COMPARISON AND ANALYSIS OF ROTATIONALLY INELASTIC-COLLISION MODELS DESCRIBING THE Q-BRANCH COLLAPSE AT HIGH-DENSITY

The fitting laws usually employed to model the relaxation matrix and, therefore, to account for the collisional narrowing of the Q-branch ha ve been tested against the density dependence of the isotropic Raman b and width (GAMMA) for nitrogen. The behavior of GAMMA has been theoret ically studied in a wide density range: from 10 to 1072 amagat at 295 K in gas and liquid phases. The independent binary collision (IBC) app roach has been applied to reproduce the density dependence of GAMMA in this domain. Quite surprisingly, the IBC expression reproduces the de nsity variation of GAMMA rather well, despite the limited validity of such an approach. Rotational energy relaxation cross sections (sigma(E )' and sigma(E)) are also employed for comparison. Relaxation models t hat do not provide the experimental value of sigma(E) cannot be used t o describe the Q-branch collapse in the limit of extreme narrowing. We find that at the stage of narrowing the reconstructed dephasing rate is essentially dependent on the accepted model of rotational relaxatio n.