Infrared Spectroscopy of Molecules in the Gas Phase

Infrared Spectroscopy of Molecules in the Gas Phase Keqing Zhang A t hesis presented to the University of Waterloo in fdflment of the thesis requirement for the degree of Doctor of Philosophy in Chemistry Waterloo, Ontario, Canada. 1997 @Keqing Zhang 1997 Nationai Library Bibliothèque nationaie du Canada Acqui..itions and Acquisitions et Bibliographie Senrices services bibliographiques The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National LiIbrary of Canada to Bibliothèque nationale du Canada de reproduce, loan, distn'biite or sell reproduire, prêter, distriiuer ou copies of Mer thesis by any means vendre des copies de sa thèse de and in any form or format, making quelque dèreet sous queIque this thesis available to interested forme que ce soit pour mettre des pemns. exemplaires de cette thèse à la disposition des personnes intéressées. The author retains omership of the L'auteur conserve la propriété du copyright in Merthesis. Neither droit d'auieur qui protège sa thése. Ni the thesis nor substantiai extracts ia thèse ni des extraits substantiels de fkom it may be printed or otherwise celle-ci ne doivent être miprimés ou reproduced with the author's autrement reproduits sans son permission. autorisation. The University of Waterloo requires the signatures of all persons using or ph* tocopying this thesis. Please sign below, and give address and date. Abstract Fourier transforxn idiared spectroscopy is appiied to the studies of several very different moledar systems. The spectra of the diatomic moledes BF, ALF, and MgF were recorded and analyzed. Ddamcoefficients wae obtained. The data of two isotopomers, "BF and l0BF, were used to determine the mas-reduced Dunham coefficients, dong with Born-Oppenheimer breakdom constants. Parameterized potential energy functions of BF and ALF were determined by fitting the adable data using the soluti~nsof the radiai Schr6dinge.r equation. Two vibrational modes of the short-lived and reactive BrCNO molecule were recorded at high resolntion. Rotation-vibration transitions of the fundamental bands of both isotopomers "BrCNO and "BrCNO were assigned and analyzed. From the rotational constants, it was found that the Br-C bond length in BrCNO anomalously short when a linear geometry was assnmed. This may indicate that Br CNO is quasi-linear , simulating the parent HCNO molecule. The emission spectra of the gaseous polycyclic aromatic hydrocarbon (PAH) moledes napht halene, ant hracene, pyrene, and ehrysene were recorded in the far- infiared and mid-infkared regions. The assignments of fundamental modes and some combination modes were made. The vibrational bands that lie in the far- infrared are unique for different PAHs and dow diserimination among the four PAH moledes. The far-i&ared PAH spectra, therefore, may prove useful in the assignments of auidentified spectral features kom astronomical objects. Acknowledgements 1 would like to extend rny thanks to my supervisor Dr. Peter Bernath for his suentific inspiration, patience, and constant encouragement throughout the course of this research. It was a great pleasure to work with Dr. Bujin Guo on many projects. 1 would also like to thank Dr. Nick Westwood and Dr. Tibor Pasinszki for providing expertise and helping to set up the experiments on nitrile oxides. Finally, 1 would like thank Pina Colanisso, Zulf Morbi and Chdeng Zhao for th& collaboration and enlightenment. For my deSue and my mother and father Contents A bst ract Adcnowledgements Table of Contents vii List of Figures List of Tables 1 Introduction 1 1.1 Absorption vs. Ernission Infiared Spectroscopy ............ 5 1.2 Diatomic Molecules ........................... 6 1.3 Polyatomic Molecales .......................... 9 2 Fourier Tkansform Idkared Spectroscopy 12 2.1 TheMichelsonInterferorneter ..................... 13 2.2 Advantages of Fourier Transform Spectroscopy ............ 16 2.3 The Bder Spectrometer ....................... 19 3 Infiared Spectroscopy of Diatomic Molecules 22 3.1 The Born-Oppenheimer Approximation ................ 23 3.2 Born-Oppenheimer Breakciown .................... 27 3.3 The Dunham Potential Model ..................... 28 3.4 The Parameterized Potential Mode1 .................. 34 3.5 Mared Emission Spectroscopy of BF and AU? ............ 38 3.5.1 Experiment ........................... 39 3.5.2 Results and Discussion ..................... 43 3.5.3 Conclusion ........................... 52 3.6 kifrared Emission Spectroscopy of MgF ................ 54 3.6.1 Experiment ........................... 55 3.6.2 Results .............................. 56 4 High Resolution Infhred Spectroscopy of Nitrile Oxides 60 4.1 Experiment ............................... 62 4.2 Resdts and Analysis .......................... 65 4.3 Conclusion ................................ 72 5 Vibrational Spectroscopy of Polycydic Aromatic Hydrocarbon Molecules 74 5.1 Classical Mechanical Tkeatment of MoIecular Vibration ....... 75 5.2 Quantum Mechanical Tkeatment of Molecular Vibration ....... 78 5.3 Group Fiequenues ........................... 80 5.4 Selection Rdes for Normal Modes of Vibration ............ 81 5.5 Polycydic Aromatic Hydrocarbon Moledes in Astronomy ..... 83 5.6 Laboratory Infrared Experiments on PAHs .............. 87 5.7 Results.. -.. 89 5.7.1 Far-infrared Region . - 90 5.7.2 Mid-infrared Region . 95 References A BF Line Positions B MgF Line Positions C BrCNO Line Positions List of Figures The schematic of the Michelson interferorneter ............ 14 The optical layout of the Bde~IFS 120 HR Fouria transform spectrometer ................................. 21 The schematic of CM Rapid Temp furnace .............. 41 Kigh resolution emission spectnun of BF ............... 42 The Born-Oppenheimer potential energy hinction for BE' ...... 49 High resolution emission spectm of MgF .............. 57 Setup for the BrCNO absorption experiment ............. 64 The overview of the high resolution spectrum of BrCNO ut band . 67 The expanded view of BrCNO zq band R branch ........... 68 Far-infrared emission spectra of naphthalene ............. 91 Far-infrared emission spectra of anthracene .............. 92 Far-infrared emission spectra of pyrene ................ 93 Far-infrared emission spectra of chrysene ............... 94 Mid-infrared emission spectra of pyrene ................ 96 List of Tables 3.1 Dunham coefficients for BF ...................... 45 3.2 Mas-reduced Dunham coefficients for BF .............. 46 3.3 InternudearpotentialenergyparmetersforBF ........... 48 3.4 Dunham coefficients for AlF ...................... 50 3.5 Internuclear potential energy parameters for AlF ........... 51 3.6 Relative transition dipole moments of "BF .............. 53 3.7 Dunham coefficients for MgF ...................... 59 4.1 The spectroscopic constants of BrCNO ................ 69 4.2 The bondlengthsin BrCNO ...................... 71 4.3 Theoretical structure of BrCNO .................... 73 5.1 Vibrational fiequenaes and intensities of naphthalene ........ 97 5.2 Vibrational frequencies and intensities of anthracene ......... 99 5.3 Vibrational fiequencies and intensities of pyrene ........... 101 5.4 Vibrational hequenues and intensities of chrysene .......... 104 5.5 Requencies of combination bands of PAHs .............. 108 5.6 Observed band positions of PAHs ................... 112 A .1 O bserved line positions of BF ...................... 129 B .1 O bserved line positions of MgF ..................... 138 C.l Observed line positions of "BrCNO .................. 147 C.2 Observed line positions of 'IBrCNO .................. 153 Chapter 1 Introduction Molecular spectroscopy is a branch of science in which the interactions of electromagnetic radiation and matter are studied. The aims of these stndies are to elucidate information on moledar strnctnre and dynamics, the environment of the sample molecules and their state of association, interactions witL solvents. and many nther topics. The resuits fiom spectroscopy have, therefore, played an im- portant role in many disciplines of science, induding biochemistry [l], environ- mental research [21, chernical dynamics [3], astrophysics [4,5], and atmospheric diemistry [6,7]. The interaction of the radiation with the moledes is nsually expressed in terms of a resonance condition, which implies that th energy clifference between two stationary states in a molede must be matched exactly by the energy of the where h is the Planck constant, c is the speed of light in vacuum, v is fiequency and O is the wavenumber which has the unit mi". This view of the interaction between light and matta is, however, rather cursory, since radiation interacts with matter even when its wavelength is different from the specific wavelength at which a resonance occurs. These off-resonsnce interactions bet ween electromagnetic radiation and matter give rise to well-hown phenornena such as the Raman dect [BI. The interactions between moledes and photons determine the intensit ies, widt hs, and shifts of spectral lines and the intensity and spectral distribution of continuous radiation [9]. Molecular spectroscopy is nsudy dassified by the wavelength range of the electromagnetic radiation, for example, idkared spectroscopy and microwave spectroscopy. This dissertation mainly covers some aspects of infrared spectroscopy. Although vibration-rotation transitions in the infirarecl are relatively weak (101, when compared with electronic transitions, aU molecules except hornonuclear di- atonie

Load more