Three pulse photon echo studies of nondipolar solvation: Comparison with a viscoelastic model

Three pulse stimulated photon echo peak shift ͑3PEPS͒ measurements were used to probe the solvation of a quadrupolar solute in three room temperature nondipolar solvents; benzene, CCl 4 , and CS 2 , and the results were compared with those for two polar solvents, methanol and acetonitrile, and one weakly polar solvent, toluene. Our data reveal three distinct solvent dynamical time scales; a sub-100 fs ultrafast component attributed to inertial motions, a slow ͑ϳ2–3 ps͒ component attributed to structural relaxation, and an intermediate time scale ͑ϳ600 fs͒ of uncertain origin. The six solvents were chosen to reflect a range of possible interactions, but exhibit similar dynamics, suggesting that similar mechanisms may be at work or that different mechanisms may exist, but occur on similar time scales. A viscoelastic continuum solvation model proposed to describe nonpolar solvation ͓J. Phys. Chem. A 102, 17 ͑1998͔͒ was used for a preliminary analysis of our data.