Temperature dependence of solute vibrational relaxation in supercritical fluids: experiment and theory

Vibrational lifetime (T-1) data for the asymmetric CO stretching mode of W( CO)(6) in supercritical ethane and carbon dioxide as a function of temperat ure at various fixed densities are compared to a recent extended hydrodynam ic theory [1]. In ethane at the critical density, as the temperature is rai sed, T-1 initially becomes longer, reaching a maximum similar to 70 K above the critical temperature. T-1 decreases with further increase in temperatu re. The theory is able to reproduce this behavior nearly quantitatively wit hout free parameters. At high density in ethane and in CO2, the inverted te mperature dependence is not observed, in agreement with theoretical calcula tions. (C) 2000 Published by Elsevier Science B.V.