Vibrational lifetimes and spectral shifts in supercritical fluids as a function of density: Experiments and theory

Vibrational lifetime and spectral shift data for the asymmetric CO stretchi ng mode of W(CO)(6) in supercritical ethane, carbon dioxide, and fluoroform at; a function of density at two temperatures are presented, and the lifet ime (T-1) measurements are compared to theory. The data and cheery are refi nements of previous work. Measurements at zero density allow the contributi on from solute-solvent interactions to be separated from strictly intramole cular contributions to T-1. The results in the polyatomic SCFs are compared to data in Ar. The density functional/thennodynamic theory(1) has been ext ended to include contributions at large wavevector (k). Very good, quantita tive agreement between theory and data taken in ethane and fluoroform is ac hieved, but the agreement for data taken in carbon dioxide, while reasonabl e, is not as good. The theory uses a variety of input information on the SC F properties obtained from the fluids' equations of state and other tabulat ed thermodynamic data. The solute-solvent spatial distribution is described in terms of hard spheres. The theory is able to reproduce the data without solute-solvent attractive interactions or clustering in the calculation of the spatial distribution.