ISOTOPE EFFECT IN SURFACE PHOTOCHEMICAL PROCESSES: EXPERIMENT AND THEORY

Abstract

A photochemical process in the adsorbate state has an inherent isotope or mass effect. This is because the presence of a solid surface introduces efficient relaxation channels for the electronically excited molecule. Competition between the chemical event and the quenching process is mass-dependent. Depending on the details of the dynamic energy transfer process, the isotope effect in a surface photochemical event can depend on either the mass or the internal reduced mass of the desorbing/dissociating particle. Measurements of isotope effect in UV surface photochemistry have provided insight into two mechanistic models, i.e., the classic Menzel-Gomer-Redhead (MGR) model and its recent variation, the vibration-mediated UV photodesorption (VMPD) model.