Water and D2O single molecules at very low coverage (~1%) are studied on Pd(111) surface. It was observed in experiments that diffusion rate of adsorbates depends on the voltage on the tip (see movies). Further research showed that threshold exists for both H2O and D2O above which diffusion rate increases dramatically (see the graph). It was found that the value of threshold voltage corresponds very well to the activation energy of bending modes of the molecules. Isotope effect observed in experiments allows us to conclude that electrons exice bending mode ot adsorbates, which is the dissipates into translation mode giving rise to the diffusion rate. The mechanism of coupling between bending and translation modes is still under analysis. The paper on the topic will be published soon.

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