Novel Isotope Effect in Coherent Non-adiabatic Dynamics Induced by an Attosecond Pulse

Ultrafast laser pulses have a broad range in energy inducing coherent population of multiple electronic states within one molecule. We discuss the case when the pumped wave packets reach the region of the strong non-adiabatic coupling and exchange their population. We describe both numerically and analytically new and essentially quantum effect enabled by a coherence between the electronic states. We discuss the dynamics in the manifold of bound singlet states of N 2 [1] , [2] and dissociative states of LiH [3] . The effect originates from the quantal interference between the nuclear wavepackets evolving on two coupled electronic potentials (see Fig. 1 ). It is not limited to the light nuclei, like the effect of tunneling, and is dynamical in nature. The key point is that the non-adiabatic transfer takes place between two or more already populated electronic states. In this novel type of initial state the non-adiabatic amplitude exchange between the coupled electronic states strongly depends on isotopic composition and in the case of bound electronic potentials on the history of the nuclear dynamics. We show that isotope substitution can also lead to an opposite direction of the transfer, therefore can be used as a tool to control the pathway of the photochemical reaction.