THEORETICAL DESCRIPTION OF DISSIPATIVE VIBRATIONAL DYNAMICS USING THEDENSITY-MATRIX IN THE STATE REPRESENTATION

Ultrafast dissipative dynamics of vibrational degrees of freedom in mo lecular systems in the condensed phase are studied here. Assuming that the total system is separable into a relevant part and a reservoir, t he dynamics of the relevant part can be described by means of a reduce d statistical density operator. For a weak or intermediate coupling be tween the relevant part and the reservoir, it is possible to derive a second-order master equation for this operator. Using a representation of the reduced statistical operator in an appropriate molecular basis set, vibrational dynamics in a variety of potential energy surfaces c an be studied. In the numerical calculations, we focus on the dissipat ive dynamics under the influence of external laser fields. In the firs t example, vibrational wave-packet dynamics and time-resolved pump-pro be spectroscopy of molecular systems with nonadiabatically coupled exc ited-state potential energy surfaces is presented. In the second part, we show how an intense laser field modifies the wave-packet motion on to two radiatively coupled potential energy surfaces. Finally, the con trolled preparation of definite vibrational states in a triatomic mole cule with infrared laser pulses is considered taking relaxation and de phasing processes into account. (C) 1996 John Wiley & Sons, Inc.