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 ${\mathrm{N}}_2$. The data were obtained as a function of reduced temperature [$\epsilon =\frac{(T-T_c)}{T_c}$] under isochoric conditions, and analysis of the data clearly shows for the first time that inhomogeneous broadening is dominant when $\epsilon <0.001\mathrm{}$ 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.