Molecular theory of three-pulse photon echoes for solutes in non-polar fluids

For a simple molecular solute in a simple non-polar liquid solvent the potential energy can be reasonably modeled by a sum of isotropic pair potentials. In this case various time-correlation functions, including the solute's (transition) frequency-frequency time-correlation function (also called the solvation correlation function), can be calculated semianalytically without recourse to computer simulation. If the interactions in the system are such that the solute's dynamic transition frequency fluctuations describe a Gaussian process, this then leads to a semi-analytic theory for various spectroscopic observables, including the three-pulse photon echo intensity. In this paper we describe such a theory of the photon echo intensity. For two different model systems our theoretical results compare well with those from molecular dynamics simulation. (C) 2001 Elsevier Science B.V. All rights reserved.