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

Abstract

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 semi-analytically 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.