Resonance Interference in a Three-level System with Dynamic Coupling of the Intermediate State to a Vibrational Mode

Coherent electronic transitions are analysed in a three-level system where the intermediate level is strongly coupled to a classical nuclear mode the dynamics of which is explicitly incorporated. Such a configuration is representative of scanning tunnelling microscopy through a molecular adsorbate. Solution of the equations of motion gives a drop in the overall transition probability per unit time (current) from the initial to the final state when these two states are in resonance. This observation differs from resonance effects obtained by second-order perturbation theory in stationary nuclear environments, and is associated with the motion of the intermediate state level through the resonance region.