BROADENING OF VIBRATIONAL LINES BY ATTRACTIVE FORCES - ULTRAFAST RAMAN ECHO EXPERIMENTS IN A CH3ICDCL3 MIXTURE

A definitive demonstration of inhomogeneous vibrational line broadening in a liquid is made from Raman echo measurements of the sym-methyl stretching vibration of CH3I in a 50% mixture-with CDCl3. The lifetime of the inhomogeneity is found to be 4-7 ps. The source of the inhomogeneity is identified as concentration fluctuations within the first solvation shell. The range and time scale of the interaction are consistent with the predictions of Schweizer and Chandler [J. Chem. Phys. 76, 2296 (1982)] for an attractive force interaction.