QUANTUM-MECHANICAL STUDY OF LASER-INDUCED DESORPTION OF PHYSISORBED MOLECULES ON DIELECTRIC SURFACES

In order to understand the surface binding of a diatom/ionic crystal system, we investigate the behaviors of the diatomic molecule HF on a LiF(001) surface. We firstly calculate the gas molecule/surface interaction potential. The polar angle of the molecule is proved to play a major role in a desorption event. By applying the time-dependent perturbation theory and the Fermi golden rule, with the coupling terms of the interaction potential chosen analytically, the residence time and two different photodesorption rates of the adsorbate are examined. This model also predicts that the desorption probability depends on the initial states of adsorbate and on the shape of the Morse potential. In addition, an estimate of the photodesorption rate has been made by increasing the energies of the incident photon and laser intensity. We present here two possible approaches for evaluating the transition rate. The first one is applied to keep a constant laser intensity with varying photon frequency, while the second one is examined to maintain a constant laser frequency with changing the intensity. The results would be valuable in characterizing the coupling between the laser and surface bond.