SUBSTRATE DEPENDENCE OF ELECTRON-STIMULATED O- YIELDS FROM DISSOCIATIVE ELECTRON-ATTACHMENT TO PHYSISORBED O-2

We present measurements of O- electron stimulated desorption yields ob tained under identical experimental conditions from 0.15 monolayers (M L) of O-2 deposited onto disordered substrates consisting of 4 ML of e ither Kr, Xe, C2H6, C2H4, N2O, CH3Cl, or H2O, all condensed on Pt (pol ycrystalline). The resulting O- yield functions, for incident electron energies below 20 eV, are compared to that obtained from the O-2/Kr s olid; this allows us to assess the order of magnitude effects of the l ocal substrate environment on dissociative electron attachment (DEA) v ia the (2) Pi(u), and gas phase forbidden (2) Sigma(g,u)(+) resonances of O-2(-). We note that, in addition to electron energy losses in the substrate prior to DEA to O-2 and past-dissociation interactions of t he O- with the substrate molecules, charge or energy transfer from the O-2(-) transient anion to a substrate molecule, and capture of the in cident electron into a dissociative anion resonance of the substrate m olecule may contribute to a reduced O- yield from the physisorbed O-2. In the case of O-2 deposited on amorphous ice, we find that the O- si gnal from DEA to O-2 is completely absent for electron energies below 14 eV; we attribute this to a complete quenching of the dissociative O -2(-)((2) Pi(u), (2) Sigma(+)) resonances by the adjacent water molecu les.