Extension of the energy-corrected sudden model to anisotropic Raman lines: Application to pure N₂

The Energy-Corrected Sudden (ECS) model is a well-established dynamical model to calculate rovibrational isotropic Raman linewidth and also to describe overlapping between lines through the off-diagonal elements of the relaxation matrix. The extension of this model to anisotropic Raman or infrared lines has been previously performed through the expansion of the tetradic (four indices) relaxation supermatrix elements in terms of dyadic (two indices) mechanical cross sections. This model required new parameters in the diagonal elements of the dyadic matrices that are the relaxation cross sections of rotational angular momentum and of its associated second-order tensor. In this paper, a new approach of the extension of the ECS model for anisotropic Raman and infrared branches is proposed, and developed on a strong physical basis. This new model only needs the original ECS parameters determined through a fit of the experimental isotropic Raman Q linewidths to generate anisotropic Raman and infrared linewidths as well as line mixing coefficients.