A MICROSCOPIC DESCRIPTION OF DISSIPATION IN SYSTEMS WITH STRONG VIBRONIC COUPLING - THE S-1 AND S-2 ABSORPTION-SPECTRA OF PYRAZINE

The photoabsorption spectrum of the vibronically coupled electronic S- 1/S-2 states of pyrazine has been calculated. The dynamics of the mole cule is described within the reduced density matrix formalism. The fou r most important vibrational modes are included in the reduced density matrix and the 20 remaining modes are considered as bath. In the mast er equation, the system-bath interaction is treated within second-orde r perturbation theory and the corresponding operators are derived from a microscopic model. The resulting non-Markovian dissipation operator is evaluated numerically. The calculated spectra are in good agreemen t with experiment and benchmark MCTDH calculations. (C) 1998 Elsevier Science B.V. All rights reserved.