A newly formulated theory for treating time-dependent molecular quantum dynamics has been used to calculate the photo-absorption spectrum of pyrazine. Comparison with quantum mechanical results shows an excellent agreement during the whole propagation, proving that the present approach, when used in a discrete variable representation scheme, converges to exact quantum results if enough grid points are used. The addition of an increasing number of bath modes to the basic four mode model is also investigated and the performance of the method discussed. (C) 2002 Elsevier Science B.V. All rights reserved.