Femtosecond wavepacket dynamics on strongly coupled potential energy surfaces

An overview is given of various results of ab initio quantum dynamical simulations on conically intersecting potential energy surfaces. Here, the nonadiabatic coupling effects are typically very strong, leading to a femtosecond (fs) population decay of the upper electronic state and to a diffuse appearance of the corresponding band in the electronic spectrum. For the lower electronic state we demonstrate the possibility of a bifurcation of the wavepacket that can lead to a manifestation of the geometric phase. The examples chosen to illustrate these phenomena are triatomic hydrogen, sulfur dioxide, and the radical cation of benzene. The latter systems features a complex “web” of different multidimensional, partly coalescing, conical intersections between up to eight potential energy surfaces. The resulting stepwise femtosecond decay processes give rise to a highly complex vibronic dynamics that is currently being modeled to an increasing degree of sophistication.