Effect of adparticle motion on time-resolved two-photon photoemission spectra of metal surfaces

The effect of the adparticle motion on the time-resolved two-photon photoemission spectra of metal surfaces on which the adparticle is adsorbed is investigated theoretically. In the two-photon photoemission process, first a pump photon excites an electron from the bulk into the anti-bonding orbital formed between the adparticle and the metal, then the adparticle begins to move, and finally a probe photon excites the electron into a free electron state above the vacuum level. It is demonstrated by the Green function method that the peak position in the energy spectrum depends on the pump–probe delay time due to the adparticle motion and it represents the potential energy for the adparticle motion.