Dynamics of NH3 photodesorption from GaAs(100): Role of electronic quenching

Abstract

A vibration-mediated UV photodesorption (VMPD) model is presented to account for the large isotope effect observed in the nonthermal UV photodesorption of ammonia from GaAs(100). In this mechanism, electronic excitation and deexcitation of the adsorbed molecule results in intramolecular vibrational excitation. The internal vibrational energy can couple to the adsorbate–surface coordinate and lead to desorption. In contrast to the classic Menzel–Gomer–Redhead model, the VMPD model predicts that the isotope effect in desorption is determined by the internal reduced mass of the leaving particle. Both classical Newtonian and semiclassical wave packet formulations are derived.