Ion energy distributions from photon- and electron-stimulated desorption: Reflection approximation

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Abstract
A simple final-state potential consisting of an exponential repulsion and an image term is used in conjunction with a Franck-Condon model to fit ion energy distributions (IED) resulting from photon- or electron-stimulated desorption. For all of the metal-adsorbate systems studied the IED is essentially a reflection of the ground vibrational state of the chemisorbed species, i.e., a Gaussian with slight asymmetry, usually to the high-energy side, caused by the curvature of the simple exponential repulsion. In at least two cases, however, the asymmetry is to the low-energy side. We suggest that this result could be due to a reversed curvature in the effective final-state potential indicative of multiple curve crossings (electron hopping) from ion to atom and back as the final species desorbs.