Critical density effect on the vibrational dephasing in pure methane

The Raman isotropic v 1 band of methane has been studied along numerous isochoric lines, in a density range 0·2ρc < ρ < 2·5ρc, and over a wide range of temperature 2 . 10-3 < (T - T c)/T c < 5 . 10-1. A critical density broadening is observed even very far from the critical temperature. This effect is related in a large measure to an enhancement of the frequency modulation correlation time, an order of magnitude of which can be obtained from the band profile.