Numerical modelling of the excitation energy dependence of adsorbate photochemistry at metal surfaces

The energy dependence of the photodesorption cross-section in the OCS/Ag(11 1) system is interpreted in terms of the hot electron attachment model incl uding the electron cascade process and the substrate absorbance. An electro n attachment level 3 eV above the Fermi level gives the best fit of the exp erimental action spectrum. The sensitivity of the fit to a variety of param eters is analysed. The fit is a strong function of attachment level energy. The weight of other parameters (attachment level width, surface-adsorbate barrier, secondary electron cascade profile) is less significant. It is sho wn that the model may reproduce the reported universal wavelength dependenc e of photodesorption on different metal substrates only if the attachment l evel is located a constant distance from the metal Fermi level. (C) 2001 El sevier Science B.V. All rights reserved.