Femtosecond wavepacket dynamics on strongly coupled potential energy surfaces

An overview is given of various results of ab initio quantum dynamical simu lations on conically intersecting potential energy surfaces. Here, the nona diabatic coupling effects are typically very strong, leading to a femtoseco nd (fs) population decay of the upper electronic state and to a diffuse app earance of the corresponding band in the electronic spectrum. For the lower electronic state we demonstrate the possibility of a bifurcation of the wa vepacket that can lead to a manifestation of the geometric phase. The examp les chosen to illustrate these phenomena are triatomic hydrogen, sulfur dio xide, and the radical cation of benzene. The latter systems features a comp lex "web" of different multidimensional, partly coalescing, conical interse ctions between up to eight potential energy surfaces. The resulting stepwis e femtosecond decay processes give rise to a highly complex vibronic dynami cs that is currently being modeled to an increasing degree of sophisticatio n. (C) 2000 John Wiley & Sons, Inc.