State filtering by a bath: up to 24 mode numerically exact wavepacket propagations

Numerically exact wavepacket calculations have been performed on a subsyste m coupled to an explicitly treated finite bath, using recently developed te chniques within the framework of the multiconfiguration time-dependent Hart ree (MCTDH) method. The subsystem of 4 nuclear modes and 2 interacting elec tronic states was coupled to a bath of up to 20 harmonic oscillators. The r esults show that the presence of the bath leads to a clear, long-lived stru cture in the autocorrelation function. Surprisingly, this regular structure becomes more dominant as the number of bath modes is increased, and is due to excited states above the conical intersection. Furthermore, it lasts fo r times much longer than that of the inter-state population relaxation proc ess. (C) 1999 Elsevier Science B.V. All rights reserved.