ANION FORMATION FROM GASEOUS AND CONDENSED CF3I ON LOW-ENERGY-ELECTRON IMPACT

Anion formation following electron impact to CF3I is studied in the energy range 0-15 eV. The experiments include gas phase CF3I in the effusive molecular beam under single collision conditions, clusters in a supersonic molecular jet and CF3I condensed in the UHV in multilayer amounts onto a cold metallic substrate. In isolated molecules fragment anions are formed via dissociative attachment (DA) and dipolar dissociation (DD). The DA resonances are located at 0.0 and 3.8 eV and are assigned as single particle and two particle resonance, respectively. The low energy resonance exhibits an exceedingly high cross section for I-formation, while the higher energy resonance decomposes into CF3-, F-, and FI- with comparatively low intensity. Both resonances possess significant C-I antibonding character as apparent from their decomposition dynamics. In clusters the stabilized molecular anion CF3I- and larger complexes of the form (CF3I)n- and (CF3I)n.I- are observed. At higher energies anion formation is affected by inelastic scattering from one molecule and capture of the slow electron by a second molecule within one cluster (self-scavenging). Scavenging features in clusters and in isolated molecules beyond single collision conditions are compared. Electron stimulated desorption (ESD) is dominated by CF3- which is generated via DA from the core excited resonance with its strong F3C-I antibonding nature.