Induced contributions in the Rayleigh band of gaseousH2S

Polarized and depolarized rotational Raman spectra of gaseous ${\mathrm{H}}_2$S have been measured at room temperature and different pressures, together with the Q branch of the ${\nu }_1$ band used as an internal standard. Isotropic and anisotropic spectra are found to be affected by ‘‘collision’’-induced effects which are not completely explainable in terms of the first-order dipole–induced-dipole (DID) mechanism. Integrated intensities, depolarization ratios, and spectral shapes are compared with theoretical predictions in order to discriminate between the different scattering mechanisms, which are accounted for in the framework of the multipolar and higher-order polarizability series expansion. Higher-order polarizabilities are considered for induced effects only, the laser power being fairly low. At the density considered, the anisotropic integrated intensity is due to ordinary rotational and induced contributions, the first-order DID one accounting for most of the measured intensity. Other induced contributions appear in the frequency range 100–450 ${\mathrm{cm}}^{\mathrm{-}1}$, the DID scattering being confined to low frequency. Their origin can be understood by analyzing the measured isotropic spectra. The rotational induced contribution involving the dipole-quadrupole polarizability tensor (αA contribution) is mainly responsible for the broad isotropic spectrum extending up to 450 ${\mathrm{cm}}^{\mathrm{-}1}$, whereas an induced contribution involving the first hyperpolarizability is negligible. It has been possible to estimate $A_{123}$,$1^2$+${\mathrm{A}}_{123}$,$3^2$ =3 A${̊}^8$.