Speed-dependent line-shape model analysis from molecular-dynamics simulations: The collisional confinement narrowing regime

A critical analysis of the speed-dependent spectral line-shape models is presented. With this aim, a comparison of these models is done with molecular-dynamics results for ${\mathrm{H}}_{2}\ensuremath{-}X$ gaseous mixtures. This allows us to get a clear understanding of the consequences of the assumptions underlying these models on the line profile. This proves the requirement to introduce, in the collisional confinement regime, distinct treatments for the velocity-orientation and velocity-modulus memory mechanisms. Such a requirement applies when the goal is to get both a high accuracy with experimental stimulated Raman profiles and a high consistency with molecular dynamics (i.e., with first principles).