Translational energy distribution in hot electron mediated photodesorption: a one-dimensional quantum mechanical calculation of NO/Pt(111) and SO2/Ag(111)

An one-dimensional (along the adsorbate-surface coordinate) quantum mechani cal calculation within the framework of the Antoniewicz model has been perf ormed for understanding the translational energy distribution in desorption of chemisorbed systems such as NO/Pt(111) and SO2/Ag(111). The potential e nergy curve of the ground state is constructed from known adsorption proper ties and that of the excited state is constructed by adding a Coulombic ter m for the image charge stabilization. For these model potentials, the one-d imensional Schrodinger equation is solved exactly using the Cooley-Numerov integrator. This enables one to follow the time evolution of the wavepacket while the excited state is allowed to decay exponentially with a mean life time. The translational energy distributions of the desorbed molecules are obtained by mapping out the Franck-Condon overlap of the final state wavefu nction with the continuum states of the ground PES. The effects of the shap e of the potential energy curves and the residence lifetime in the excited state are examined. It is found that the calculated average translational e nergies compare with those experimentally measured for both systems. It als o appears that the translational temperature is hotter for adsorbates that are more strongly bonded to the substrates. (C) 2000 Published by Elsevier Science B.V. All rights reserved.