ABSOLUTE CROSS-SECTION FOR DISSOCIATIVE ELECTRON-ATTACHMENT TO CF4 CONDENSED ONTO MULTILAYER KRYPTON

We present data showing the energy dependence of the electron-stimulat ed desorption signal and charge-trapping cross section for molecules o f CF4 condensed onto a multilayer Kr film. In both cases, these phenom ena occur via dissociative electron attachment (DEA) to the molecule. As with pure CF4 films, the only detectable desorbed signal from the f ilm is F-, generated via the lowest of two CF4- resonant states associ ated with DEA. However, both resonant states are implicated in charge trapping via the formation of fragment ions at the surface. The charge -trapping cross section at maximum, is 4-7 times greater than the cros s section for DEA in the gas phase. The enhancement in the DEA cross s ection is estimated to be between a factor 5 and 9. This enhancement r eflects an increased probability of survival against autodetachment fo r intermediate anion stares that results from interaction with-the ele ctronic polarization field they induce on the Kr surface.