Molecular photoexcitation in a medium: Density operator approach

Abstract

The excitation of a molecule in a medium, by absorption of a light pulse, is described in terms of density operators and the Liouville–von Neumann equation for the whole system. This is divided into a primary region containing the molecule and its close neighbors to which it may be bonded or strongly interacting, plus a secondary region including the remaining medium. A time-dependent self-consistent field procedure factors the density operator into primary and secondary components, each of which interacts with the applied light field. Direct absorption and indirect absorption are described with superoperators in a Liouville space formalism. Equations for the response of the primary region are developed assuming a stochastic medium. The treatment allows for dissipation due to collective electronic or vibrational excitations in the medium. Applications to photodesorption of molecules from metal surfaces are briefly discussed. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 367–375, 2000