We present data showing the energy dependence of the electron-stimulated desorption signal and charge-trapping cross section for molecules of CF4 condensed onto a multilayer Kr film. In both cases, these phenomena occur via dissociative electron attachment (DEA) to the molecule. As with pure CF4 films, the only detectable desorbed signal from the film is F-, generated via the lowest of two CF4- resonant states associated 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 cross section for DEA in the gas phase. The enhancement in the DEA cross section is estimated to be between a factor 5 and 9. This enhancement reflects an increased probability of survival against autodetachment for intermediate anion stares that results from interaction with-the electronic polarization field they induce on the Kr surface.