ELECTRON-CAPTURE INDUCED REACTIONS IN CF4 CLUSTERS

Electron capture by van der Waals aggregates of CF4 and the subsequent decomposition into negatively charged product ions have been studied in a beam experiment. Apart from the fragments known from dissociative electron attachment to the isolated compound (F- and CF3-), a variety of larger ionic complexes such as M(n)-, M(n).F-, and M(n).CF3-, n greater-than-or-equal-to 1 (M = CF4), are observed. Their formation probabilities as a function of electron energy indicate that the initial step of electron capture proceeds via formation of an individual CF4- within the target cluster which then decomposes. Within the many products the monomeric anion CF4- in its relaxed configuration is generated. In that case, a relaxation energy of more than 3.5 eV has to be distributed among the target aggregate. CF4- has not been observed in the gas phase before. It is likely that it represents a metastable species with respect to autodetachment (negative adiabatic electron affinity of CF4). A time-of-flight analysis reveals that all ionic products are formed with low translational energy, including F- and CF3-. The latter ions are known to arise with high kinetic energy in dissociative attachment to isolated CF4.