Application of mode-coupling theory to solvation dynamics

Abstract

Mode-coupling theory (MCT) is applied to the dynamics of electronic-state solvation. Solvation dynamics in two solvents, propylene carbonate and n-butylbenzene, are analyzed by both mode-coupling theory and more standard empirical methods. Fits of the solvation response function allow all the MCT parameters to be extracted. In both liquids, the \ensuremath{\alpha} and \ensuremath{\beta} regions overlap strongly and a simultaneous fit of both regions is required. In the case of propylene carbonate, both \ensuremath{\beta}- and \ensuremath{\alpha}-relaxation components are clearly present. The crossover temperature ${\mathit{T}}_{\mathit{c}}$ and exponent parameter \ensuremath{\lambda} agree with those found by the light-scattering experiments of Du et al. [Phys. Rev. E 49, 2192 (1994)], showing that these parameters are independent of experiment, as predicted by MCT. In n-butylbenzene, both a standard fit without \ensuremath{\beta} relaxation and a MCT fit including \ensuremath{\beta} relaxation agree well with the data. The value of ${\mathit{T}}_{\mathit{c}}$ found disagrees with the value found by the impulsive stimulated thermal scattering experiments of Yang, Muller, and Nelson. In both liquids, the fits extend well above the melting points into the low-viscosity, normal liquid range. \textcopyright{} 1996 The American Physical Society.