title: Are asymmetric stretch Raman spectra by centrosymmetric molecules depolarized?: the 2ν3 overtone of CO2.
abstract: Molecular vibrations that are not totally symmetrical give rise to depolarized lines [P. Atkins and J. de Paula, Atkins' Physical Chemistry (Oxford University Press, UK, 2006), p. 464]. But in the case of stretching vibrations in centrosymmetric molecules, the statement has so far not been conclusively verified. It is the purpose of this article to report a rigorous experimental and theoretical analysis of the 2ν(3) band of CO(2)--the first overtone of the asymmetrical stretch vibration. The anisotropic spectrum was extracted and its spectral moment calculated from light-scattering measurements, taken at room temperature and for a wide range of CO(2)-gas densities. Evidence for a near-entirely depolarized Raman band is provided, with integrated depolarization ratio η(int)=6/7.16, closely approaching the upper bound η(max)=6/7. Agreement with theoretical predictions is found, on the basis of quality ab initio data for polarizability properties, provided that electro-optical and mechanical anharmonicity and intermode coupling effects between symmetric ν(1) and antisymmetric ν(3) stretching vibrations are incorporated.
authors.affiliation: MolTech-Anjou, UMR CNRS 6200, Université d'Angers, 2 boulevard Lavoisier, 49045 Angers, France. michel.chrysos@univ-angers.fr
authors.forename: M
authors.initials: M
authors.lastname: Chrysos
authors.forename: I A
authors.initials: IA
authors.lastname: Verzhbitskiy
authors.forename: F
authors.initials: F
authors.lastname: Rachet
authors.forename: A P
authors.initials: AP
authors.lastname: Kouzov