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 pote ntial energy can be reasonably modeled by a sum of isotropic pair potential s. 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 withou t recourse to computer simulation. If the interactions in the system are su ch that the solute's dynamic transition frequency fluctuations describe a G aussian process, this then leads to a semi-analytic theory for various spec troscopic 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 fro m molecular dynamics simulation. (C) 2001 Elsevier Science B.V. All rights reserved.