Quantum Theory of Photodesorption of Neutrals from Metals: Ab Initio Calculations and Active Control

摘要

In continuation of previous work, two aspects of the ultraviolet laser-induced desorption of NO from Pt(111) and ammonia from Cu(111) are investigated using different, quantum mechanical tools. First, for NO/Pt(111) it is shown with the help of simple, ab initio electronic structure cluster calculations, that previously introduced phenomenological two- and multiple-state models are consistent with the more refined quantum chemical picture. Within this picture, the finite lifetime of a resonance state ("quenching") is microscopically a consequence of the non-adiabatic coupling of the resonance state to the metal electronic excitations. Further, both for NO/Pt(111) and ammonia/Cu(111) the possibility to actively control the desorption yields is investigated. For this purpose, time-dependent wave packet propagations based on the nuclear Schroedinger equation are used. The proposed control mechanisms are (ⅰ) thermal and (ⅱ) optical preparation of vibrational states of the adsor-bate/substrate complex. The latter strategy, which is also supported by IR transition probabilities, is found to be much more efficient.