Lineshape data have been obtained for the isotropic Raman spectra of H
D and para H-2 diluted in liquid and hypercritical argon. The observed
profiles near 2rho(c), are interpreted in terms of pure vibrational d
ephasing and fast modulation process. In the critical region an inhomo
geneous broadening is observed; it is superimposed in the HD case, on
a rotational contribution. A detailed analysis of the Q spectra obtain
ed for the normal H-2-argon system along the critical isochore provide
s evidence for the role of density fluctuations near the liquid-gas cr
itical point.