Vibrational quantum dynamics at metallic surfaces

In this chapter, we investigate the effect of non-adiabatic coupling on the chemical dynamics of small adsorbates at metallic surfaces from a purely quantum mechanical perspective. It is argued that the simple picture of nuclei moving adiabatically on a potential energy landscape formed by the electrostatic interactions with instantaneously reacting electrons is not fully adequate for describing reactions in the condensed phase. A theory of non-adiabatic coupling for adsorbates at metallic surfaces in the weak coupling regime is introduced and first principle perturbative expressions for the associated transition rates are derived. It is explained how the effect of non-adiabaticity on the quantum dynamics of vibrating adsorbates at metals can be investigated using the reduced density formalism. The transient dissipative vibrational dynamics is presented for a number of examples relevant to the field of surface science: adsorbate relaxation dynamics demonstrates the importance of anharmonicity and intermode coupling mediated by the surface electrons, infrared laser excitations show the importance played by timescales to achieve selectivity, and the inelastic current contributions in scanning tunnelling microscopy are used to explain impurity migration dynamics induced by impinging electrons.