The effects of different substrates on the electron stimulated desorption dynamics of O- from physisorbed O-2

We report condensed phase measurements of kinetic energy (E-k) distributions of O-, produced by dissociative electron attachment (DEA) at 6 eV incident electron energy; they are obtained under identical experimental conditions from submonolayer quantities of O-16(2) deposited on disordered multilayer substrates of O-18(2), Ar, Kr, Xe, CH4, and C2H6, all condensed at 20 K on polycrystalline platinum (Pt). The results suggest that the desorption dynamics of O- DEA fragments is, in part, determined by large angle elastic scattering of O- prior to desorption, as well as the net image charge potential (E-p) induced in the condensed dielectric solid and the Pt metal, The measurements also indicate that, particularly at small Kr substrate thicknesses, the E-p may not necessarily be uniform across the surface, but may fluctuate due to surface roughness. Thus, in addition to energy losses in the substrate prior to, and during, DEA, these effects may influence the dissociation dynamics of the O-2(-) resonance itself, as well as the desorption of the DEA O- fragment. (C) 1997 American Institute of Physics.