Polarizabilities collision-induced light scattering

Several types of collision-induced light scattering spectra are known. We have already mentioned the depolarized translational spectra of rare gas pairs and bigger complexes which arise from the anisotropy of the diatom polarizability. Contrary to the infrared inactivity of like pairs, e.g., Ar-Ar like pairs are Raman active. Furthermore, polarized translational spectra... 

Collision-induced light scattering is the name for the Raman spectroscopy that arises from the interaction-induced variations of the polarizability of a sample. For a description of the scope of CILS, we consider briefly two somewhat extreme cases, a tenuous gas and a liquid. 

In general, the polarizability is a tensor whose invariants, trace and anisotropy, give rise to polarized and fully depolarized light scattering, respectively. Collision-induced light scattering is caused by the excess polarizability of a collisional pair (or a larger complex of atoms or molecules) that arises from the intermolecular interactions. In Section I.l, we are concerned with the definition, measurement, and computation of interaction-induced polarizabilities and their invariants. 

D. B. DuPre and J. P. McTague. Pair polarizability of hydrogen atoms. Relation to collision induced light scattering and dielectric phenomena in rare gases. J. Chem. Phys., 50 2024-2028 (1969). 

Y. Le Duff, A. Chave, B. Dumon, H. Idrissi, and M. Thibeau. Two-body collision induced light scattering Effect of the spatial extension of the polarizability for conducting spheres. Phys. Lett. A, 73 307-308 (1979). 

E. F. O Brien, V. P. Gutschick, V. McKoy, and J. P. McTague. Polarizability of interacting atoms relation to collision induced light scattering and dielectric models. Phys. Rev. A, 5 690-696 (1973). 

F. Barocchi and M. Zoppi. Collision induced light scattering spectra and pair polarizability of gaseous argon. Phys. Lett. A, 66 99-102 (1978). 

The influence of Van der Waals interactions on the polarizability of interacting molecules manifests itself in deviations from the Clausius-Mosotti equation , in the Kerr effect and in collision induced light scattering . Although measurements of these effects are all performed on bulk systems in thermodynamical equilibrium and not on Van der Waals molecules per se, we will nevertheless say a few words about pair polarizabilities, because, just as in the case of the collision induced IR absorption, much can be learned about Van der Waals interactions from the comparison of experimental and computational results. 

In summary, since the early 1980s or so, collision-induced light scattering experiments on molecular fluids have demonstrated that the study of the collision-induced absolute-unit spectra (depolarized and/or isotropic ones) is an useful tool, and up to now the only one, to measure multipolar polarizabilities of molecules. 

S.M. El-Sheikh, G.C. Tabisz, A.D. Buckingham, Collision-induced light scattering by isotropic molecules the role of the quadmpole polarizability. Chem. Phys. 247, 407-412 (1999)... 

Maroulis and Hohm have calculated the dipole-dipole, dipole-quadrupole, and dipole-octopole polarizabilities of Ge(CH3)4 using the FF procedure at the HF, MP2, and B3LYP levels of approximation. From comparison with their data deduced from collision-induced light-scattering experiments, they have concluded that reliable dipole-dipole polarizability values are obtained, that good agreement is achieved for the dipole-octopole polarizability but that there remains a discrepancy for the dipole-quadrupole polarizability (Table 3). 

At present, in spite of the well-known fact that the interaction of atoms and molecules leads to the changing of their multipole moments and (hyper)polariz-abilities [1-3], only the simple moments and polarizabilities of interacting molecules such as interaction-induced dipole moments and dipole polarizabilities have widely studied. Nevertheless, the induced dipole moments and polarizabilities play the important role in understanding the collision-induced absorption, collision-induced Rayleigh scattering or collision-induced Raman light scattering [4-9],... 

Here, a. and a L are the polarizabilities of the diatom parallel and perpendicular to the internuclear separation, R12. The electrostatic theory accounts for the distortions of the local field by the proximity of a point dipole (the polarized collisional partner) and suggests that the anisotropy is given by ft Rn) 6intermolecular interactions). This is the so-called dipole-induced dipole (DID) model, which approximates the induced anisotropy of such diatoms often fairly well. It gives rise to pressure-induced depolarization of scattered light, and to depolarized, collision-induced Raman spectra in general. 

D. A. Dunmur, M. R. Manterfield, and D. J. Robinson. Depolarized light scattering studies of the collision induced polarizability anisotropy of atoms and spherical top molecules. Molec. Phys., 50 573-583 (1983). 

N. Meinander, A. R. Penner, U. Bafile, F. Barocchi, M. Zoppi, D. P. Shelton, and G. C. Tabisz. The spectral profile of the collision induced translational light scattering by gaseous CH4 Determination of the pair polarizability anisotropy. Molec. Phys., 54 493-503 (1985). 

Frommhold, L. (1981). Collision-induced scattering of light and the diatom polarizabilities. Adv. Chem. Phys. 46, 1. 

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