Memory effects in speed-changing collisions and their consequences for spectral line shape - II. From the collision to the Doppler regime

The kinetic model accounting for speed-memory effects on the spectral line shape proposed in I [D. Robert, L. Bonamy, Eur. Phys. J. D 2, 245 (1998)] is extended for any density range, within the binary collision framework. The additional Doppler contribution requires to consider the 3D velocity-memory function instead of the 1D speed one, with distinct treatments for the velocity-orientation and velocity-modulus memory mechanisms. Both the collisional confinement narrowing of the Doppler distribution and the radiator speed-dependence of the collisional broadening and shifting parameters are thus conveniently taken into account. In the high density regime, this model leads to the same results as in I. At lower densities, it generalizes the very well-known hard and soft collision models for the Dicke narrowing of the Doppler distribution, but it also includes the second source of inhomogeneity tied to the speed-dependent collisional parameters and, concomitantly, the speed class exchanges. Numerical applications to H-2-N-2 and H-2-Ar gaseous mixtures are in close agreement with experiments. This allows one to clearly analyze the specific role of speed and velocity memory effects on the line profile.