A velocity-memory model for the spectral lineshape from the Doppler to the collision regime

Abstract The radiator speed-memory has been recently shown to have important consequences for spectral lineshapes in the collision regime. This speed-memory controls the speed changing collisional mechanism, which becomes crucial when inhomogeneities arise from the speed dependence of the line broadening and/or shifting parameters. The extension of such a memory approach to lower densities requires the introduction of a pertinent velocity -memory function (instead of that based on speed ) in order to also account for the confinement narrowing. A simple velocity-memory model which describes separately the correlation processes for the velocity-modulus (i.e. the speed) and for the velocity-orientation is proposed. The resulting analytical line profile is derived within the impact kinetic equation. The evolution of the resulting lineshape vs. the density is studied from the Doppler to the collision regime for the H 2 –Ar prototype system. The specific roles of the velocity-orientation memory and speed memory processes are analyzed in a wide range of density, for which both confinement narrowing and speed dependence of relaxation parameters influence the spectral lineshape.