AVS 53rd International Symposium
    Surface Science Wednesday Sessions
       Session SS2-WeM

Paper SS2-WeM2
Adsorption-State-Dependent Subpicosecond Photoinduced Desorption Dynamics

Wednesday, November 15, 2006, 8:20 am, Room 2004

Session: Electronic and Vibrational Excitations and Dynamics
Presenter: P. Szymanski, Brookhaven National Laboratory
Authors: P. Szymanski, Brookhaven National Laboratory
A.L. Harris, Brookhaven National Laboratory
M.G. White, Brookhaven National Laboratory and SUNY Stony Brook
N. Camillone III, Brookhaven National Laboratory
Correspondent: Click to Email
Femtosecond laser excitation has been used to initiate desorption of molecular oxygen from the (111) surface of Pd and study the adsorption-state-dependence of the substrate-adsorbate coupling. The relative populations of the two chemical states, peroxo (O@sub 2@@super 2-@) and superoxo (O@sub 2@@super -@), were varied by changing the total coverage. Two-pulse correlation measurements reveal that the O@sub 2@-substrate coupling times are dominated by a sub-500 fs response that is independent of O@sub 2@ coverage. In contrast, the measurements show a systematic coverage dependence of the photodesorption yield and the nonlinearity of the fluence-dependence. Thus, though the photoinduced desorption from the two states is driven primarily by the same electron-mediated mechanism, the desorption efficiency from the superoxo state is greater than that from the peroxo state. These results are discussed in the context of the two-temperature model, treating the dependence of the desorption yield on absorbed laser fluence together with the dynamics in a global simulation to extract coupling strengths and understand the adsorption-state-dependence of the desorption efficiency.