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The Acetylene Ground State Saga Michel Herman The acetylene ground state saga Michel Herman To cite this version: Michel Herman. The acetylene ground state saga. Molecular Physics, Taylor & Francis, 2008, 105 (17-18), pp.2217-2241. 10.1080/00268970701518103. hal-00513123 HAL Id: hal-00513123 https://hal.archives-ouvertes.fr/hal-00513123 Submitted on 1 Sep 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Molecular Physics For Peer Review Only The acetylene ground state saga Journal: Molecular Physics Manuscript ID: TMPH-2007-0155 Manuscript Type: Invited Article Date Submitted by the 30-May-2007 Author: Complete List of Authors: Herman, Michel; Université Libre de Bruxelles, Chimie quantique et Photophysique acetylene, global picture, high resolution spectroscopy, Keywords: instrumental developments, intramolecular dynamics URL: http://mc.manuscriptcentral.com/tandf/tmph Page 1 of 93 Molecular Physics 1 2 3 4 11 July 2010 5 Invited Manuscript 6 7 8 9 10 The acetylene ground state saga 11 12 13 14 15 Michel HERMAN 16 ServiceFor de PeerChimie quantique Review et Photophysique, Only CP 160/09 17 18 Université libre de Bruxelles (U.L.B.) 19 Ave. Roosevelt, 50. 20 21 B-1050 22 Brussels 23 24 Belgium 25 26 27 [email protected] 28 29 30 Pages : 57 31 32 Figures : 32 (including 2 colour figures) 33 Tables : 3 34 35 36 This ms was written using ‘‘century schoolbook’’ and, whenever necessary, 37 38 ‘‘symbol’’ fonts. A careful distinction was made between italic vee’s and 39 Greek nu’s both in the text and in formulas, that is important to respect. It 40 41 will only be visible if using ‘‘century schoolbook’’ as the major font to 42 visualize and print the text. 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 1 URL: http://mc.manuscriptcentral.com/tandf/tmph Molecular Physics Page 2 of 93 1 2 3 4 Abstract 5 6 7 8 The evolution of the high-resolution spectroscopic investigation of the 9 10 11 vibration-rotation energy states of acetylene in its ground electronic state 12 13 is presented, with focus on advances co-authored by the ULB group. The 14 15 16 emergenceFor of a global Peer picture Reviewaccounting for all Only available spectroscopic 17 18 fingerprints, at their full accuracy, is highlighted. Contribution of this 19 20 21 research to various topics is illustrated, including instrumental 22 23 developments, local mode trends, quantum vs . classical correspondence, 24 25 26 energy vs . time approaches and nucleation processes. 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 2 URL: http://mc.manuscriptcentral.com/tandf/tmph Page 3 of 93 Molecular Physics 1 2 3 1. Introduction 4 5 6 7 8 9 As reported by Miller in a book dedicated to acetylene [1], Edmund Davy 10 11 told the 1836 meeting of the British Association at Bristol that [2] 12 13 14 15 16 ‘‘in attemptingFor to Peerprocure potassium Review by strongly Only heating a mixture of 17 18 calcined tartar and charcoal in a large iron bottle, I obtained a black 19 20 21 substance which readily decomposed water and yielded a gas which proved 22 23 to be a new compound of carbon and hydrogen. This gas burns in air with 24 25 26 a bright flame, denser and of greater splendour than even olefiant gas...In 27 28 contact with chlorine, instant explosion takes place, accompanied by a 29 30 31 large red flame and the deposition of much carbon…The new gas requires 32 33 for its complete combustion 2,5 volumes of oxygen gas, which are converted 34 35 36 into two volumes of carbonic acid and water, which are the only products of 37 38 its combustion... It is admirably adapted for the purposes of artificial light 39 40 41 if it can be procured at a cheap rate’’ 42 43 44 45 46 Edmund Davy identified this new gas as a "new (bi)carburet of hydrogen". 47 48 It was rediscovered in 1860 by French chemist Marcellin Berthelot, who 49 50 51 coined the name "acétylène." 52 53 54 55 56 As stated in an encyclopaedia: Acetylene (systematic name: ethyne) is 57 58 the simplest alkyne hydrocarbon, consisting of two hydrogen atoms and two 59 60 carbon atoms. Because it contains a triple bond, acetylene is an 3 URL: http://mc.manuscriptcentral.com/tandf/tmph Molecular Physics Page 4 of 93 1 2 3 unsaturated chemical compound. The carbon-carbon triple bond leaves the 4 5 6 carbon atoms with two sp hybrid orbitals for sigma bonding, placing all 7 8 four atoms in the same straight line, with CCH bond angles of 180°. 9 10 11 Acetylene indeed provides the simplest example of carbon-carbon 12 13 triple bond and, as such, is referenced for its prototype geometrical 14 15 16 structure Forin textbooks, Peer with CH Review and CC bonds claimed Only to be 120 and 106 17 18 pm long. The latest equilibrium ( r ) and ground ( r ) internuclear distances 19 e 0 20 21 in acetylene, from [3], are, in pm: 22 23 24 25 26 rCH( )= 106.138(35); rCC ( ) = 120.292(13) e e (pm). 27 ( ) 105.756(52); ( ) 120.830(20) 28 rCH0 = rCC0 = 29 30 31 32 33 As such, they provide the most accurate values today available for the 34 35 basic CC triple bond and related CH distances. Interesting enough, these 36 37 38 bond lengths have not been optimally determined yet [4]. In addition, the 39 40 linear geometry refers to the ground electronic state and not to the first 41 42 43 and some additional excited electronic states. 44 45 46 47 48 The importance of acetylene in the ‘‘real world’’ dealt with in 49 50 encyclopaedias arises mainly from its application in synthetic organic 51 52 53 chemistry. Numerous prototype reaction mechanisms are well known and 54 55 of daily use to academic and industrial chemists . 56 57 58 Even in such ‘‘ordinary’’ chemistry, however, the detailed reaction 59 60 path may involve geometrical isomers of acetylene, such as vinylidene, a 4 URL: http://mc.manuscriptcentral.com/tandf/tmph Page 5 of 93 Molecular Physics 1 2 3 still evanescent species apparently resisting definite experimental 4 5 6 evidence. Furthermore, acetylene is present on Earth and in various other 7 8 planetary and also in stellar atmospheres, as well as in the interstellar 9 10 11 medium. As such, it is also a key species in astrochemistry. However, 12 13 related reaction mechanisms can often hardly be unravelled by textbook 14 15 16 knowledgeFor in organic Peer chemistry Review given the most Only specific experimental 17 18 conditions ruling astrochemistry. Acetylene chemistry is thus far from 19 20 21 mastered. Figure 1 presents previously unpublished spectra from the 22 23 Atmospheric Chemistry Experiment (ACE) mission demonstrating the 24 25 26 presence of acetylene in the Earth atmosphere. 27 28 29 30 31 Insert figure 1 32 33 34 35 36 37 38 Pure acetylene is a colourless, highly flammable gas with an 39 40 41 agreeable ethereal (ether-like) odour but the odour of the commercial purity 42 43 grade is distinctively garlic-like. 44 45 46 Reference to acetylene as a single species is misleading since for the 47 48 symmetric isotopologues, including 12 C H , there are two nuclear spin 49 2 2 50 51 isomers, ortho and para that seem not to interconvert easily, if they can 52 53 ever be forced to do so one day. One should therefore rather mention two 54 55 56 independent, coexisting acetylene molecules, each long lived and with 57 58 close but distinct thermodynamical properties, possibly specific chemistry 59 60 and, who knows, different smells? The lack of the expected 1:3, para :ortho 5 URL: http://mc.manuscriptcentral.com/tandf/tmph Molecular Physics Page 6 of 93 1 2 3 intensity alternation in the ν fundamental vibration-rotation band in 4 3 5 12 6 C2H2 observed in the spectrum of figure 2, at specific J-values is typically 7 8 9 the observation that ‘‘spin-diggers’’ are searching for. It turns out, 10 11 however, that this peculiar observation is rather to be attributed to a 12 13 14 succession of emission-absorption schemes, thus not requiring any spin 15 16 conversionFor process, Peer as correctly Reviewinterpreted at the Onlytime. 17 18 19 20 21 Insert figure 2 22 23 24 25 26 27 28 29 30 31 Because, acetylene is important and stable, it is a very well known 32 33 34 chemical object, with numerous well documented properties in organic and 35 36 physical chemistry. Because acetylene is light and simple, it is an ideal 37 38 39 target to produce high quality spectroscopic data and elaborate quantum 40 41 models. Furthermore, with 7 vibrational degrees of freedom including two 42 43 44 doubly degenerate ones, acetylene supports complex intramolecular 45 46 mechanisms of direct relevance to the understanding of larger species.
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