Temperature dependence of the collision-induced light scattering by CH4 gas

Multiproperty empirical isotropic interatomic potentials for CH4-inert gas mixtures

An approximate empirical isotropic interatomic potentials for CH₄–inert gas mixtures are developed by simultaneously fitting the Exponential-Spline-Morse-Spline-van der Waals (ESMSV) potential form to viscosity, thermal conductivity, thermal diffusion factors, diffusion coefficient, interaction second pressure virial coefficient and scattering cross-section data. Quantum mechanical lineshapes of collision-induced absorption (CIA) at different temperatures for CH₄–He and at T = 87 K for CH₄–Ar are computed using theoretical values for overlap, octopole and hexadecapole mechanisms and interaction potential as input. Also, the quantum mechanical lineshapes of collision-induced light scattering (CILS) for the mixtures CH₄–Ar and CH₄–Xe at room temperature are calculated. The spectra of scattering consist essentially of an intense, purely translational component which includes scattering due to free pairs and bound dimers, and the other is due to the induced rotational scattering. These spectra have been interpreted by means of pair-polarizability terms, which arise from a long-range dipole-induced-dipole (DID) with small dispersion corrections and a short-range interaction mechanism involving higher-order dipole–quadrupole A and dipole–octopole E multipole polarizabilities. Good agreement between computed and experimental lineshapes of both absorption and scattering is obtained when the models of potential, interaction-induced dipole and polarizability components are used.

Empirical Interatomic Potential from Depolarized Interaction – Induced Light Scattering Spectra for Mercury

Depolarized interaction-induced light scattering spectra of mercury between 793 K and 1073 K have been used for deriving the empirical multiparameter M3SV interatomic potential. Absolute zeroth and second moments have been measured and compared with theoretical calculations using various models for the interatomic potential. The results show that it is the most accurate potential yet reported for this system.