Abstract. Heterogeneous electron transfer across interfaces is frequently discussed on the basis of Marcus Theory taking into account rearrangements of the solvent along a nuclear coordinate q. The electron transfer process itself occurs via tunnelling through a barrier normal to the interface. The key point is not whether tunnelling occurs, but whether thermally activated solvent fluctuations initiate the tunnelling. Here, we discuss the role of thermally activated tunnelling in heterogeneous electron transfer versus direct electron transport due to strong electronic coupling to a metal substrate. As a model system we investigate the ultrafast dynamics of electron transfer at amorphous ice-metal interfaces (4-6 bilayers D2O/Cu(111) and Ru(001), respectively) by time-resolved two-photon photo-electron spectroscopy. We find that the electron transfer rate is independent of temperature within the first 500 fs after excitation, which demonstrates that for this system interfacial electron transfer occurs in the strong coupling limit and that thermally assisted tunnelling plays a negligible role..
The publication is available at link doi:10.1088/1367-2630/9/10/394