Wave packet dynamics in the presence of a conical intersection

We present a model study of the nonadiabatic wave packet dynamics in the presence of a conical intersection. The wave packet travels essentially along a symmetric coordinate, modeling a photodissociation process, while it is stationary or makes small amplitude vibrations in the coupling modes. We explore the range of applicability of a treatment based on classical trajectories plus surface hopping, comparing it with a full quantum mechanical one. A mixed procedure, classical for the symmetric coordinate and quantum mechanical for the coupling modes, yields very accurate results and allows for a qualitative interpretation of the dynamics. We find that the dynamical behavior of a multidimensional conical intersection can be characterized in terms of a single coupling coordinate, associated with an effective coupling strength parameter.