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 23 band of CO2-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 CO2-gas densities. Evidence for a near-entirely depolarized Raman band is provided, with integrated depolarization ratio int=67.16, closely approaching the upper bound max=67. 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 1 and antisymmetric 3 stretching vibrations are incorporated.
Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry