Non-adiabatic effects in electron tunneling in molecular junctions

Most models on electron transport in molecular junctions implicitly assume that there is only one potential energy surface (PES) involved in transport. The current and/or the voltage across the junction may invalidate this assumption in a number of important situations. We recently developed a model for the description of STM-induced unimolecular surface reactions as an electronic cotunneling process that takes explicitly into account the possibility of coupling of two PES via the interaction between the molecule and the electrode as described by the self-energy. In this contribution we extend our model in the framework of a theory of nonadiabatic tunneling developed by Zhu and Lin. Our results may be of importance in the context and current and voltage-induced processes in nano-junctions and also on a more fundamental level to broaden our understanding of the relationship between molecular conductance and electron transfer reactions.