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

Vibrational lifetime (T1) data for the asymmetric CO stretching mode of W(CO)6 in supercritical ethane and carbon dioxide as a function of temperature at various fixed densities are compared to a recent extended hydrodynamic theory [1]. In ethane at the critical density, as the temperature is raised, T1 initially becomes longer, reaching a maximum ∼70 K above the critical temperature. T1 decreases with further increase in temperature. The theory is able to reproduce this behavior nearly quantitatively without free parameters. At high density in ethane and in CO2, the inverted temperature dependence is not observed, in agreement with theoretical calculations.