Coherent excitation of wavepackets in two electronic states. Interference effects at an avoided crossing

We present quantum mechanical calculations of the nonadiabatic time-evolution of molecular states in a model system. The simultaneous coherent excitation of two different electronic states is simulated. The repulsive potential energy curves representing the excited states undergo an avoided crossing, which causes the interference of the two wavepackets. The effect of interference on the final populations after dissociation exhibits a characteristic pattern as a function of the exciting radiation frequency.