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 s ystem, we investigate the behaviors of the diatomic molecule HF on a L iF(001) surface. We firstly calculate the gas molecule/surface interac tion potential. The polar angle of the molecule is proved to play a ma jor role in a desorption event. By applying the time-dependent perturb ation 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 m odel also predicts that the desorption probability depends on the init ial states of adsorbate and on the shape of the Morse potential. In ad dition, an estimate of the photodesorption rate has been made by incre asing the energies of the incident photon and laser intensity. We pres ent here two possible approaches for evaluating the transition rate. T he first one is applied to keep a constant laser intensity with varyin g photon frequency, while the second one is examined to maintain a con stant laser frequency with changing the intensity. The results would b e valuable in characterizing the coupling between the laser and surfac e bond.