Vibrational Raman Effect: A New Experimental Probe of the Liquid-Vapor Critical Phenomenon

Accurate interferometric line-shape data have been obtained for the pure vibrational (Q branch) component in the Raman spectrum of supercritical N₂. The data were obtained as a function of reduced temperature [ε=(T-Tc)Tc] under isochoric conditions, and analysis of the data clearly shows for the first time that inhomogeneous broadening is dominant when ε<0.001 at the critical density. It is proposed that in this static dephasing limit it should be possible to extract information pertaining to the statistical distribution of "local" densities within the fluid.