8 9 Component of a flame atomic spectrometer for creating turbulence in the stream of mist 10 in the spray chamber and removing the largest droplets from this mist by deposition. 11 12 Source: [10]. 13 14 15 377. fluence, F, H 16 17 Energy of a beamFor of electromagneticPeer Review radiation delivered Only per unit area. � = 18 ∫� d� = ∫(d� d�)d� where I is intensity and P radiant power. 19 20 21 Note: SI unit: J m–2. Common unit J cm–2. 22 23 Source: [51], [3] p 35. 24 25 378. fraction atomized 26 27 28 See: local fraction atomised. 29 30 379. gate delay in LIBS 31 time delay in LIBS 32 33 34 Time between the application of a laser pulse and the start of detection in laser-induced 35 breakdown spectroscopy. 36 37 Note 1: The gate delay varies from some hundreds of nanoseconds to several 38 microseconds. 39 40 Note 2: Use of a suitable gate delay allows the high intensity background continuum 41 42 emission present in the early stages of plasma formation to be removed. 43 44 Source: [51]. 45 46 380. GD-OES spectrometers with simultaneous detection 47 48 49 Simultaneous spectrometers for glow discharge optical emission spectroscopy mostly 50 use the so called Paschen–Runge mounting, where the entrance slit, the curved grating 51 and different detectors are aligned along the Rowland circle. Alternatively, Echelle 52 spectrometers are used, which use an Echelle grating in combination with a prism for 53 wavelength separation. Both optical arrangements allow simultaneous monitoring of 54 selected spectral ranges or the whole emission spectra. 55 56 57 Source: [50]. 58 59 60

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1 2 3 381. generator coupling efficiency in ICP spectrometry 4 5 6 Fraction of the energy generated being used for creating and maintaining the plasma in 7 an inductively-coupled plasma spectrometer. 8 9 Source: [52]. 10 11 382. glow discharge source 12 13 14 Component of an atomic emission spectrometer employing a glow electric discharge 15 used in atomic emission spectroscopy for qualitative and quantitative analysis of solid 16 materials. 17 For Peer Review Only 18 Note: Glow discharge allows volatilization as well as excitation of analytes and 19 sample matrices. 20 21 22 Source: [50]. 23 24 383. glow electric discharge 25 glow discharge 26 27 Electric discharge in gas at low pressure (100 – 1000 Pa). 28 29 30 Note 1: In atomic emission spectroscopy argon is used as the inert working gas 31 which generates the plasma. 32 33 Note 2: In the prevailing electrical field the produced ions are accelerated towards 34 the cathode, resulting in a continuous bombardment of the sample surface. 35 36 37 Source: [50]. 38 39 384. glow-discharge optical emission spectroscopy, (GD-OES) 40 41 Optical emission spectroscopy in which a glow electric discharge excites atoms at the 42 surface of a sample which is made the cathode of the discharge. 43 44 45 385. Grimm-type cathode 46 47 Cathode consisting of a flat sample which is cooled during the discharge process so that 48 thermal volatilization is suppressed, and the sample material is removed by sputtering 49 only. 50 51 52 Source: [50]. 53 54 386. hollow-cathode discharge source 55 56 Glow discharge source with a graphite cathode, into which the sample is inserted in the 57 form of drillings, a pressed pellet or a dry solution residue. 58 59 60 Note: For this source, sample volatilization takes place mainly by thermal effects.

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1 2 3 Source: [50]. 4 5 6 387. hollow-cathode lamp 7 line source 8 9 Glow discharge source of spectral lines of an atom in which the cathode is made of the 10 desired element. 11 12 13 Note: It is often referred to as line source, as opposed to a continuum source. 14 15 Source:[56]. 16 17 388. incident power 18 For Peer Review Only 19 Power supplied by a generator to the plasma. 20 21 22 Source: [57]. 23 24 389. inductively-coupled plasma, (ICP) 25 26 Plasma produced by induction by means of a high-frequency (about 2 500 Hz) 27 28 electromagnetic field. The region of gas at high temperature and free from the field is 29 taken as the region of observation. 30 31 Source: [52]. See also: inductively-coupled plasma optical emission spectroscopy, 32 inductively-coupled plasma mass spectrometry. 33 34 35 390. inductively-coupled plasma (ICP) spectrometry 36 inductively-coupled plasma spectroscopy 37 38 Measurement method [VIM 2.5] of atomic spectroscopy that uses an inductively- 39 coupled plasma to excite and ionize atoms. 40 41 Note: ICP methods are described by their method of detection of ions in the 42 43 plasma and include inductively-coupled plasma optical emission 44 spectroscopy, and inductively-coupled plasma mass spectrometry. 45 46 391. inductively-coupled plasma mass spectrometry, (ICP-MS) 47 48 Measurement method [VIM 2.5] of atomic spectroscopy that uses an inductively- 49 50 coupled plasma to excite and ionize atoms with measurement of the number and kind 51 of ions in the plasma using mass spectrometry. 52 53 392. inductively-coupled plasma optical emission spectroscopy, (ICP-OES) 54 55 Measurement method [VIM 2.5] of atomic spectroscopy that uses an inductively- 56 coupled plasma to excite and ionize atoms with measurement of the number and kind 57 58 of ions in the plasma from their emission of electromagnetic radiation (see optical 59 emission spectroscopy). 60

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1 2 3 393. inductively-coupled plasma robustness 4 plasma robustness 5 6 7 Ability of an inductively-coupled plasma to withstand slight modification in the 8 operating conditions and/or matrix composition with no significant changes in its 9 fundamental characteristics (i.e., temperatures, electron number density) or the 10 analytical figures of merit (i.e., sensitivity, detection limits or signal-to-noise ratio) 11 12 13 Source: [52]. 14 15 394. inductively-coupled plasma thermal pinch 16 17 Decrease in theFor inductively-coupled Peer Review plasma volume normallyOnly caused when an organic 18 volatile solution is delivered to it. Organic vapours diffuse towards the outermost area 19 of the plasma and its volume decreases. 20 21 22 Source: [52]. 23 24 395. inductively-coupled plasma torch 25 26 Quartz component of an inductively coupled plasma spectrometer where the plasma is 27 28 generated and stabilized. 29 30 Note: In ICP the torch is an open three concentric tubes assembly allowing the 31 introduction of the three gas streams constituting the plasma. The inner tube 32 of the torch can be made of a different material such as alumina and is 33 usually called the injector. 34 35 36 Source: [52]. 37 38 396. initial plasma radiation zone in ICP-OES 39 40 Inductively-coupled plasma volume in inductively-coupled plasma optical emission 41 spectroscopy where the analytically relevant light emission begins to be observed. 42 43 44 Source: [52]. 45 46 397. injector in an ICP torch 47 48 See: inductively-coupled plasma torch. 49 50 51 398. interference curve in atomic spectroscopy 52 53 Graph of absorbance or intensity plotted as a function of the concentration of an 54 interfering element. 55 56 399. inverse Bremsstrahlung 57 58 59 Absorption of photon energy by free electrons. 60

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1 2 3 Note: Inverse Bremsstrahlung increases the kinetic energy of the electrons which 4 is important for heating the plasma. 5 6 7 Source: [51]. See also: Bremsstrahlung emission, Bremsstrahlung radiation. 8 9 400. ionic cloud in atomic spectroscopy 10 11 Gas phase containing free ions of analyte. 12 13 14 Source: [10]. 15 16 401. ionization buffer 17 For Peer Review Only 18 Buffer which decreases and stabilizes the ionization of free atoms of analyte by 19 increasing the concentration of free electrons in the atomizer. 20 21 22 Source: [10]. 23 24 402. ionization energy 25 26 Minimum energy that must be supplied to remove an electron from an atom in the 27 28 ground state. 29 30 Source: [10]. 31 32 403. laser ablation 33 34 35 Removal of material as an aerosol from a surface on irradiation by a laser beam. 36 37 Source: [51]. 38 39 404. laser induced breakdown spectroscopy, (LIBS) 40 41 Measurement method [VIM 2.5] of atomic spectroscopy that uses a focused laser beam 42 43 to ablate, atomize and excite atoms from a sample surface with subsequent 44 measurement of the generated electromagnetic radiation. 45 46 Source: [51]. 47 48 405. laser-induced breakdown spectrum 49 50 51 Emission spectrum generated as a consequence of the decay of the excited states 52 generated in a laser-induced plasma that consists of a continuous background and 53 element-specific atomic or ionic lines and molecular bands. 54 55 Note: LIBS spectra cover a wide wavelength range: commonly LIBS 56 57 measurements are taken between the wavelengths of 200 nm and 1000 nm. 58 59 Source: [51]. 60

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1 2 3 406. laser-induced plasma 4 5 6 Local plasma formed by the interaction between a laser beam and a solid sample and 7 initiated by the production of primary electrons by multiphoton ionization and 8 thermionic photoemission mechanisms. 9 10 Note: As well as electrons, laser-induced plasma contains ions, and neutral atoms 11 as well as excited species of the ablated matter. Decay of these excited 12 13 species generates the light emission analysed in laser-induced breakdown 14 spectroscopy. 15 16 Source: [51]. 17 For Peer Review Only 18 407. line 19 20 21 See: spectral line of an atom. 22 23 408. line-broadening in atomic spectroscopy 24 25 Increase in the theoretical width of a spectral line owing to thermal motion of emitting 26 atoms (Doppler effect), to electric field (Stark effect), to self-absorption and to pressure 27 28 (Lorentz effect). 29 30 Note: Line-broadening increases the measurement uncertainty [VIM 2.26] of a 31 measurement. 32 33 Source: [10]. 34 35 36 409. line profile 37 38 Graph of the variation of emitted radiation intensity as a function of wavelength 39 (emission line) or the variation of the absorption factor as a function of wavelength 40 (absorption line). 41 42 43 Source: [10]. 44 45 410. line source 46 47 See: hollow-cathode lamp. 48 49 50 411. local fraction atomized 51 fraction atomised 52 53 Number of free atoms divided by the total number of atoms of the analyte present in the 54 gaseous phase in the observation volume in atomic spectroscopy, the latter being the 55 volume confined by the atomizer or immediately adjacent to it. 56 57 58 Source: [10]. 59 60

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1 2 3 412. low sample consumption system in ICP spectrometry 4 5 6 Liquid-sample introduction system to an inductively-coupled plasma spectrometer 7 adapted to work at sample flow rates below 100 µL min-1. 8 9 Note: The system is normally composed of a micro-nebulizer and a low inner 10 volume spray chamber. 11 12 13 Source: [52]. 14 15 413. L’vov platform 16 17 See: platform atomization in ETAAS. 18 For Peer Review Only 19 20 414. measurement efficiency in ICP spectrometry 21 22 Number of detector events per atom in the sample. 23 24 Source: [52]. 25 26 27 415. microwave cavity 28 29 Resonant cavity that permits focusing a microwave field inside a discharge tube thus 30 giving rise to a standing wave. 31 32 Source: [52]. 33 34 35 416. microwave-induced plasma 36 microwave plasma 37 38 Plasma generated in a microwave cavity. 39 40 Note: The plasma results as a consequence of ionization of a given gas in 41 42 presence of electrons and a microwave field. 43 44 Source: [52]. 45 46 417. multiphoton ionization 47 48 49 Absorption of multiple photons by an atom such that the accumulated energy of the 50 absorbed photons is greater than the ionization potential of the atom. 51 52 Source: [51]. 53 54 418. nebulization 55 56 57 Conversion of a liquid into an aerosol consisting of droplets suspended in a gas stream. 58 59 Source: [10]. 60

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1 2 3 419. nebulizer 4 5 6 Device for producing nebulization. 7 8 Source: [10]. 9 10 420. non-specific emission or attenuation 11 12 13 Electromagnetic radiation, within the bandpass filter used, emitted by, or absorption 14 caused by, atoms, molecules and radicals that are subject to the atomizer by all 15 components, apart from the analyte, that are present there during measurement. 16 17 Note: These effects include scattering or absorption effects by solid particles. 18 For Peer Review Only 19 Source: [10]. 20 21 22 421. normal plasma analytical zone in ICP-OES 23 24 Inductively-coupled plasma volume mainly responsible for emission of analytically- 25 useful light because processes leading to excited species, such as droplet desolvation, 26 element vaporization, atomization (or ionization) and excitation have been completed. 27 28 29 Source: [52]. 30 31 422. observation height 32 33 Vertical distance between the optical axis of observation in a flame atomic 34 35 spectrometer and the horizontal plane of the top of the burner. 36 37 Source: [10]. 38 39 423. optical emission spectroscopy, (OES) 40 41 Measurement principle [VIM 2.4] of atomic emission spectroscopy in which the 42 43 emitted electromagnetic radiation is in the range of frequencies from the infrared, 44 through visible, to the ultra-violet region. 45 46 Note: OES is used as the detector in inductively-coupled plasma optical emission 47 spectroscopy, and glow-discharge optical emission spectroscopy. 48 49 50 424. overall efficiency of atomization 51 52 In atomic spectroscopy, mass of analyte converted into free atoms in the atomizer 53 divided by mass of analyte entering the dispersion device. 54 55 Source: [10]. 56 57 58 425. Paschen-Runge mounting 59 60 See: GD-OES spectrometers with simultaneous detection.

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1 2 3 426. Penning excitation/ionization in ICP spectrometry 4 5 6 Collisional excitation and ionization mechanism of inductively-coupled plasma 7 spectrometry involving analyte atoms and metastable argon atoms. 8 9 Source: [52]. 10 11 427. percentage transmission of sample 12 13 14 In atomic spectroscopy, flux of mass of sample divided by the flux of mass of solvent 15 blank, measured under the same conditions, expressed as a percentage. 16 17 Source: [10]. 18 For Peer Review Only 19 428. permanent modifier in ETAAS 20 21 22 Substance added together with the sample or standards in electrothermal atomic 23 absorption spectroscopy that is refractory, or forms a refractory species (e.g., a 24 carbide), and thus does not need to be renewed for several atomization cycles. 25 26 Note: This is a particular type of chemical modifier for electrothermal AAS. 27 28 29 Source:[58]. 30 31 429. plasma 32 33 Matter brought into the gaseous state, largely ionized, and emitting and absorbing 34 35 electromagnetic radiation. 36 37 Note 1: In practice, the term ‘plasma’ is restricted to cases where the temperature is 38 greater than 7 000 K. 39 40 Note 2: A plasma may be generated by an electric discharge. 41 42 43 Source: [57]. 44 45 430. plasma arc 46 47 Plasma formed by an arc-discharge. 48 49 50 Note: The discharge is blown through a suitable orifice to form a plasma jet. The 51 high-temperature, electric field-free gaseous region is designed as the 52 region of observation. 53 54 Source: [10]. 55 56 57 431. plasma excitation temperature 58 59 Temperature governing the number density of atomic species in their ground state and 60 excited states following a Boltzmann distribution.

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1 2 3 Source: [57]. 4 5 6 432. plasma gases in ICP 7 8 Gas streams used to maintain and stabilize the inductively-coupled plasma. The 9 external stream is the main constituent of the plasma and confines the plasma avoiding 10 melting of the torch walls; the intermediate gas stream keeps the plasma at a given 11 height above the top of the torch and, the central stream carries the aerosol and 12 13 promotes its injection in the plasma central channel. 14 15 Source: [52]. 16 17 433. plasma induction zone 18 For Peer Review Only 19 Inductively-coupled plasma volume where there is a maximum interaction between the 20 21 electromagnetic field and the plasma gas (mostly argon). This is the plasma hottest area 22 and has a toroidal configuration. 23 24 Source: [52]. 25 26 434. plasma ionization temperature 27 28 29 Temperature associated with the energy level of plasma ions. 30 31 Source: [57]. 32 33 435. plasma local thermodynamic equilibrium, (LTE) 34 35 36 Condition for which the temperatures estimated from different particles (atoms, 37 molecules, ions, electrons) constituting a plasma are locally coincident. 38 39 Source: [57]. 40 41 436. plasma robustness 42 43 44 See: inductively-coupled plasma robustness. 45 46 437. plasma shielding in LIBS 47 48 Prevention of laser pulse energy from reaching a sample surface as a result of the 49 50 presence of a laser-induced plasma. 51 52 Note: The main process leading to plasma shielding is the absorption of the laser 53 energy by electrons (inverse Bremsstrahlung) and multiphoton ionization 54 (mainly relevant for shorter laser wavelengths). 55 56 Source: [51]. 57 58 59 60

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1 2 3 438. plasma termination in LIBS 4 5 6 Extinction of the plasma after a laser pulse as a consequence of self-absorption 7 (quenching) and recombination of electrons and ions. 8 9 Note: The time elapsed between initiation and extinction of the plasma ranges 10 from tenths of microseconds to a few milliseconds. 11 12 13 Source:[51]. 14 15 439. platform atomization in ETAAS 16 L’vov platform, 17 For Peer Review Only 18 Sample support made of graphite that is inserted into the atomizer tube in 19 electrothermal atomic absorption spectroscopy. The sample, a liquid or a solid, is 20 21 deposited onto this platform, from which it undergoes all the transformations leading to 22 atomization. The use of a platform delays atomization, until a more stabilized 23 temperature in the gas phase is reached. 24 25 Source: [54]. 26 27 28 440. pneumatic nebulizers 29 30 Nebulizers for which the aerosol generation principle is based on the exposure of the 31 liquid sample to a high velocity gas stream. 32 33 Note: Most common designs include cross flow, concentric, parallel path, 34 entrained and Babington and V Groove. 35 36 37 Source: [52]. 38 39 441. preheating inductively-coupled plasma zone 40 preheating plasma zone 41 42 43 Inductively-coupled plasma volume where tertiary aerosols suffer from complete 44 solvent evaporation, element salt vaporization and dissociation into atoms. 45 46 Source: [52]. 47 48 442. premix burner 49 50 51 Burner in a flame atomic spectrometer in which the fuel, the oxidant and the aerosol 52 are mixed before reaching the flame. (See: flame in flame atomic spectroscopy). 53 54 Note: A premix burner generally produces a laminar flame (See: flame in flame 55 atomic spectroscopy). 56 57 58 Source: [10]. 59 60

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1 2 3 443. primary aerosol 4 5 6 Aerosol generated by a nebulizer. 7 8 Note: Usually, primary aerosols contain coarse droplets, they are polydisperse in 9 terms of drop diameters and they are turbulent. 10 11 Source: [52]. 12 13 14 444. pulse duration of a laser 15 pulse width 16 pulse length 17 For Peer Review Only 18 Time duration of laser pulses. 19 20 21 Note: Pulse duration depends on the laser system used and can vary between 22 hundreds of femtoseconds to a few nanoseconds. 23 24 Source: [51]. 25 26 445. pulse energy of a laser 27 28 29 Total optical energy content of a laser pulse – the integral of optical power over pulse 30 duration. 31 32 Note: Pulse energies range from microjoules to millijoules for Q-switched lasers, 33 whereas mode-locked lasers achieve much lower pulse energies (picojoules, 34 nanojoules or sometimes several microjoules). 35 36 37 Source: [51]. 38 39 446. pulse frequency 40 41 See: repetition rate of a pulsed laser. 42 43 44 447. pulsed laser 45 46 Laser system which emits electromagnetic radiation in the form of pulses of a defined 47 and constant duration. 48 49 Note: A pulsed laser produces no continuous optical wave. 50 51 52 Source:[51]. 53 54 448. pyrolysis curve in ETAAS 55 56 Graph of absorption against pyrolysis temperature in electrothermal atomic absorption 57 spectroscopy. 58 59 60 Source: [54].

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1 2 3 449. quartz atomizer 4 5 6 Atomizer that is used to atomize those elements that form volatile species (e.g., 7 hydrides) at relatively low temperatures (e.g. 1000 ºC or below). 8 9 Note: These can be heated externally or positioned in a flame (See: flame in flame 10 atomic spectroscopy). 11 12 13 Source:[56]. 14 15 450. radial viewing mode 16 17 Inductively coupledFor plasma Peer optical Review emission spectrometer Only configuration in which the 18 plasma and the entrance slit are perpendicular and from which the signal is taken 19 perpendicularly to the main plasma axis. 20 21 22 Note: This configuration is less sensitive than axial viewing mode. 23 24 Source: [52]. 25 26 451. radiofrequency (RF) generator in an ICP spectrometer 27 28 29 Component of an inductively-coupled plasma spectrometer responsible for the 30 generation of alternating current in the radiofrequency portion of the electromagnetic 31 spectrum. 32 33 Source: [52]. 34 35 36 452. radiofrequency glow discharge optical emission spectroscopy, (RF-GD- 37 OES) 38 39 Optical emission spectroscopy in which a radiofrequency-powered glow discharge is 40 operated with frequencies in the low megahertz range. 41 42 43 Note: The use of these frequencies establishes a negative direct current (DC)-bias 44 voltage on the sample surface. The DC-bias is the result of an alternating 45 current waveform that is centered about negative potential; as such it more 46 or less represents the average potential residing on the sample surface. 47 Radio-frequency has ability to appear to flow through insulators (non- 48 conductive materials). 49 50 51 Source: [50]. 52 53 453. reference flux density, ϕr(λ) 54 55 Intensity transmitted by the reference medium in a double-beam spectrometer. 56 57 58 Source: [10]. See also: sample flux density. 59 60

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1 2 3 454. reflected power 4 5 6 Incident power that is not absorbed by the plasma. 7 8 Source: [57]. 9 10 455. repetition rate of a pulsed laser 11 pulse frequency 12 13 14 Number of laser pulses emitted by a pulsed laser system per unit time. 15 16 Note 1: For laser systems with pulse duration in the nanosecond regime repetition 17 ratesFor range Peer from 1 to 20Review Hz, whereas for Onlyfemtosecond laser systems 18 increased repetition rates up to 1000 Hz are possible. 19 20 21 Note 2: SI unit: Hz. 22 23 Source: [51]. 24 25 456. residence time in ETAAS 26 27 28 Time in which the analyte is confined within the observation volume in electrothermal 29 atomic absorption spectroscopy. 30 31 Source: [54]. 32 33 457. resonant inelastic X-ray scattering, (RIXS) 34 35 resonant X-ray emission 36 resonant X-ray Raman 37 38 Measurement method [VIM 2.5] of inelastic X-ray spectroscopy that uses a hard or soft 39 X-ray beam to excite transitions of core-level electrons into empty energy levels. The 40 subsequent transition of an electron into the core state is accompanied by X-ray 41 emission with characteristic momentum and energy. 42 43 44 Note: The incident photon energy is selected for resonance with an X-ray 45 absorption edge of the system, such that the observed shifts in momentum 46 and energy provide element-specific chemical sensitivity, with the capacity 47 to distinguish the same element located at inequivalent sites 48 49 50 Source: [59]. 51 52 458. Rowland circle 53 54 See: GD-OES spectrometers with simultaneous detection. 55 56 459. Saha’s ionization equation 57 58 Saha–Langmuir equation 59 60

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1 2 3 Equation that relates the ionization state of an element present in a gas in thermal 4 equilibrium to the temperature and the pressure of the medium. 5 6 7 Note 1: For a gas composed of a single atomic species, the Saha equation is written: 8 9 � ―3 � ( � + 1 ��)�e = 2� ( � + 1 ��)exp[ ― (�� + 1 ― ��) ��] 10 11 12 where �� is the number density of atoms with i electrons removed, gi is the 13 degeneracy of the ith state, �� is the ionization energy of the ith state, ne is 14 the number density of electrons, � is the thermal de Broglie wavelength of 15 16 an electron, k is the Boltzmann constant, and T is the thermodynamic 17 temperature of the gas. 18 For Peer Review Only 19 Note 2: The thermal de Broglie wavelength is given by: 20 21 ℎ2 22 � = 23 2� �e � � 24 25 26 where h is the Planck constant, k the Boltzmann constant, T temperature, and me the 27 mass of an electron. 28 29 Source: [57]. 30 31 460. sample flux density, ϕs(λ) 32 33 34 Intensity transmitted by the atomizer when the latter is supplied with the sample 35 solution or a reference solution. 36 37 Source: [10]. See also: reference flux density. 38 39 461. saturator 40 41 42 Buffer containing interfering element(s) in sufficient quantity to reach the limit of 43 enhancement or dispersion (i.e. saturation) of the interference curve. 44 45 Source: [10]. 46 47 462. self-absorption 48 49 50 Partial absorption of electromagnetic radiation emitted by excited atoms in an atomic 51 emission source by atoms of the same kind present in the source. 52 53 Note 1: As a result of self-absorption, the observed intensity of a spectral line may 54 be less, and its width greater, than would be the case for a source having a 55 56 very small optical path and the same concentration of emitting atoms per 57 unit volume. 58 59 Note 2: Self-absorption may occur in all emitting sources, whether they are 60 homogeneous or not, thermal or non-thermal.

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1 2 3 Source: [10]. 4 5 6 463. self-reversal in atomic emission 7 8 Absorption of electromagnetic radiation emitted from the centre of an ionic cloud by 9 outer layers of the emitting vapour, which are cooler than the centre. 10 11 Note 1: The intensity measured at the centre of a line is less than the intensity 12 13 measured on either side of the centre. 14 15 Note 2: In extreme cases, the intensity at the centre of the line is so weak that only 16 the wings remain, giving the appearance of two fuzzy lines. 17 For Peer Review Only 18 Source: [10]. 19 20 21 464. sequential detection in glow discharge optical emission spectrometry 22 23 Sequential spectrometers use a dispersive element (grating) in combination with 24 entrance and exit slits for selection of specific wavelengths. Geometric arrangements 25 include the Czerny-Turner and the Ebert-geometry, both offering high resolution 26 measurements. However, they do not permit simultaneous recording of different 27 28 spectral lines, even for ingle emission line intensity, and adjacent spectral background 29 has also to be measured sequentially. 30 31 Source: [50]. 32 33 465. solvent blank flux density, ϕ (λ) 34 T 35 36 Intensity transmitted by the atomizer when the latter is supplied with the solvent blank. 37 38 Source: [10]. 39 40 466. solvent nucleation 41 42 43 Solvent condensation on solid particles or droplets contained in an aerosol. 44 45 Source: [52]. 46 47 467. solvent transport rate in an ICP spectrometer 48 49 50 Mass of solvent, both in liquid and vapour forms, reaching an inductively-coupled 51 plasma per unit of time. 52 53 Source: [52]. 54 55 468. spectral background of an atomizer or excitation source 56 57 58 Electromagnetic radiation, within the bandpass used, emitted by, and/or in the case of 59 atomic absorption spectroscopy, absorbed in, the atomizer when nothing is supplied to 60 the atomizer but the gases involved in its operation.

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1 2 3 Note: In the case of flame atomic spectroscopy, the term "flame background" is 4 used. 5 6 7 Source: [10]. 8 9 469. spectral line of an atom 10 spectral line 11 line 12 13 14 In atomic spectroscopy, a very narrow band of frequencies of electromagnetic radiation 15 emitted or absorbed by atoms which undergo a single electronic transition. 16 17 Note 1: TheFor radiation Peer is centred Review on a peak whose Onlywavelength characterizes the line 18 and which corresponds to the emission or absorption maximum. 19 20 21 Note 2: A distinction is made between lines corresponding to transition of neutral 22 atoms (e.g. Ba I 553.548 and 577.762 nm) and ions (e.g. Ba II 455.403 nm). 23 24 Source: [10]. 25 26 470. spray chamber 27 28 29 Chamber of a nebulizer in which the sprayed liquid is converted to mist. Some of the 30 droplets of this mist may evaporate, coalesce, or deposit in the chamber and 31 subsequently drain away as waste. 32 33 Source: [10]. 34 35 36 471. sputter rate 37 38 Mass of material removed from a sample surface in unit time 39 40 Note: Usually the sputter rate is given in µg s−1. 41 42 43 Source: [50]. 44 45 472. stop-flow conditions in ETAAS 46 47 Stoppage to the otherwise constant flow of argon gas to the atomizer in electrothermal 48 atomic absorption spectroscopy, that can be programmed to occur during atomization, 49 50 for the purpose of increasing the residence time of the analyte atoms and thus the 51 associated signal. 52 53 Source: [54]. 54 55 473. synchrotron X-ray spectroscopy 56 57 58 X-ray spectroscopy performed using a high intensity, continuous polychromatic 59 synchrotron X-ray source 60

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1 2 3 Source: [60]. 4 5 6 474. tertiary aerosol in an ICP spectrometer 7 8 Aerosol that reaches an inductively-coupled plasma. 9 10 Note: Such aerosols are finer than primary aerosols, less polydispersed and less 11 turbulent than primary aerosols. 12 13 14 Source: [52]. 15 16 475. thermal dispersion 17 For Peer Review Only 18 Procedures whereby an aerosol is produced at a high temperature, for example by 19 sparks, arcs, furnaces, lasers, cathodic sputtering or electron-beam. 20 21 22 Source: [10]. 23 24 476. thermal volatilization 25 26 Process in glow-discharge atomic emission spectroscopy in which sample volatilisation 27 28 occurs by heating due to sample bombardment with argon ions. 29 30 Note 1: The process causes evaporation of the sample constituents in accordance to 31 their boiling-points. 32 33 Note 2: Although this technique offers highest detection power for most volatile 34 35 elements its use in routine applications is still limited by the analytical 36 challenges posed by the transient nature of the analyte signal. 37 38 Source: [50]. 39 40 477. time delay in LIBS 41 42 43 See: gate delay in LIBS. 44 45 478. time-resolved laser-induced breakdown spectroscopy 46 47 Measurement method [VIM 2.5] of laser-induced breakdown spectroscopy in which the 48 emitted radiation is monitored with time resolution sufficiently high to resolve different 49 50 stages in the lifetime of the laser-induced plasma. 51 52 Source: [51]. 53 54 479. total sample consumption system 55 56 Liquid-sample introduction system able to achieve 100% transport efficiency. 57 58 59 Source: [52]. 60

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1 2 3 480. transport efficiency of a sample 4 5 6 Mass of analyte entering the atomizer of a flame atomic spectrometer divided by the 7 mass of analyte entering the dispersion device. 8 9 Source: [10]. 10 11 481. ultrasonic nebulizers 12 13 14 Nebulizers whose aerosol generation principle is based on the transfer of the energy 15 from a vibrating transducer to the liquid sample. 16 17 Source: [52]. 18 For Peer Review Only 19 482. volatilization 20 21 22 Conversion of the solute particles containing the analyte from the solid and/or liquid 23 phase to the vapour phase. 24 25 Source: [10]. 26 27 28 483. wall atomization in ETAAS 29 30 Electrothermal atomic absorption spectroscopy in which the sample is deposited 31 directly onto the wall of the electrothermal atomizer tube, from which it undergoes all 32 the transformations leading to atomization. 33 34 35 Source: [54]. 36 37 484. wash out time 38 39 Time required for the output signal of an inductively-coupled plasma spectrometer for a 40 given analyte to fall back to baseline levels from the end of sampling time and/or after 41 introducing a blank solution. 42 43 44 Source: [52]. 45 46 485. X-ray emission spectrum 47 48 Spectrum comprising the continuum Bremsstrahlung and the most energetic 49 50 characteristic spectral lines defined by differences in binding energy between electron 51 energy levels. 52 53 Source: [60]. 54 55 486. X-ray excited Auger electron spectroscopy, (XAES) 56 57 58 Auger spectroscopy that uses a synchrotron X-ray beam for excitation of the sample. 59 60 Source: [55].

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1 2 3 487. X-ray photoelectron 4 5 6 Electron emitted from an atom following the absorption of an X-ray photon. 7 8 Source: [55]. 9 10 488. X-ray photoelectron spectroscopy, (XPS) 11 electron spectroscopy for chemical analysis, (ESCA) 12 13 14 Measurement method [VIM 2.5] of electron emission spectroscopy that uses an X-ray 15 source to stimulate the emission of photoelectrons from a surface. These photoelectrons 16 have energies characteristic of transitions specific to the chemical elements from which 17 they were emitted. 18 For Peer Review Only 19 Note 1: Laboratory XPS systems usually operate under high or ultra-high vacuum. 20 21 22 Note 2: Synchrotron X-ray XPS can be performed under vacuum, ambient, or high 23 pressure, enabling investigations of surfaces under ambient and extreme 24 conditions. 25 26 Source: [14]. 27 28 29 489. X-ray spectroscopy 30 31 Measurement of X-rays emitted by a solid that has been bombarded with electrons. 32 Spectrum consists of a continuous (Bremsstrahlung) and discrete (characteristic) parts 33 34 35 Source: [60]. 36 37 MOLECULAR SPECTROSCOPY 38 39 This section on molecular spectroscopy covers infrared (IR) and Raman spectroscopy 40 which are complementary vibrational spectroscopy techniques. Both have an extensive 41 range of molecular structure, environmental, identification and quantitative analysis of 42 43 material applications (both bulk and surface), which, inter alia, include academic and 44 industrial research, product quality assurance and process control, remote-sensing, 45 forensics (crime scene, art and archaeology), agricultural product quality assessment, 46 clinical and bio-medical research and diagnoses. Today, a wide range of instruments to 47 suit a wide range of applications and to suit specific purposes are available from 48 laboratory-based research tools to industrial process-analysers to hand-held 49 spectrometers, to at point-of-care medical devices. 50 51 52 Infrared spectroscopy involves the absorption (or interaction) of infrared radiation with 53 matter. The IR region of the electromagnetic spectrum is typically divided into three 54 sub regions, the near-IR (NIR) region extends from wavenumbers about 12 800 cm–1 to 55 4000 cm–1 (wavelengths 780 nm to 2.5 µm), the mid-IR region from 4000 cm–1 to 400 56 –1 –1 –1 57 cm (2.5 µm to 25 µm), and the far-IR region from 400 cm to about 10 cm (25 µm 58 to approximately1000 µm). A mid-IR spectrum is that typically used for 59 “fingerprinting” a material and can also be utilised for physical form and/or chemical 60 group identification. The astronomer Sir William Herschel discovered the first non-

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1 2 3 visible (near-infrared, NIR) region of the electromagnetic spectrum in 1800. Early 4 developments in observations and instrumentation for both NIR and mid-IR came to the 5 6 fore in the early 1900s, with major studies on molecular group-characteristic structures 7 using mid-IR spectroscopy being continually developed in the 1900s. 8 9 The observation of inelastic scattering of photons of light was demonstrated and 10 reported in 1928 by Sir C.V. Raman and K.S. Krishan. Like infrared spectroscopy, it 11 can be used to study the vibrational, rotational and low-frequency modes of vibration of 12 a substance. Today, the inelastic scattering of light by monochromatic radiation (a 13 14 laser) is known as Raman scattering, with the shift in energy of the observed photons 15 yielding similar but complementary information to that observed within an infrared 16 spectrum. 17 For Peer Review Only 18 For a molecular vibration to be infrared active, i.e. produce an absorption band, then the 19 vibration must be accompanied by a change in dipole moment; for a molecular 20 21 vibration to be Raman-active, then during the vibration there must be a change in 22 polarizability. 23 24 25 490. amorphous material transmitting infrared radiation, (AMTIR) 26 27 Amorphous glasses made from elements of groups 4, 5 and 6 of the Periodic Table that 28 transmit infrared radiation. 29 30 31 Note: AMTIRs are hard but can be brittle. 32 33 Examples: AMTIR-1 which is Ge33As12Se55 and AMTIR-3 which is Ge28Sb12Se60. 34 35 Source: [6]. 36 37 38 491. amplitude modulation 39 40 Modulation of the amplitude of a beam of electromagnetic radiation; by the movement 41 of a moving mirror in a rapid scan Fourier-transform spectrometer or by a mechanical 42 chopper in other spectrometers. 43 44 45 Source: [6]. 46 47 492. anharmonicity 48 49 See: electrical anharmonicity, mechanical anharmonicity. 50 51 52 493. anisotropic Raman scattering 53 54 Raman scattering by the anisotropic part of the derived polarizability tensor. 55 56 Source: [6]. 57 58 59 60

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1 2 3 494. anomalous dispersion of the refractive index 4 5 6 Changes in real refractive index of a material in the vicinity of an absorption band in 7 which real refractive index decreases markedly with decreasing wavenumber on the 8 high wavenumber side of an absorption band, then increases rapidly through the band 9 centre and decreases markedly on the low wavenumber side of the band, before 10 resuming normal dispersion at wavenumbers far from the band. 11 12 13 Source: [6]. 14 15 495. anomalously polarized Raman band 16 17 Raman bandFor with a depolarization Peer Review ratio greater than 0.75,Only as is frequently observed in 18 surface-enhanced resonance Raman spectroscopy. 19 20 21 Source: [6]. 22 23 496. anti-Stokes Raman scattering 24 25 Raman scattering of electromagnetic radiation in which the scattered radiation has 26 greater energy (greater wavenumber) than the exciting radiation. 27 28 29 Source: [6]. See also: Stokes Raman scattering. 30 31 497. asymmetric top 32 33 Rotor whose three principal moments of inertia are all different. 34 35 36 Source: [6]. 37 38 498. atomic polar tensor, (APT) 39 40 3x3 tensor that gives the change in the components of the molecular dipole moment 41 when the atom is displaced in three-dimensional space. 42 43 44 Note 1: The rows correspond to different components of the dipole moment and the 45 columns to x, y and z displacements. 46 47 Note 2: APTs have been widely used in the analysis of infrared absorption 48 intensities. 49 50 –1 –20 51 Note 3: SI unit: C. Common units: D Å ≈ 3.335 64 × 10 C. 52 53 Source: [6]. 54 55 499. attenuated total reflection spectroscopy 56 57 internal reflection spectroscopy, (IRS) 58 frustrated total internal reflection spectroscopy 59 60

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1 2 3 Measurement method [VIM 2.5] of molecular spectroscopy based on internal reflection 4 from an absorbing material at angles of incidence at or above the critical angle 5 6 (attenuated total reflection). 7 8 Note: Attenuated total reflection occurs where the material absorbs. The resulting 9 spectrum resembles an absorption spectrum of the sample. 10 11 Source: [6]. 12 13 14 500. band shape 15 16 Description of the profile of a spectral band. 17 For Peer Review Only 18 Note: For a given band, the band shape is independent of the band height in 19 Raman spectra, infrared absorption spectra and pATR spectra. The band 20 21 shape changes if the band height changes in infrared transmission spectra or 22 attenuated total reflection spectra. 23 24 Source: [6]. 25 26 501. Bragg filter 27 28 29 Optical filter used, for example, to attenuate Rayleigh scattering while transmitting 30 light subject to Raman shift. 31 32 Note: Historically, a Bragg filter was a colloidal dispersion of spheres in a regular 33 close packed array, which selectively diffracts/ reflects wavelengths that 34 satisfy the Bragg diffraction criterion for the lattice but transmits all other 35 36 wavelengths. Now largely superseded by Volume Bragg Gratings, where 37 photo-induced modulation of the refractive index of the filter medium is 38 used to form a volume phase hologram with reflecting planes separated by a 39 well-defined spacing. In each case, angle tuning is used to match the laser 40 wavelength to the Bragg diffraction condition. The filter can be 41 manufactured either as a notch filter, which transmits wavelengths either 42 43 side of the laser line, or as an edge filter, which only transmits wavelengths 44 longer than the laser line (i.e. Raman light subject to Stokes scattering). 45 46 Source: [6]. 47 48 502. centre burst 49 center burst 50 51 52 Spectral region of an interferogram around zero-path-difference where intensity is 53 greatest. 54 55 Source: [6]. 56 57 58 503. channel fringes 59 See: interference fringes. 60

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1 2 3 504. Christiansen effect 4 5 6 Collections of solid particles that are transparent to radiation of a particular wavelength 7 and are slightly larger than the wavelength of the radiation transmit poorly due to 8 reflection and scattering from the interfaces. The transmission increases markedly at 9 wavenumbers at which the refractive index of the particles is close to that of the 10 surrounding medium. 11 12 13 Note: The Christiansen effect frequently causes strong absorption bands from 14 coarsely ground particles to be distorted due to the change in refractive 15 index associated with the anomalous dispersion of the refractive index 16 through the absorption region. 17 For Peer Review Only 18 Source: [6]. 19 20 21 505. Christiansen filter 22 23 Optical filter based on the Christiansen effect. 24 25 Note: Such filters have been made from quartz particles in air, immersed in CCl4, 26 or immersed in mixtures of CCl and CS . 27 4 2 28 29 Source: [6]. 30 31 506. circular dichroism, (CD) 32 33 Measurement principle [VIM 2.4] of molecular spectroscopy based on the difference in 34 absorbance of left- and right-handed circularly polarised light by a material as a 35 36 function of wavelength. 37 38 Note 1: Circular dichroism is measured as kL-kR where kL and kR are the absorption 39 indices of the sample for left and right circularly polarized radiation 40 respectively. Some authors use the linear decadic absorption coefficient or 41 molar decadic absorption coefficient to calculate circular dichroism instead 42 43 of the absorption index. 44 45 Note 2: Like the absorption indices (kL, kR), circular dichroism changes with 46 wavenumber. 47 48 Note 3: Most biological molecules, including proteins and nucleic acids, are chiral 49 and show circular dichroism in their ultraviolet absorption bands, which 50 51 may be used as an indication of secondary structure. Metal centres that are 52 bound to such molecules, even if they have no inherent chirality, usually 53 exhibit CD in absorption bands associated with ligand-based or ligand- 54 metal charge-transfer transitions. CD is frequently used in combination with 55 absorption and magnetic circular dichroism studies to assign electronic 56 transitions. 57 58 59 Source: [6], [61] p 1265. 60

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1 2 3 507. coherent anti-Stokes Raman spectroscopy, (CARS) 4 5 6 Measurement method [VIM 2.5] of Raman spectroscopy that uses third-order 7 susceptibility and is one of several four-wave mixing spectroscopies. The excitation is 8 through lasers of wavenumber �1 and �2 which coincide spatially and temporally in the 9 sample and produce an output laser of wavenumber �3 = 2�1 ― �2. 10 11 12 Note 1: Experimentally, �1 is kept constant and �2 is scanned. A laser beam output 13 is observed at the wavenumber for anti-Stokes Raman scattering �1 + �M 14 when �1 ― �2 = �M, where �M is the wavenumber of an active vibration in 15 the sample. 16 17 18 Note 2: TheFor Raman Peer scattered radiationReview emerges asOnly a laser beam instead of being 19 scattered into three dimensions, thus greatly enhancing the sensitivity over 20 that in normal Raman scattering. 21 22 Source: [6]. 23 24 25 508. collision broadening 26 27 See: pressure broadening. 28 29 509. combination transition 30 31 32 Transition in which more than one vibration changes its degree of excitation; i.e., in 33 which more than one vibrational quantum number changes. 34 35 Note 1: Combination band results from a combination transition. 36 37 Note 2: Combination transitions are either sum or difference transitions, although 38 39 some authors restrict them to sum transitions. 40 41 Source: [6]. 42 43 510. constant resolution tunnelling intensity 44 45 See: normalized tunnelling intensity. 46 47 48 511. continuous scan interferometer 49 50 Interferometer in which the optical path difference is continually changed. 51 52 Note 1: Continuous scan interferometer is typically used for Fourier-transform 53 54 infrared spectroscopy. 55 56 Note 2: In slow scan interferometers, the rate of change of optical path difference is 57 less than 0.05 cm s–1 and a mechanical chopper or some other ancillary 58 modulation is frequently used to provide an adequate modulation 59 frequency. 60

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1 2 3 Note 3: In rapid-scan interferometers, the rate of change of optical path difference 4 is above 0.05 cm s–1, high enough that no additional modulation is needed. 5 6 7 Source: [6]. See also: step-scan interferometer. 8 9 512. Coriolis coupling 10 11 Coupling between rotational and vibrational molecular motion caused by Coriolis 12 13 forces. 14 15 Source: [6]. 16 17 513. Coriolis force 18 For Peer Review Only 19 In vibrational theory, the motion of a polyatomic molecule is usually initially regarded 20 21 as the independent superposition of a rotation and a vibration, with the vibration 22 considered in a coordinate system that rotates with the molecule. This initial treatment 23 must be corrected for centrifugal forces and for Coriolis forces. The Coriolis force on 24 an atom is given by FCoriolis = 2m va ω sinφ, where m is the mass of the atom, va is its 25 apparent velocity in the rotating coordinate system, ω is the angular velocity of the 26 27 coordinate system, and φ is the angle between the velocity vector and the axis of 28 rotation. 29 30 Note: SI unit: N. 31 32 Source: [6]. 33 34 35 514. correlation splitting 36 See: Davydov splitting. 37 38 515. critical angle, θc 39 40 Smallest angle of incidence at which total internal reflection occurs. 41 42 � 43 Note: If �2 > �1 are the refractive indices at the boundary, sin �c = 1 �2. 44 45 Source: [6]. 46 47 48 516. crystal field splitting 49 50 The removal of a degeneracy of the energy levels of molecules or ions due to the lower 51 site symmetry created by a crystalline environment. 52 53 Note 1: The term site splitting may be used more generally to refer to any effect due 54 to differences in energies of locations on a crystal. 55 56 57 Note 2: ‘Crystal field splitting’ is sometimes incorrectly used synonymously with 58 the term ‘ligand field splitting’. 59 60 Source: [62] p 2234. [6]. See also: site splitting.

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1 2 3 517. Davydov splitting 4 correlation splitting 5 6 exciton splitting 7 8 Appearance of more than one spectral band in the spectrum of a crystal when only one 9 is seen in that of the gas due to intermolecular vibrational coupling. 10 11 Note: Davydov splitting arises from the dynamic intermolecular forces in the 12 13 crystal. 14 15 Source: [6]. 16 17 518. deformation vibration 18 For Peer Review Only 19 Vibration in which the dominant change from equilibrium is in one or more valence 20 21 angles. 22 23 Source: [6]. 24 25 519. depolarization ratio, ρ 26 27 28 Raman intensity with the electric vector of the scattered radiation perpendicular to that 29 of the incident radiation divided by the Raman intensity with electric vectors parallel. 30 31 Note: In normal Raman scattering with linearly polarized exciting radiation, ρ ≤ 32 0.75 for totally symmetric vibrations and ρ = 0.75 for all other vibrations. 33 34 35 Source: [6]. 36 37 520. depolarized Raman band 38 39 Raman band with depolarization ratio ρ = 0.75 for linear polarized incident radiation in 40 41 normal Raman spectroscopy. 42 43 Source: [6]. See polarized Raman band. 44 45 521. depth of penetration in attenuated total reflection, dp 46 47 48 Distance from the boundary with the internal reflection element at which the mean 49 square electric field intensity of the evanescent wave, i.e., the intensity of a collimated 50 radiation beam, is reduced to 1/e of its value at the boundary. 51 52 Note 1: In photoacoustic spectroscopy (PAS), an analogous definition may be cited 53 for strongly absorbing samples. For weakly absorbing photoacoustic 54 samples, the depth of penetration is given by the thermal diffusion depth. 55 56 In practice, the depth below the surface that gives rise to most of the 57 measured photoacoustic spectrum is the lesser of the thermal diffusion 58 depth and the optical absorption depth. 59 60 Note 2: SI unit: m. Common unit: µm.

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1 2 3 Source: [6]. See attenuated total reflection. 4 5 6 522. dichroism 7 8 Dependence of absorbance on the type of polarization of the measuring beam. 9 10 Source: [8] p 324. See circular dichroism. 11 12 13 523. difference transition 14 15 Combination transition which does not start at the ground state and in which at least 16 one vibration decreases and at least one vibration increases its degree of excitation; i.e., 17 a transition inFor which morePeer than one Review vibrational quantum Only number changes and at least 18 one becomes smaller. 19 20 21 Note: A difference band or difference tone results from a difference transition. 22 23 Source: [6]. 24 25 524. divided spinning cell 26 27 28 Measuring instrument [VIM 3.1] for Raman spectroscopy incorporating a dish-shaped 29 cell that is divided by a vertical partition through its middle to allow different liquids in 30 its two halves. It is rotated about a vertical axis through its centre and the Raman 31 scattered radiation from each half is measured alternately. With a standard liquid in 32 one half and a sample in the other it is used to determine Raman scattering intensities 33 relative to the standard. 34 35 36 Source: [6]. 37 38 525. dynamic spectrum 39 40 Spectrum of a material under the influence of an applied external perturbation 41 42 represented by a variable τ, relative to a reference spectrum. 43 44 Note: The reference spectrum may be chosen in many ways; e.g., it may be the 45 average over τ, of the observed spectrum, or it may be zero. See also: two- 46 dimensional correlation spectroscopy and two-dimensional correlation 47 spectrum 48 49 50 Source: [6]. 51 52 526. elastic scattering 53 54 See: Rayleigh scattering. 55 56 57 527. electrical anharmonicity 58 anharmonicity 59 60

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1 2 3 Influence of terms that are of 2nd and higher order in Q in the expansion of the 4 electrical dipole moment. 5 6 7 Note: Electrical anharmonicity should not be confused with mechanical 8 anharmonicity. 9 10 Source: [6]. See Note in electrical dipole moment. See also: electrical harmonicity. 11 12 13 528. electrical harmonicity 14 harmonicity 15 16 Influence of the linear term, Σk (∂µ/∂Qk) Qk, in the expansion of the electrical dipole 17 moment. 18 For Peer Review Only 19 20 Note: Electrical harmonicity should not be confused with mechanical 21 harmonicity. 22 23 Source: [6]. See Note in electrical dipole moment. 24 25 529. electron energy loss spectroscopy, (EELS) 26 27 28 Measurement method [VIM 2.5] of molecular spectroscopy in which a constant-energy 29 beam of electrons passes through or is reflected from a sample and the energy 30 distribution in the transmitted or reflected beam is analysed to give a spectrum of 31 number of electrons against electron energy loss. 32 33 Note: EELS is used for the study of electronic states and has an energy resolution 34 35 of 0.25 eV or better (corresponding to an approximate wavenumber of –1 36 2 000 cm ). 37 38 Source: [6]. 39 40 530. electro-optic parameter, (EOP) 41 42 equilibrium charge, charge flux, (ECCF) 43 44 Characteristic quantity used in the analysis of absolute infrared intensity data chosen on 45 the assumption that the electric dipole moment of the molecule can be described as the 46 vector sum of bond dipole moments. 47 48 o 49 Note: The original EOPs were �� , the equilibrium bond moment, and ∂μk/∂Rt, the 50 change in the electric dipole moment of bond k with change in internal 51 displacement coordinate t. A later and completely equivalent formulation 52 o uses equilibrium atomic charges, �� , and charge fluxes, ∂qα/∂Rt, which are 53 also called EOPs as well as ECCF for equilibrium charge, charge flux. 54 55 56 Source: [6]. 57 58 59 60

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1 2 3 531. ellipsometry 4 5 6 Measurement method [VIM2.5] for refractive index of a reflecting material. 7 8 Note: Radiation that is linearly polarized oblique to the surface becomes 9 elliptically polarized after reflection at non-normal incidence. The 10 ellipticity is obtained from measurements of the intensity and polarization 11 of the incident and reflected radiation. 12 13 14 Source: [6]. 15 16 532. ellipticity, ψ 17 For Peer Review Only 18 Degree to which linearly polarized incident electromagnetic radiation becomes 19 elliptically polarized in an absorbing optically active medium. 20 (� ― � ) L R 21 tan � = R L (�R + �L) = tanh (� ― � )�� 22 where ER and EL are the electric vectors of right and left circularly polarized radiation, 23 kL and kR are the absorption indices of the sample for left and right circularly polarized 24 radiation, λ is the wavelength of the radiation and l is the path-length through the 25 26 medium. 27 28 Note: SI unit: rad = 1. 29 30 Source: [6]. 31 32 533. equilibrium charge, charge flux, (ECCF) 33 34 35 See: electro-optic parameter. 36 37 534. étendue 38 39 See: optical throughput of a spectrometer. 40 41 42 535. evanescent wave 43 44 Part of a standing-wave normal to a reflecting surface that extends beyond the 45 reflecting surface when an electromagnetic wave undergoes total internal reflection. 46 47 48 Source: [6]. 49 50 536. Evans Hole 51 52 Unexpected minimum or hole in a broad absorption band due to a gap being created in 53 a broad distribution of states by Fermi resonance. 54 55 56 Source: [6]. 57 58 59 60

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1 2 3 537. excitation profile 4 5 6 Graph of Raman intensity at the desired Raman shift against wavenumber of the 7 excitation. 8 9 Source: [6]. 10 11 538. exciton splitting 12 13 14 See: Davydov splitting. 15 16 539. external reflection spectroscopy 17 For Peer Review Only 18 Measurement method [VIM 2.5] of spectroscopy in which radiation is reflected from a 19 sample of higher refractive index than that of the incident medium. 20 21 22 Source: [6]. 23 24 540. extraordinary wave 25 extraordinary ray 26 27 28 In a uniaxial crystal electromagnetic radiation with electric vector oblique to the optic 29 axis and which does not obey the normal laws of refraction. 30 31 Note: In uniaxial crystals the optic axis coincides with the symmetry axis. The 32 refractive index of the crystal is the same in all directions perpendicular to 33 the optic axis but is different along the optic axis. Consequently, 34 35 electromagnetic rays or waves that do not travel along the optic axis 36 experience different refractive indices in different directions perpendicular 37 to their direction of propagation. Two waves result, one has its electric 38 vector perpendicular to the optic axis and forms the ordinary wave. The 39 other is the extraordinary wave. 40 41 Source: [6]. 42 43 44 541. far-infrared radiation 45 46 See: infrared radiation. 47 48 542. Fermi resonance 49 50 51 Cubic anharmonic resonance (see: anharmonicity), i.e. any interaction caused by cubic 52 terms in the vibrational potential energy. 53 54 Note 1: Traditionally, Fermi resonance was defined as the anharmonic interaction 55 between a fundamental state and one or more overtone or combination 56 transitions. 57 58 59 60

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1 2 3 Note 2: Fermi resonance is usually identified by the presence of more than one band 4 of comparable intensity when only one fundamental is expected. Also seen 5 6 as an Evans hole. 7 8 Source: [6]. 9 10 543. finesse of a spectrometer 11 12 13 Free spectral range divided by resolution. 14 15 Source: [6]. 16 17 544. fingerprint bands 18 For Peer Review Only 19 Infrared and Raman bands that are characteristic of a particular molecule rather than a 20 21 functional group. 22 23 Source: [6]. 24 25 545. fingerprint region 26 27 28 Region of a spectrum that contains fingerprint bands as well as bands with 29 characteristic group frequencies. 30 31 Note: The fingerprint region is often associated with the region of the mid- 32 infrared or Raman spectrum of wavenumbers between 1500 cm–1 and 33 400 cm–1. (See: infrared radiation). 34 35 36 Source: [6]. 37 38 546. Fourier-transform infrared (FT-IR) spectroscopy 39 Fourier-transform infrared spectrometry 40 41 Infrared spectroscopy in which a Fourier-transform spectrometer is used to separate 42 43 the transmitted radiation into its component wavenumbers. 44 45 547. Fourier-transform Raman spectroscopy 46 Fourier-transform Raman spectrometry 47 48 Raman spectroscopy in which a Fourier-transform spectrometer is used to separate the 49 50 scattered radiation into its component wavenumbers. 51 52 Note: This technique usually uses near-infrared excitation. 53 54 Source: [6]. 55 56 548. Fourier-transform spectrometer 57 58 59 Spectrometer in which radiation is separated into its component wavenumbers by 60 Fourier transformation of the interferogram produced by an interferometer.

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1 2 3 Source: [6]. See also: Fourier-transform spectroscopy. 4 5 6 549. free spectral range, Δ� 7 8 For a Fabry-Perot or laser cavity, wavenumber interval between successive longitudinal 9 cavity modes of vibration; ∆� = ½ n l, where l is the cavity spacing and n is the 10 refractive index of the material in the cavity. 11 12 –1 13 Note: SI unit: m 14 15 Source: [6]. 16 17 550. frustrated total internal reflection spectroscopy 18 For Peer Review Only 19 20 See: attenuated total reflection spectroscopy. 21 22 551. grazing incidence 23 24 Angle of incidence of a beam of electromagnetic radiation greater than 70o. 25 26 o 27 Note: Ideally the angle of incidence should be greater than 80 28 29 Source: [6]. 30 31 552. group frequency 32 33 34 Frequency in vibrational spectroscopy that is characteristic of a particular chemical 35 functional group. 36 37 Note: The frequency is usually given as a wavenumber. 38 39 Source: [6]. 40 41 42 553. harmonic constant, ωe, ωk 43 harmonic wavenumber 44 45 Coefficient of (v + ½) in the vibrational term value, determined by the harmonic terms 46 in the vibrational potential energy. 47 48 –1 –1 49 SI unit: m ; Common unit: cm . 50 51 Source: [6]. 52 53 554. harmonicity 54 55 56 See: electrical harmonicity. 57 58 555. high resolution electron energy loss spectroscopy, (HREELS) 59 vibrational electron energy loss spectroscopy, (VEELS) 60

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1 2 3 Electron energy loss spectroscopy in which the energy resolution is between 1 and 5 4 meV (wavenumber 8 cm–1 and 40 cm–1). 5 6 7 Note: HREELS is used to detect vibrational motion. 8 9 Source: [6]. 10 11 556. homogeneous line-broadening 12 13 homogeneous broadening 14 15 Line-broadening by mechanisms that affect every molecule of the same species in the 16 sample in the same way. 17 For Peer Review Only 18 Note: Such mechanisms do not require an ensemble of spectroscopically non- 19 equivalent molecules of the same species. Such mechanisms are the 20 21 natural line width, which is usually negligible in vibrational spectroscopy, 22 and intra- or intermolecular interactions, including anharmonic vibrational 23 interactions (see: anharmonicity), that reduce the lifetime of the excited 24 state. 25 26 Source: [6]. 27 28 29 557. hot transition 30 31 Electronic transition between an excited state and a state in which all vibrational 32 quantum numbers are the same or greater. 33 34 Note 1: A hot band arises from a hot transition. 35 36 37 Note 2: A hot transition has the same changes in vibrational quantum numbers as a 38 fundamental, overtone transition, or sum transition but it originates in an 39 excited vibrational state not the ground state. 40 41 Source: [6]. 42 43 44 558. hyperpolarizability, β 45 46 Coefficient of the second order term in the relation between the electric dipole moment 47 2 µ of a molecule and the electric field E which acts on the molecule, µ = µo + αΕ + βE 48 3 49 + γE . 50 51 Note 1: Hyperpolarizability is a scalar for isotropic entities and a 3×3 tensor for 52 others. 53 54 Note 2: SI unit: C3 m3 J–2. 55 56 57 See polarizability. 58 59 60

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1 2 3 559. hyper-Raman spectroscopy, (HRS) 4 5 6 Raman spectroscopy in which scattering occurs through hyperpolarizabilities. A two- 7 photon technique in which an intense pulsed beam of electromagnetic radiation is 8 focused onto the sample. When sufficient power is present in the pulse, two photons 9 may interact with the one molecule to create a virtual state at double the frequency of 10 the laser excitation. Raman scattering from this virtual state to an excited vibrational 11 state of the ground state then occurs. 12 13 14 Note: Intense scattering is obtained from less symmetric vibrations and from 15 some vibrations not intense in Raman scattering. 16 17 Source: [6]. 18 For Peer Review Only 19 560. hyperspectral imaging 20 21 22 Measurement method [VIM 2.5] to obtain information about the spatial composition of 23 a sample by obtaining a spectrum at each spatially resolved point of the sample. 24 25 Source: [6]. 26 27 28 561. improper rotation axis, Sn 29 30 In spectroscopy, a rotation-reflection axis, which is a symmetry element such that 31 rotation by 2π/n about the axis followed by reflection through a plane perpendicular to 32 the axis transforms an object into itself. 33 34 35 Note: In crystallography, a rotation-inversion axis, which is a symmetry element 36 such that rotation by 2π/n about the axis followed by inversion through the 37 centre of symmetry transforms an object into itself. 38 39 Source: [6]. 40 41 42 562. inelastic electron tunnelling spectroscopy, (IETS) 43 44 Measurement method [VIM 2.5] of vibrational spectroscopy to obtain spectra of 45 molecules on metal oxide surfaces. 46 47 Note: IETS yields vibrational spectra of adsorbates with high resolution (< 0.5 48 13 49 meV) and low limit of detection (< 10 molecules are required to provide a 50 spectrum). 51 52 Source: [63, 64]. 53 54 563. infrared (IR) radiation 55 infrared 56 57 58 Electromagnetic radiation of wavelength between approximately 780 nm and 1 000 µm 59 or of wavenumber between approximately 13 000 cm–1 and 10 cm–1. 60

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1 2 3 Note 1: The infrared range is sub-divided into three regions: near-infrared: 780 nm 4 – 2.5 μm (12 800 – 4000 cm–1); mid-infrared: 2.5 – 25 μm (4 000 – 400 cm– 5 1 –1 6 ) and far infrared: 25 – 1000 μm (400 – 10 cm ). See Table 1. 7 8 Note 2: The wavelength regions given are commonly used in chemistry and relate 9 to working ranges of infrared spectrometers. Note that in other disciplines 10 (e.g. astronomy) the terms are defined for different ranges. 11 12 13 Note 3: If there is no ambiguity the term ‘infrared’ is used for the mid-infrared 14 region. 15 16 See: infrared spectroscopy, Raman spectroscopy. 17 For Peer Review Only 18 564. infrared reflection-absorption spectroscopy, (IRRAS) 19 20 21 See: reflection-absorption infrared spectroscopy. 22 23 565. infrared spectroscopy 24 25 Measurement principle [VIM 2.4] of molecular spectroscopy using infrared radiation. 26 27 28 Note: Without qualification, ‘infrared spectroscopy’ usually refers to use of the 29 mid-infrared (wavelength range 2.5 – 25 µm, wavenumber range (4 000 – 30 400 cm–1) region of the electromagnetic spectrum. 31 32 566. inhomogeneous broadening 33 34 35 Line-broadening by mechanisms that arise from an ensemble of spectroscopically non- 36 equivalent molecules of the same species. Such molecules exist, for example, when 37 molecules occupy non-equivalent sites in a condensed phase, and when gaseous 38 molecules have different velocities and, thus, shift the observed wavenumber 39 differently through the Doppler effect. 40 41 42 Source: [6]. 43 44 567. interference fringes 45 channel fringes 46 47 Sinusoidal intensity variation due to interference of electromagnetic radiation that 48 undergoes multiple reflection between two flat and parallel surfaces. 49 50 51 Note 1: Interference fringes are frequently observed in the transmission spectrum of 52 a cell with flat windows and in non-scattering polymer films. 53 54 Note 2: A spectrum of interference fringes is termed a channel spectrum. 55 56 57 Source: [6]. 58 59 568. interference record 60 interference function

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1 2 3 Record of the signal from the detector of a two-beam interferometer as the optical path 4 difference between the two beams is varied. 5 6 7 Note: The interference record contains a part that is constant and a part that varies 8 with the path difference. 9 10 Source: [6]. 11 12 13 569. interferogram 14 15 Pattern formed by wave interference produced by an interferometer, especially one 16 represented on a screen or chart recorder. 17 For Peer Review Only 18 570. interferometer 19 20 21 Measuring instrument [VIM 3.1] in which two beams of electromagnetic radiation 22 interfere with each other after passing through different optical paths. 23 24 Note: In vibrational spectroscopy the output is usually an interference record, viz, 25 intensity versus path difference (see interferogram). 26 27 28 Source: [6]. 29 30 571. internal reflection 31 32 Reflection of electromagnetic radiation from a material of lesser refractive index than 33 that of the incident medium. 34 35 36 Source: [6]. 37 38 572. internal reflection element 39 40 Transparent or semi-transparent material of high refractive index that carries infrared 41 radiation to a sample in internal reflection and attenuated total reflection 42 43 measurements. 44 45 Note: The sample is mounted in optical contact with the element. 46 47 Source: [6]. 48 49 50 573. internal reflection spectroscopy, (IRS) 51 52 See: attenuated total reflection spectroscopy. 53 54 574. inverse Raman Scattering 55 56 57 Raman scattering showing absorption when Stokes Raman scattering exceeds anti- 58 Stokes Raman scattering, in an experiment in which a sample is simultaneously 59 illuminated by coincident beams from a continuum source and a pulse laser at �0 . 60 Energy is absorbed from the continuum at �0 + �s where �s is the wavenumber of a

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1 2 3 Raman-active vibration in the sample which is excited by this process, and this energy 4 is emitted at � . 5 0 6 7 Source: [6]. 8 9 575. inverse spatially offset Raman spectroscopy 10 11 12 Variant of spatially offset Raman spectroscopy in which a sample is illuminated with a 13 ring of laser light and the Raman scattering is collected from the centre of the ring. 14 15 576. IRTRAN ™ 16 17 Kinds of crystalFor transparent Peer to infrared Review radiation used Only as windows and filters in 18 infrared spectroscopy. 19 20 21 Note 1: IRTRAN 1 to IRTRAN 5 are hot-pressed forms of MgF2, CdF2, MgO, 22 ZnSe and ZnS, respectively. 23 24 Note 2: IRTRAN is a registered trade mark of Eastman Kodak Co. 25 26 27 Source: [6]. 28 29 577. Jacquinot stop 30 J-stop 31 32 Aperture in the optics of a Fourier-transform spectrometer, typically between the 33 source and the interferometer, designed to be the limiting aperture when no other 34 35 optical element such as the detector serves this purpose. 36 37 Source: [6]. 38 39 578. kinetic coupling 40 41 42 Coupling of vibrational displacements through terms in the vibrational kinetic energy. 43 44 Note: Two displacement coordinates must share a common atom if they are to 45 undergo kinetic coupling. 46 47 Source: [6]. 48 49 50 579. KRS-5 51 52 Eutectic (42% TlBr, 58% TlI) mixture of thallium bromide and thallium iodide 53 transparent to infrared radiation used as window in infrared spectroscopy. 54 55 Note: KRS-5 transmits well down to 200 cm–1. It is practically insoluble in water 56 57 but its refractive index is rather high (approximately 2.35). It is rather 58 plastic and deforms with time, and it is poisonous. 59 60 Source: [6].

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1 2 3 580. Kubelka Munk function 4 remission function 5 6 2 7 f(R∞) = (1 – R∞) /2R∞, where R∞ is the diffuse reflectance from a sample of infinite 8 depth. 9 10 Note: Theoretically f(R ) equals the ratio of the linear decadic absorption 11 ∞ 12 coefficient to the scattering coefficient. Under the assumptions of the 13 Kubelka Munk theory, if the scattering coefficient at a given wavenumber is 14 a constant for a given set of samples, f(R∞) is directly proportional to the 15 product of the absorption coefficient and concentration of each component 16 of a mixture, analogous to the behaviour of absorbance under Beer’s law. 17 18 For Peer Review Only 19 Source: [6]. See also: volume reflection. 20 21 581. Kubelka Munk reflection 22 23 See: volume reflection. 24 25 582. lifetime broadening 26 27 28 Homogeneous line-broadening due to the limited lifetime of energy states involved in a 29 transition. 30 31 Note: The lifetime may be limited by the natural lifetime, by collisions, as in 32 pressure broadening, or by anharmonic vibrational interactions as in 33 34 phonon-phonon collisions in solids. 35 36 Source: [6]. 37 38 583. lifetime of an excited state 39 lifetime 40 41 42 Duration of existence of a molecule in an excited state before returning to a lower 43 energy level (usually the ground state). 44 45 584. line width 46 linewidth 47 48 49 Extent of a spectral line usually measured as the full width at half maximum. 50 51 Note: Line width may be expressed in terms of wavelength, wavenumber, or 52 frequency. 53 54 See also: natural line width. 55 56 57 585. local mode of vibration 58 local mode 59 60 Mode of vibration localized in one type of bond.

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1 2 3 Note: For highly excited CH stretching vibrations anharmonic interactions mix 4 the normal modes of vibration to the point that each observed mode of 5 6 vibration behaves as a local mode 7 8 Source: [6]. 9 10 586. local molar polarizability, �m(�) 11 12 molar polarizability 13 14 Defined under the assumption of the Lorentz local field by the Lorentz-Lorenz formula: 15 �(�) ― 1 �2(�) ― 1 16 �m(�) = 3�m�0 = 3�m�0 where V is the molar volume and � and � �(�) + 2 �2(�) + 2 m 17 For Peer Review Only 18 are the complex dielectric constant and refractive index, respectively. To allow 19 ” description of absorption, �m(�) is complex: �m(�) = �m′ (�) + i�m(�). 20 21 22 Note 1: The imaginary molar polarizability shows the absorption band free from 23 long range dielectric effects which distort the band shapes of very strong 24 absorptions. 25 26 Note 2: SI unit: J–1 C2 m2 mol–1. 27 28 29 Source: [6]. See also: polarizability. 30 31 587. mechanical anharmonicity 32 anharmonicity 33 34 Influence of cubic and higher-order terms in vibrational potential energy. 35 36 37 Note: Mechanical anharmonicity should not be confused with electrical 38 anharmonicity. 39 40 Source: [6]. 41 42 43 588. mechanical harmonicity 44 harmonicity 45 46 Influence of quadratic terms in vibrational potential energy. 47 48 Note: Mechanical harmonicity should not be confused with electrical 49 harmonicity. 50 51 52 Source: [6]. 53 54 589. mid-infrared radiation 55 56 See: infrared radiation. 57 58 59 60

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1 2 3 590. Mie scattering 4 5 6 Scattering of electromagnetic radiation by particles with diameters that are greater than 7 or similar to the wavelength of the radiation but are too small to yield specular 8 reflection or diffuse reflection. 9 10 Source: [6]. 11 12 13 591. mode of vibration 14 vibration mode 15 mode 16 vibration 17 For Peer Review Only 18 Independent vibrational motion of a molecule. 19 20 21 Note: In vibrational spectroscopy ‘mode’ or ‘vibration’ is used for normal mode 22 of vibration. 23 24 Source: [6]. 25 26 592. molar ellipticity, Θ (t,λ) 27 28 29 Ellipticity divided by the amount concentration of the optically active absorbing 30 material and by the path-length at temperature t and wavelength λ. 31 32 Note: SI unit: rad m2 mol–1 33 34 35 Source: [6]. 36 37 593. multiplex advantage 38 39 Decrease in measurement uncertainty [VIM 2.26] obtained by measuring intensity at 40 many different wavelengths simultaneously, as is done, for example, in Fourier- 41 42 transform spectroscopy. 43 44 Source: [6]. 45 46 594. natural lifetime of an excited state, ∆t 47 48 49 Lifetime of an excited state of a molecule that is isolated from radiation fields and other 50 molecules or entities. 51 52 Note: The lifetime is limited by the probability of spontaneous emission to a 53 lower state. If an excited state, n can only emit spontaneously to a single 54 lower state m, the natural lifetime of state n equals the reciprocal of A , the 55 mn 56 Einstein transition probability of spontaneous emission. 57 58 Source: [6]. 59 60

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1 2 3 595. natural linewidth 4 5 6 Line width of a molecular spectral band that arises from the probability of spontaneous 7 emission in the absence of radiation fields and interaction with other molecules or 8 entities. 9 10 Note 1: The natural linewidth, measured as the full width half maximum equals 11 1/(2π c ∆t), where ∆t is the natural lifetime of the excited state. 12 o 13 14 Note 2: If the excited state n can only emit spontaneously to a single lower state m 15 –38 3 2 the natural linewidth is 1.86 × 10 ��〈m|µ|n〉 , when the transition 16 –1 17 wavenumber �� is in cm and the dipole moment µ is in Debye (1 D ≈ –30 18 3.335For 64 ×Peer10 C m). ReviewIn the infrared, typical Only natural linewidths are 19 approximately10–7 cm–1. 20 21 Source: [6]. 22 23 24 596. near-infrared radiation 25 near-IR 26 27 Infrared radiation of which vacuum wavenumbers range from approximately12 800 28 cm–1 to 4000 cm–1 and wavelengths range from approximately 780 nm to 2500 nm. 29 30 −1 31 Note: The region is often divided into the silicon region between 12 800 cm and −1 32 9000 cm (800 nm and 1100 nm) and the lead sulfide region between 9000 33 cm−1 and 4000 cm−1 (1100 nm and 2500 nm), where the names reflect the 34 common detector for the region. 35 36 Source: [6]. 37 38 39 597. non-dispersive infrared spectroscopies 40 41 Kinds of infrared spectroscopy in which the effect of the sample on the radiation from 42 the source is measured as a whole without exploring the dependence on wavenumber. 43 44 45 Note: These methods are mainly used to obtain adequate optical throughput for 46 process measurement and monitoring 47 48 Example: Two-dimensional infrared correlation spectroscopy. 49 50 Source: [6]. 51 52 53 598. normal coordinate, Qk 54 55 Formal mathematical description of a normal vibration. When the potential energy, V, 56 is harmonic and the kinetic energy, T, is calculated in the limit of infinitesimally small 57 displacements, the normal coordinates are defined as independent entities such that 58 ∑3� ― 6 2 ∑3� ― 6 2 59 � = ½ � = 1 �� and � = ½ � = 1 �� 60 th where λk is the k eigenvalue and � is ∂Q/∂t. Normal coordinate Qk is related to the

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1 2 3 internal displacement coordinates, R , through the elements, L = ∂R /∂Q of the kth 4 i ik i k 5 column of the eigenvector matrix L. Normal coordinates are not independent when the 6 potential energy is anharmonic, or the displacements are not infinitesimal. See also: 7 normal coordinate analysis and vibrational eigenvector. 8 9 Note: SI unit: kg1/2 m, Common unit u1/2 Å ≈ 4.07497 × 10–24 kg1/2 m. 10 11 Source: [6]. 12 13 14 599. normal coordinate analysis 15 16 Calculation of the normal modes of vibrations of a molecule or crystal under the 17 assumptions Forthat the potentialPeer energy Review is harmonic and Only the displacements from 18 equilibrium are infinitesimal. See also: normal coordinate and vibrational eigenvector. 19 20 21 Source: [6]. 22 23 600. normal dispersion of the refractive index 24 normal dispersion 25 26 Slow decrease of real refractive index of a material in a non-absorbing spectral region 27 28 far from regions of strong absorption as the wavenumber decreases. 29 30 Source: [6]. 31 32 601. normal incidence 33 34 ° 35 Incidence of a beam of electromagnetic radiation when the angle of incidence θ = 0 , 36 i.e., the incident radiation beam is normal to the surface. 37 38 Source: [6]. 39 40 602. normal mode of vibration 41 42 normal vibration mode 43 normal mode 44 normal vibration 45 46 One of the 3N – 6 (3N – 5 for a linear molecule) modes of vibration that would add to 47 give the total vibrational motion in a molecule if the interatomic potential were strictly 48 49 quadratic in the displacements from equilibrium. 50 51 Note: Normal modes of vibration is an idealized concept that has proved 52 extremely useful in analysing spectra in vibrational spectroscopy. 53 54 Source: [6]. 55 56 57 603. normal Raman scattering 58 59 See: Raman scattering 60

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1 2 3 604. normalized tunnelling intensity 4 constant resolution tunnelling intensity 5 6 7 Second differential of intensity with respect to bias voltage divided by first differential 8 of intensity with respect to bias voltage. 9 10 Note: Normalized tunnelling intensity is plotted against the bias voltage to report 11 inelastic electron tunnelling spectroscopy data. 12 13 14 Source: [6]. 15 16 605. null-balance (NTI) double beam spectrometer 17 For Peer Review Only 18 See: optical null double beam spectrometer. 19 20 21 606. numerical aperture, (NA) 22 23 For an optical fibre, no sin θα, where no is the refractive index of the exterior medium 24 and θα is the maximum input half angle that can support propagation. 25 26 Source: [6]. 27 28 29 607. optical absorption depth, μβ 30 31 Depth in a sample at which the intensity of an incident beam is reduced to 1/e of its 32 value at the surface of the sample. 33 34 35 Note 1: μβ is the reciprocal of the linear Napierian absorption coefficient. 36 37 Note 2: SI unit: m. Usually expressed as µm. 38 39 40 Source: [6]. 41 42 608. optical constants 43 44 Collective name for the real refractive index, n and the absorption index (imaginary 45 refractive index), k. 46 47 48 609. optical null double beam spectrometer 49 null-balance (NTI) double beam spectrometer 50 51 Spectrometer in which the ratio of the radiant power in the two beams at each 52 wavenumber is measured opto-mechanically by inserting a linear optical attenuator into 53 the reference beam until the two signals measured by the detector are equal, then 54 55 measuring the displacement of the optical attenuator. 56 57 Source: [6]. 58 59 60

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1 2 3 610. optical path difference, (OPD) 4 optical retardation 5 6 7 Path-length difference between the arms of a two-beam interferometer. 8 9 Note 1: The term optical retardation is derived from ‘phase retardation’ which 10 refers to the change in the phase of the electromagnetic radiation in the 11 interferometer. 12 13 14 Note 2: SI unit: m. Common unit: cm. 15 16 Source: [6]. 17 For Peer Review Only 18 611. optical rotatory dispersion, (ORD) 19 20 21 Wavelength dependence of the angle of rotation of the plane of linearly-polarized 22 radiation when transmitted through optically active materials. 23 24 Source: [6]. 25 26 612. optical throughput of a spectrometer, G 27 28 optical throughput 29 étendue 30 31 Volume in phase space, function of the area of the emitting source (S) and the solid 32 angle into which it propagates (Ω) . d2� = d� dΩ. 33 34 35 613. orbital mediated tunnelling spectroscopy, (OMTS) 36 37 Measurement method [VIM 2.5] of spectroscopy based on electron tunnelling in which 38 bands are observed in dI/dV spectra that are associated with resonance-like interactions 39 between the tunnelling electron and oxidized or reduced states of the molecular system 40 studied. 41 42 43 Note: OMTS is usually used for analysing data obtained from metal-insulator- 44 analyte-metal tunnel diodes or from the metal-analyte-tip structure in STM 45 (scanning tunnelling microscopy). 46 47 Source: [6]. 48 49 50 614. ordinary wave 51 ordinary ray 52 53 In a uniaxial crystal electromagnetic radiation with electric vector perpendicular to the 54 optic axis and which obeys the normal laws of refraction. 55 56 Note: In uniaxial crystals the optic axis coincides with the symmetry axis. The 57 58 refractive index of the crystal is the same in all directions perpendicular to 59 the optic axis but is different along the optic axis. Consequently, 60 electromagnetic rays or waves that do not travel along the optic axis

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1 2 3 experience different refractive indices in different directions perpendicular 4 to their direction of propagation. Two waves result, one has its electric 5 6 vector perpendicular to the optic axis and forms the ordinary wave. The 7 other is the extraordinary wave. 8 9 Source: [6]. 10 11 615. overtone transition 12 13 14 Transition between the ground state and a state in which a single mode of vibration is 15 multiply excited. 16 17 Note: An overtone band results from an overtone transition. 18 For Peer Review Only 19 20 Example: Transition from the ground state to the state in which vi ≥ 2, vj≠i = 0. 21 22 Source: [6]. 23 24 616. pATR spectrum 25 deprecated: absorbance spectrum 26 27 28 −log10 of the spectrum obtained in attenuated total reflection spectroscopy. 29 30 Note: The term is used to avoid the confusing, but common and incorrect, practice 31 of calling it the absorbance spectrum. 32 33 34 Source: [6]. 35 36 617. photoacoustic saturation 37 38 Condition in photoacoustic spectroscopy in which all bands with greater than a certain 39 absorption intensity appear to have the same intensity. 40 41 42 Note: Photoacoustic saturation arises when the sample is optically opaque and 43 thermally thin, i.e., when the thermal diffusion depth, L, is greater than the 44 optical absorption depth, µβ, and less than the sample thickness. The 45 condition may be relieved by increasing the modulation frequency 46 sufficiently that L becomes less than µ , i.e., that the sample becomes 47 β 48 thermally thick. 49 50 Source: [6]. 51 52 618. photoacoustic spectroscopy, (PAS) 53 54 Measurement method [VIM 2.5] of spectroscopy in which the absorption of 55 56 electromagnetic radiation by the sample is detected by the emission of sound generated 57 by a thermal pressure wave in the sample. 58 59 Source: [6]. 60

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1 2 3 619. photothermal spectroscopy 4 5 6 Measurement method [VIM 2.5] of spectroscopy in which the absorption of 7 electromagnetic radiation by a sample is detected as a result of the heat generated by 8 the absorption. 9 10 Source: [6]. 11 12 13 620. polarizability, α 14 polarizability volume 15 16 Coefficient of the first order term in the relation between the electric dipole moment µ 17 2 of a moleculeFor and the Peerelectric field Review E which acts on theOnly molecule, µ = µo + αΕ + βE + 18 3 19 γE . 20 21 Note 1: Polarizability is a scalar for isotropic entities and a 3×3 tensor for others. 22 23 Note 2: SI unit: J–1 C2 m2 24 25 26 Note 3: The term ‘polarizability volume’ results when polarizability is defined in -1 2 27 equations under the esu or Gaussian system. To obtain the SI unit J C 2 28 m , the polarizability volume must be multiplied by 4πεo before converting 29 3 the volume unit to m . εo is the permittivity of vacuum. 30 31 32 Source: [6]. See also: hyperpolarizability, local molar polarizability. 33 34 621. polarized Raman band 35 36 Raman band with depolarization ratio ρ ≤ 0.75 for linear polarized incident radiation in 37 normal Raman spectroscopy. 38 39 40 Source: [6]. See also: depolarized Raman band. 41 42 622. potential coupling 43 44 Coupling of vibrational displacements through terms in the vibrational potential 45 46 energy. The second-order (quadratic) terms cause harmonic potential coupling while 47 the cubic and higher terms cause anharmonic potential coupling. 48 49 Source: [6]. See also: harmonicity, anharmonicity. 50 51 623. p-polarization 52 transverse magnetic (TM) polarization. 53 54 55 Polarization when electromagnetic radiation is incident upon a surface with its electric 56 vector in the plane of incidence and, therefore, inclined to the reflecting surface unless 57 the incidence is normal. 58 59 Source: [6]. 60

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1 2 3 624. pressure broadening 4 collision broadening 5 6 7 Increase in the line width of a spectral line of a gas due to molecular collisions and 8 other intermolecular interactions that reduce the lifetime of an excited state. 9 10 Note: At pressures sufficiently low that the line width is far smaller than the line 11 wavelength, the line width increases linearly with pressure, the broadening 12 13 is homogeneous and the line shape is Lorentzian. 14 15 Source: [6]. 16 17 625. quantum cascade laser, (QCL) 18 For Peer Review Only 19 Laser that emits mid-infrared radiation. 20 21 22 Note: A QCL can be used as a source for infrared spectroscopy. 23 24 626. Raman band 25 26 Spectral band in Raman spectroscopy. 27 28 29 627. Raman optical activity, (ROA) 30 31 Phenomenon that vibrations in chiral molecules and materials Raman-scatter right 32 circularly polarized incident radiation to a different extent than left circularly polarized 33 incident radiation. 34 35 36 In practice, the circular polarization of the exciting beam, or of the scattered beam, or 37 of both beams simultaneously, may be selected. Raman optical activity is usually 38 specified as ‘right minus left’ circular polarizations, in unfortunate contrast to the ‘left 39 minus right’ specification that is universal in vibrational circular polarization and other 40 forms of optical activity. 41 42 43 Source: [6]. 44 45 628. Raman scattering 46 normal Raman scattering 47 48 Inelastic scattering of electromagnetic radiation by molecules which are excited to 49 50 higher energy levels. 51 52 Note 1: Normal Raman scattering occurs through changes in polarizability of a 53 molecule during a vibration, not the hyper-polarizabilities, and is excited by 54 radiation that is not in resonance with electronic transitions in the sample. 55 56 Note 2: The energy of the scattered photon can be lesser (Stokes Raman scattering) 57 58 or greater (anti-Stokes Raman scattering) than that of the incident photon. 59 60

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1 2 3 629. Raman shift 4 5 6 Difference in wavenumber between the incident and scattered electromagnetic 7 radiation in Raman spectroscopy. 8 9 Note: SI unit: m–1. Common unit: cm–1. 10 11 Source: [6]. 12 13 14 630. Raman spectroscopy 15 16 Measurement principle [VIM 2.4] of molecular spectroscopy based on Raman 17 scattering. 18 For Peer Review Only 19 Note: Raman scattered light occurs at wavelengths that are shifted from the 20 21 incident light by the energies of molecular vibrations. 22 23 631. Raman spectrum 24 25 Graph of the intensity of scattered electromagnetic radiation in Raman spectroscopy 26 against Raman shift. 27 28 –1 29 Note: Commonly a Raman spectrum is obtained between approximately 100 cm 30 and 3500 cm–1 and is a complement its counterpart mid-infrared spectrum. 31 32 632. Raman wavenumber shift, �� 33 34 35 Wavenumber of exciting electromagnetic radiation minus wavenumber of the scattered 36 radiation. 37 38 Note 1: SI unit: m–1; Common unit: cm–1. 39 40 Note 2:Δ� is positive for Stokes Raman scattering and negative for anti-Stokes 41 42 Raman scattering. 43 44 Source: [6]. 45 46 633. rapid-scan Fourier-transform infrared spectroscopy 47 48 Fourier-transform infrared spectroscopy in which the optical path difference is 49 –1 50 continually changed at a rate ≥ 0.05 cm s . 51 52 Source: [6]. See also: continuous scan interferometer. 53 54 634. Rayleigh scattering 55 elastic scattering 56 57 58 Light scattering in which the incident and scattered radiation has the same frequency. 59 60

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1 2 3 635. reflection-absorption at grazing incidence 4 5 6 Reflection-absorption with very thin layers of an absorbing material on a metallic o o 7 substrate and the angle of incidence between 70 and 90 ; 8 9 Note: As the incident radiation beam travels nearly parallel to the sample surface, 10 the electric vector of the radiation is then either parallel or nearly 11 perpendicular to the surface. 12 13 14 Source: [6]. See reflection-absorption infrared spectroscopy. 15 16 636. reflection-absorption infrared spectroscopy, (RAIRS) 17 infrared reflection-absorption spectroscopy, (IRRAS) 18 For Peer Review Only 19 Measurement method [VIM 2.5] of spectroscopy based on reflection-absorption at 20 21 grazing incidence. 22 23 Note: RAIRS allows improved discrimination between species at the surface and 24 those in the bulk 25 26 637. remission function 27 28 29 See: Kubelka Munk function. 30 31 638. resonance Raman scattering, (RR) 32 33 Raman scattering that occurs through the polarizability of a molecule, (not the 34 35 hyperpolarizabilities) and is excited by electromagnetic radiation that is in resonance 36 with electronic transitions or vibronic transitions in the sample. 37 38 Source: [6]. 39 40 639. rotational branch 41 42 43 Spectral lines in the rotation-vibration spectrum of a gas that derive from the same 44 change in rotation quantum number, J. 45 46 Note 1: ∆J = Jupper – Jlower = –2, –1, 0, +1 and +2 for the O, P, Q, R and S branches, 47 respectively. 48 49 50 Note 2: The most commonly observed branches for simple molecules are the P, Q 51 and R branches in infrared spectroscopy and the O, Q and S branches in 52 Raman spectroscopy. 53 54 Source: [6]. 55 56 57 640. rotation-vibration spectrum 58 59 Spectrum which shows absorption or emission of radiation during transitions between 60 rotational-vibrational states of a molecule.

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1 2 3 Source: [6]. 4 5 6 641. scattering geometry 7 8 Relation between the propagation directions, ki, ks, and the polarization directions, pi, 9 ps, of the incident and scattered radiation, usually expressed in terms of laboratory- 10 fixed or crystal-fixed Cartesian axes. 11 12 13 Note: A common notation, due to Porto, is ki(pi ps)ks. 14 15 Source: [6]. 16 17 642. site splitting 18 For Peer Review Only 19 Appearance of more than one band in the spectrum of a crystal when only one is seen 20 21 in that of the gas, when this splitting is attributed to either the molecule lying on a 22 crystal site of lower symmetry than that of the gaseous molecule or to molecules 23 occupying more than one type of crystal site. See crystal field splitting. 24 25 Note: Site splitting arises from the static intermolecular forces in the crystal. 26 27 28 Source: [6]. 29 30 643. spatially offset Raman spectroscopy, (SORS) 31 32 Measurement method [VIM 2.5] of Raman spectroscopy in which the sample is 33 illuminated at one location, and the Raman signal is collected from a different location 34 35 on the sample surface. 36 37 Note: SORS allows chemical analysis of objects beneath diffusely scattering 38 surfaces, such as tissue, powders and translucent plastics. 39 40 644. spherical top 41 42 43 Molecule whose three principal moments of inertia are all the same. An isotropic 44 molecule. 45 46 Source: [6]. 47 48 645. Stark effect 49 50 51 Effect of an electric field on molecular energy levels and, hence, a spectrum. 52 53 Note: The spectral changes may be single lines splitting into multiplets, 54 frequencies shifts, inactive vibrations becoming active, or changed 55 intensities of active vibrations. 56 57 58 Source: [6]. 59 60

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1 2 3 646. step-scan interferometer 4 5 6 Interferometer (typically used for Fourier-transform infrared spectroscopy) in which 7 the optical path difference is changed by a certain amount, held constant, or modulated 8 if phase modulation is desired, while the signal at the current path difference is 9 recorded, then the process is repeated. 10 11 Source: [6]. 12 13 14 647. stimulated Raman scattering, (SRS) 15 16 Two-photon Raman scattering where a picosecond pump beam is used to create a 17 virtual state andFor a probe Peer beam of aReview frequency to match Only the frequency of Stokes Raman 18 scattering from the virtual state to a specific vibrational level. The Stokes emission is 19 stimulated thus depopulating the virtual state very quickly and increasing the scattering 20 21 efficiency for the chosen vibration by orders of magnitude. SRS is a non-linear process, 22 so sufficient photons from both the pump and probe beams must be present on the 23 molecule at the one time. 24 25 648. Stokes Raman scattering 26 Stokes scattering 27 28 29 Raman scattering of electromagnetic radiation in which the scattered radiation has 30 lesser energy (lesser wavenumber) than the exciting radiation. 31 32 Source: [6]. See also: anti-Stokes Raman scattering. 33 34 649. sum band 35 36 37 Band resulting from a sum transition. 38 39 Source: [6]. 40 41 650. sum transition 42 43 44 Combination transition between the ground state and a state in which more than one 45 vibration is excited; i.e., a transition from the ground state in which more than one 46 quantum number increases. 47 48 Source: [6]. 49 50 51 651. sum-frequency spectroscopy 52 53 Nonlinear optical technique in which pulsed lasers at frequencies ω1 and ω2 are 54 overlapped at a surface and light emitted at the sum of the two frequencies, ω1 + ω2, is 55 detected. One laser is normally in the mid-infrared and the other in the visible or near- 56 infrared. 57 58 59 Source: [6]. 60

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1 2 3 652. surface-enhanced hyper-Raman spectroscopy, (SEHRS) 4 5 6 Measurement method [VIM 2.5] of Raman spectroscopy by which the Raman spectrum 7 is significantly enhanced simultaneously by both the hyper-Raman (see: hyper-Raman 8 spectroscopy) and surface-enhanced Raman (see: surface-enhanced Raman 9 spectroscopy) effects. 10 11 Note: Very high enhancement factors of 1020 have been claimed. 12 13 14 653. surface-enhanced infrared absorption, (SEIRA) 15 16 Measurement method [VIM 2.5] of Raman spectroscopy by which the intensity of 17 absorption bandsFor of molecules Peer within Review a few nanometers Only of the surface of metal particles 18 is increased by interactions with surface plasmons (the collective resonance of electrons 19 near the surface of metal islands). 20 21 22 Note: The metals that give the largest enhancement are silver and gold, but this 23 phenomenon has been reported to occur with at least eight other metals. 24 25 Source: [6]. 26 27 28 654. surface-enhanced Raman spectroscopy, (SERS) 29 30 Measurement method [VIM 2.5] of Raman spectroscopy by which the intensity of 31 vibrational bands in the Raman spectra of molecules within a few nanometers of the 32 surface of microscopically rough metals, metal colloids and metal nanoparticles is 33 increased by several orders of magnitude. 34 35 36 Note 1: The metals that give the largest enhancement are silver, gold and copper, 37 but this phenomenon has been reported to occur with a range of other 38 metals. 39 40 Note 2: Other mechanisms of enhancement are known but the common usage of 41 SERS is with a metal or related systems and implies enhancement through 42 43 interaction with a surface plasmon. 44 45 Source: [6]. 46 47 655. surface-enhanced resonance Raman spectroscopy, (SERRS) 48 49 50 Measurement method [VIM 2.5] of surface-enhanced Raman spectroscopy (SERS) by 51 which the Raman spectrum is significantly enhanced when the conditions occur that 52 whilst undergoing SERS the molecules are excited by radiation that is in resonance 53 with electronic transitions in the sample. 54 55 Note: Enhancements of 1014 to 1015 have been measured. 56 57 58 59 60

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1 2 3 656. surface-enhanced, spatially offset Raman spectroscopy, (SESORS) 4 5 6 Measurement method [VIM 2.5] of Raman spectroscopy that combines spatially offset 7 Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS) enabling the 8 detection of a SERS signal deep within diffusely scattering samples. 9 10 657. symmetric (in vibrational spectroscopy) 11 12 13 Term used in at least two senses in vibrational spectroscopy. In general usage, a 14 symmetric molecule is a molecule with high symmetry. In more specific usage, a 15 property is symmetric with respect to a symmetry element if it remains unchanged by 16 the action of the corresponding symmetry operation. 17 For Peer Review Only 18 Source: [6]. 19 20 21 658. symmetric top 22 23 Molecule that has two equal principal moments of inertia with the third one different. 24 25 Source: [6]. 26 27 28 659. symmetry coordinate, S, Si 29 30 Each Si is a linear combination of general coordinates, usually internal coordinates, 31 constructed to take advantage of the molecular symmetry. The Si are elements of the 32 vector S. They have the same units as the general coordinates from which they were 33 constructed. 34 35 36 Source: [6]. 37 38 660. symmorphic space group 39 40 Space group that does not contain screw-axes and glide planes. 41 42 43 Source: [6]. 44 45 661. thermal diffusion depth, L, µs 46 thermal wave decay length 47 48 49 In photoacoustic spectroscopy, L = √(D/πf), where D is thermal diffusivity and f is 50 modulation frequency of the electromagnetic radiation. 51 52 Note 1: SI unit: m. Common unit: µm. 53 54 Note 2: 63% of the PAS signal originates within the thermal diffusion depth. 55 56 57 Source: [6]. 58 59 60

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1 2 3 662. thermal diffusivity, D, a 4 5 6 Thermal conductivity divided by the product of the specific heat and the density. 2 - 7 SI unit: m s 8 9 Source: [6]. 10 11 663. thermal wave decay coefficient, a 12 s 13 14 Reciprocal of the thermal diffusion depth (L). as = 1 / L. 15 16 SI unit: m-1. 17 For Peer Review Only 18 664. thermal wave decay length 19 20 21 See: thermal diffusion depth. 22 23 665. tip-enhanced Raman spectroscopy, (TERS) 24 25 Measurement method [VIM 2.5] of Raman spectroscopy combining surface-enhanced 26 Raman spectroscopy and scanning using an atomic force microscope or scanning 27 28 tunnelling microscope to give complementary maps of a surface. 29 30 See: [65]. 31 32 666. total internal reflection 33 34 35 Internal reflection from a non-absorbing material at angles of incidence at or above the 36 critical angle. 37 38 Source: [6]. 39 40 667. transflectance 41 42 43 Spectral intensity of a transflected beam divided by spectral intensity of the incident 44 beam in a transflection experiment. 45 46 Note: ‘Transflectance’ has also been used to mean transflection, and this usage is 47 strongly discouraged. 48 49 50 Source: [6]. 51 52 668. transflection 53 54 Reflection absorption at near-normal incidence when the thickness of the absorbing 55 medium is large enough to yield an interpretable spectrum. The substrate is usually a 56 57 mirror for mid-infrared measurements and a ceramic disk for near-infrared ° ° 58 measurements. The angle of incidence is typically between 0 and 45 . 59 60

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1 2 3 Note: Transflection is widely used in IR microscopy and is particularly 4 convenient for measuring transmission-like spectra in a near-infrared 5 6 instrument configured for diffuse reflection measurements by mounting the 7 sample on a non-absorbing diffusely reflecting substrate. 8 9 Source: [6]. 10 11 669. transmission Raman spectroscopy, (TRS) 12 13 14 Measurement method [VIM 2.5] of Raman spectroscopy in which the sample is 15 illuminated on one side and the Raman signal is collected from the opposite side. 16 17 Note: TRSFor allows Peer chemical analysisReview of objects Onlybeneath diffusely scattering 18 surfaces, e.g., within tissue, powders and pharmaceutical tablets or 19 capsules. 20 21 22 670. vibration mode 23 vibration 24 25 See: mode of vibration. 26 27 28 671. vibrational anharmonicity constant, ωexe, xrs, gtt’ 29 30 Constants in the vibrational term value. 31 32 Note: SI unit: m–1. Common unit: cm–1. 33 34 35 Source: [3] p25. See also: [6]. 36 37 672. vibrational circular dichroism, (VCD) 38 39 Circular dichroism, kL – kR, for vibrational transitions. 40 41 42 Note: Vibrations in chiral molecules and materials absorb left circularly polarized 43 radiation to a different extent than right circularly polarized radiation. 44 45 Source: [6]. 46 47 673. vibrational eigenvector, L, Lik 48 49 50 Part of the solution of the matrix equation of normal coordinate analysis, GFL=Lλ. 51 Each element Lik of L gives the change in internal coordinate Ri during unit change in 52 the normal coordinate Qk, as shown in matrix form by 53 54 R = LQ, i.e., L = ∂R /∂Q . 55 ik i k 56 57 Eigenvectors are sometimes expressed in terms of symmetry coordinates or Cartesian 58 coordinates. 59 60 SI unit: kg–1/2; Common unit: u–1/2 = 2.45400 × 1013 kg–1/2.

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1 2 3 Source: [6]. 4 5 6 674. vibrational kinetic energy, T 7 8 Kinetic energy of the molecule as a function of the displacements of the atoms from 9 equilibrium positions. For Cartesian displacement coordinates, x, y, z 10 2 2 2 � = ∑ ½��(� + �� + ��) , where the sum is over all atoms and �� , etc., are the 11 � � � � ―1 12 displacement velocities. For internal coordinates � = ½� �� = ½� � � = ½ 13 ∑ ―1 � t �� where � and � are the row and column vector, respectively, of the ∂Ri/∂t, 14 t 15 P and P are the row and column vector, respectively, of the momenta conjugate to the –1 ―1 th –1 16 Ri, G is the inverse of the G matrix and �� is the ij element of G . The elements 1 17 th th of the G matrix are defined by �� = ∑ ��where Biα and Bjα relate the i and j 18 For Peer Review�� Only th 19 internal coordinate to the α Cartesian coordinate through the equation R = BX in 20 which X is the column vector of the Cartesian coordinates. 21 22 Note: SI unit: J 23 24 25 Source: [6]. 26 27 675. vibrational potential energy, V 28 29 Potential energy of the molecule as a function of the displacements of the atoms from 30 equilibrium positions. The harmonic terms are quadratic in the displacements and the 31 anharmonic terms are of cubic, quartic and higher orders in the displacements. 32 33 In terms of normal coordinates 34 35 2 2V = ∑λkQk + ∑ kijkQiQjQk + higher terms 36 k ijk 37 In terms of internal coordinates, 38 39 40 2 2V = ∑ Fii Ri + ∑ Fij Ri Rj + ∑ Fijk Ri Rj Rk + higher terms 41 i i, j≠i i, j,k . 42 SI unit: J 43 44 45 Source: [6]. 46 47 676. vibrational spectroscopy 48 49 Measurement principle [VIM 2.4] of spectroscopy to analyse molecular properties 50 51 based on vibrations (bond stretching or deformation modes) in chemical species. 52 53 Note: Typically vibrational spectroscopy uses the low energy end of the visible 54 spectrum i.e. infrared or near infrared. 55 56 677. vibrational term value, G 57 58 59 Vibrational energy, E, expressed in wavenumber units. G = E/(hco), where h is the 60 Planck constant and c0 is the speed of light in vacuum.

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1 2 3 Note 1: G is usually written with zero-energy at the minimum of the potential 4 energy curve for a diatomic molecule as: 5 2 3 6 G = ωe (v +1/ 2) −ωe xe (v +1/ 2) +ωe ye (v +1/ 2) + higher terms, and for a 7 polyatomic molecule G = ω (v + d / 2) + X (v + d / 2)(v + d / 2) + 8 ∑ k k k ∑ ij i i j j k i≤ j 9 10 higher terms, where v, vk, etc. = 0, 1, 2, 3,··· , and d is the degeneracy of a 11 vibration. Xij are the anharmonic constants. 12 13 Note 2: SI unit: m–1, Common unit: cm–1. 14 15 Source: [6]. 16 17 18 678. vibronicFor transition Peer Review Only 19 20 Transition that changes the electronic and vibrational state of the molecule 21 22 679. volume reflection 23 24 Kubelka Munk reflection 25 deprecated: diffuse reflection 26 27 Re-emergence of electromagnetic radiation from the surface of incidence after 28 penetrating into a powdered sample. 29 30 Source: [6]. 31 32 33 680. wavenumber shift, ∆� 34 35 See Raman wavenumber shift. 36 37 INDEX OF SYMBOLS AND ABBREVIATIONS 38 39 40 α absorptance 41 α polarizability 42 αi internal absorptance 43 � (�) local molar polarizability 44 � 45 β hyperpolarizability 46 γ gyromagnetic ratio 47 Γ full width at half height 48 δ chemical shift in NMR 49 50 �� spectral resolution at frequency � 51 δ� spectral resolution at wavenumber � 52 δλ spectral resolution at wavelength λ 53 ∆E energy change of an electromagnetic transition 54 55 ∆� Raman wavenumber shift 56 ∆� free spectral range 57 ∆t natural lifetime of an excited state 58 ε emittance 59 ε energy level of ith state (See: Boltzmann distribution of nuclear spins) 60 i

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1 2 3 � relative permittivity 4 5 η nuclear Overhauser effect 6 θ angle of incidence 7 θc critical angle 8 θ E Ernst angle 9 Θ molar ellipticity 10 11 κ attenuation index (See: complex refractive index) 12 λ wavelength in medium 13 λ0 wavelength in vacuum 14 µ electric dipole moment 15 µ optical absorption depth 16 β 17 µs Forscattering Peer coefficient Review Only 18 µs thermal diffusion depth 19 ν frequency 20 � wavenumber 21 peak wavenumber 22 �0 23 ρ depolarization ratio 24 ρ radiant energy density 25 ρ ṽ , ρλ spectral radiant energy density 26 27 σ wavenumber in medium 28 τ transmittance 29 τ, τc correlation time 30 τd dwell time 31 τ internal transmittance 32 i 33 ϕ0 received radiant flux density 34 ϕr(λ) reference flux density 35 ϕs(λ) sample flux density 36 φN noise equivalent power (See: noise) 37 ϕT(λ) solvent blank flux density 38 Φ radiant power 39 40 ψ ellipticity 41 ω, ω L Larmor frequency 42 ωe, ωk harmonic constant 43 ωexe vibrational anharmonicity constant 44 45 46 a thermal diffusivity 47 as thermal wave decay coefficient 48 A absorbance 49 A10 experimental absorbance 50 A10, A decadic absorbance 51 Ai internal absorbance 52 B radiofrequency magnetic flux density (See: adiabatic pulse) 53 54 B0 static magnetic flux density 55 c amount-of-substance concentration 56 c speed of electromagnetic radiation 57 cBE background equivalent concentration 58 d depth of penetration in attenuated total reflection 59 p 60 D thermal diffusivity

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1 2 3 E received radiant flux density 4 E intensity of radiation 5 ṽ 6 eQ nuclear electric quadrupole moment 7 f frequency 8 fNyquist Nyquist frequency 9 fSW NMR spectral width 10 F fluence 11 g degeneracy 12 g vibrational anharmonicity constant 13 tt’ 14 G optical throughput of a spectrometer 15 G vibrational term value 16 h Planck constant (See: electromagnetic radiation) 17 H fluence 18 For Peer Review Only HG peak height (band maximum) (See: Gaussian band, Lorentzian band) 19 I intensity of radiation 20 21 I received radiant flux density 22 I0 incident intensity of radiation 23 Iṽ spectral intensity 24 Ie radiant intensity 25 Is intensity of radiation scattered (See: scattering coefficient) 26 J rotation quantum number (See: rotational branch) 27 J spin-spin coupling constant 28 29 k absorption index 30 l path-length 31 L radiance 32 L thermal diffusion depth 33 L, Lik vibrational eigenvector 34 L , L spectral radiance 35 ṽ λ 36 M radiant excitance 37 � complex refractive index 38 p electric dipole moment 39 P radiant power 40 P0 incident radiant power (See: absorptance, diffuse reflectance) 41 Pabs absorbed radiant power (See: absorptance) 42 P remitted radiant power (See: diffuse reflectance) 43 rem 44 Qk normal coordinate 45 R remittance (See: diffuse reflectance) 46 R resolving power 47 RS/N signal-to-noise ratio 48 s scattering coefficient 49 S, S symmetry coordinate 50 i 51 Sn improper rotation axis 52 taq acquisition time 53 T2 spin-lattice relaxation time 54 T2* net dephasing time 55 T transmittance 56 T vibrational kinetic energy 57 T echo time 58 E 59 Ti internal transmittance 60 TI inversion time

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1 2 3 Tr repetition time 4 V vibrational potential energy 5 6 Vm molar volume (See: local molar polarizability) 7 w radiant energy density 8 W full width at half height 9 xrs vibrational anharmonicity constant 10 11 AAS atomic absorption spectroscopy 12 AES atomic emission spectroscopy 13 14 AES Auger electron spectroscopy 15 AFS atomic fluorescence spectroscopy 16 AMTIR amorphous material transmitting infrared radiation 17 APT Foratomic polarPeer tensor Review Only 18 AT acquisition time 19 ATR attenuated total reflection 20 21 CAMELPSIN cross-relaxation appropriate for minimolecules emulated by locked 22 spins (See: rotating-frame NOE spectroscopy) 23 CARS coherent anti-Stokes Raman spectroscopy 24 CCD charge coupled device 25 CD circular dichroism 26 COLOC correlation spectroscopy through long-range coupling 27 COSY correlation spectroscopy 28 29 CP/MAS cross polarisation with magic angle spinning NMR 30 CRAMPS combined rotation and multiple pulse spectroscopy 31 CSA chemical shift anisotropy 32 CW continuous wave (See: Fourier-transform spectroscopy) 33 DC direct current. (See: radiofrequency glow discharge optical emission 34 spectroscopy, direct current glow discharge optical emission 35 spectroscopy) 36 37 DC GD-OESdirect current glow discharge optical emission spectroscopy 38 DEPT distortionless enhancement by polarisation transfer 39 DIPSI decoupling in the presence of scalar interactions 40 DOSY diffusion ordered spectroscopy 41 DPFGSE double pulsed-field gradient spin-echo excitation 42 DQF-COSY double-quantum filtered correlation spectroscopy 43 44 ECCF equilibrium charge, charge flux (See: electro-optic parameter) 45 EELS electron energy loss spectroscopy 46 EM electromagnetic radiation 47 EOP electro-optic parameter 48 ERETIC electronic reference to access in vivo concentrations 49 ESCA electron spectroscopy for chemical analysis (See: X-ray photoelectron 50 spectroscopy) 51 52 ETAAS electrothermal atomic absorption spectroscopy 53 EXSY exchange spectroscopy 54 FFC-NMR fast field cycling NMR relaxometry 55 FID free induction decay 56 FMIR frustrated internal reflection spectroscopy (See: multiple attenuated total 57 reflection) 58 FT-IR Fourier transform infrared (See: Fourier-transform infrared spectroscopy) 59 60 FWHH full width at half height (See: full width at half maximum)

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1 2 3 FWHM full width at half maximum 4 GARP globally optimized alternating-phase rectangular pulses 5 6 GD-OES glow discharge optical emission spectroscopy 7 H2BC heteronuclear multiple-bond correlation over two bonds 8 HETCOR heteronuclear shift correlation NMR 9 HMBC heteronuclear multiple bond correlation 10 HMQC heteronuclear multiple-quantum correlation NMR 11 HMQC-TOCSY heteronuclear multiple-quantum correlation with additional TOCSY 12 transfer 13 14 HOESY heteronuclear Overhauser effect spectroscopy 15 HOHAHA homonuclear Hartmann-Hahn spectroscopy (See: total correlation 16 spectroscopy) 17 HREELS Forhigh resolution Peer electron Review energy loss spectroscopy Only 18 HRS hyper-Raman spectroscopy 19 HSQC heteronuclear single quantum correlation 20 21 HSQMBC heteronuclear single quantum multiple-bond correlation 22 HSQC-TOCSY heteronuclear single quantum correlation with additional TOCSY 23 transfer 24 HWHH half width at half height (See: half width at half maximum) 25 HWHM half width at half maximum 26 ICCD intensified charge coupled device detector 27 ICP inductively-coupled plasma 28 29 ICP-MS inductively-coupled plasma mass spectrometry 30 ICP-OES inductively-coupled plasma optical emission spectroscopy 31 IETS inelastic electron tunnelling spectroscopy 32 INADEQUATE incredible natural-abundance double-quantum transfer 33 experiment 34 INEPT insensitive nuclei enhanced by polarization transfer 35 ILS instrument line shape 36 37 IR infrared (See: infrared radiation) 38 IRS internal reflection spectroscopy (See: attenuated total reflection 39 spectroscopy) 40 IRRAS infrared reflection-absorption spectroscopy (See: reflection-absorption 41 infrared spectroscopy) 42 J-MOD J-modulated spin-echo 43 44 J-RES J-resolved spin-echo 45 LIBS laser-induced breakdown spectroscopy 46 LTE local thermal equilibrium (See: plasma local thermodynamic equilibrium) 47 MATR multiple attenuated total reflection 48 MCP microchannel plate (See: intensified charge coupled device detector) 49 MIR multiple internal reflection (See: multiple attenuated total reflection) 50 MQMAS multiple-quantum magic angle spinning NMR 51 52 NA numerical aperture 53 NMR nuclear magnetic resonance (See: nuclear magnetic resonance 54 spectroscopy) 55 NMRR nuclear magnetic resonance relaxometry 56 nOe, NOE nuclear Overhauser effect 57 NOESY nuclear Overhauser effect spectroscopy 58 NQR nuclear quadrupole resonance (See: nuclear quadrupole resonance 59 60 spectroscopy)

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1 2 3 NUS non-uniform sampling 4 OES optical emission spectroscopy 5 6 OMTS orbital mediated tunnelling spectroscopy 7 OPD optical path difference 8 ORD optical rotatory dispersion 9 PAS photoacoustic spectroscopy 10 PFG pulsed-field gradient 11 PSYCHE pure shift yielded by chirp excitation 12 QCL quantum cascade laser 13 14 RAIRS reflection-absorption infrared spectroscopy 15 RDC residual dipolar coupling 16 REDOR rotational echo double resonance 17 RFFor radiofrequency Peer Review Only 18 RF-GD-OESradiofrequency glow discharge optical emission spectroscopy 19 RIXS resonant inelastic X-ray scattering 20 21 ROA Raman optical activity 22 ROESY rotating-frame NOE spectroscopy 23 RR resonance Raman (See: resonance Raman scattering) 24 SE spin echo 25 SEHRS surface-enhanced hyper-Raman spectroscopy 26 SERRS surface-enhanced resonance Raman spectroscopy 27 SERS surface-enhanced Raman spectroscopy 28 29 SESORS surface-enhanced, spatially offset Raman spectroscopy 30 SIERA surface-enhanced infrared absorption 31 S/N signal-to-noise ratio 32 SNR signal-to-noise ratio 33 SNRdB signal-to-noise ratio measured in decibel 34 SORS spatially offset Raman spectroscopy 35 SRS stimulated Raman spectroscopy 36 37 SSNMR solid-state nuclear magnetic resonance spectroscopy 38 STD saturation transfer difference spectroscopy 39 T2-star net dephasing time 40 TD-NMR time domain nuclear magnetic resonance spectroscopy 41 TE echo time 42 TERS tip-enhanced Raman spectroscopy 43 44 TI inversion time 45 TM transverse magnetic (See: p-polarization). 46 TOCSY total correlation spectroscopy 47 TOSS total suppression of spinning sidebands 48 TR repetition time 49 TROSY transverse relaxation optimized spectroscopy 50 TRS transmission Raman spectroscopy 51 52 VCD vibrational circular dichroism 53 VEELS vibrational electron energy loss spectroscopy (See: high resolution 54 electron energy loss spectroscopy) 55 XAES X-ray excited Auger electron spectroscopy 56 XPS X-ray photoelectron spectroscopy 57 58 59 60

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1 2 3 ACKNOWLEDGMENTS 4 5 6 Many of the terms listed within the General Section and the section on molecular 7 spectroscopy, in particular those associated with vibrational spectroscopy, are based on 8 a Glossary of Terms compiled by John Bertie1. Additional input and up-dates have been 9 compiled by John Chalmers and Geoffrey Dent, on behalf the UK Infrared and Raman 10 Discussion Group (IRDG)2. 11 12 13 MEMBERSHIP OF SPONSORING BODIES 14 15 The membership of Division V (Analytical) at the start of this project was 16 17 President: D.For B. Hibbert; Peer Vice-President: Review J. Labuda; Secretary:Only Z. Mester; Past 18 President: M. F. Camões; 19 20 21 Titular Members: C. Balarew, Y. Chen; A. Felinger, H. Kim, M. C. Magalhães, H 22 Sirén; Associate Members: R. Apak, P. Bode, D. Craston, Y. H. Lee, T. Maryutina, N. 23 Torto; National Representatives: O. C. Othman, L. Charles, P. DeBièvre, M. Eberlin, 24 A. Fajgelj, K Grudpan, J. Hanif, D. Mandler, P. Novak, and D. Shaw. 25 26 27 28 29 The present membership of Division V is 30 31 President: Zoltan Mester; Pat President: Jan Labuda; Vice President: Érico Marlon de 32 Moraes Flores; Secretary: Takae Takeuchi; 33 34 Titular Members: Medhat A. Al-Ghobashy, Derek Craston, Attila Felinger, Irene 35 36 Rodriguez Meizoso, Sandra Rondinini, David Shaw. Associate Members: Jiri Barek, 37 M. Filomena Camões, Petra Krystek, Hasuck Kim, Ilya Kuselman, M. Clara 38 Magalhães, Tatiana A. Maryutina; National Representatives: Boguslaw Buszewski, 39 Mustafa Culha, D. Brynn Hibbert, Hongmei Li, Wandee Luesaiwong, Serigne Amadou 40 Ndiaye, Mariela Pistón Pedreira, Frank Vanhaecke, Winfield Earle Waghorne, Susanne 41 Kristina Wiedmer 42 43 44 45 46 47 48 49 50 51 1 John Bertie, with the help of John Chalmers and Peter Griffiths for the Glossary of Terms used in Vibrational 52 Spectroscopy for the Handbook of Vibrational Spectroscopy, Vol. 5., pp.3745-3793, edited by J.M Chalmers 53 and P.R. Griffiths, published by John Wiley & Sons Ltd., Chichester ©2002. Help and advice on specific topics 54 for this were given by: Colin Bain, Don Dahm, Bonner Denton, Neil Everall, Kerry Hipps, Richard 55 Jackson, Glen Loppnow, Howard Mark, Robin McDowell, Jeanne McHale, Kirk Michaelian, Larry 56 Nafie, Isao Noda, Andre Sommer, and Gwyn Williams. 57 58 2 IRDG members, in particular Karen Faulds, Duncan Graham, Neil Everall, Pavel Matousek, and Ewen Smith, 59 contributed in these inputs and additions. 60

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