EFFECTIVE INTERMOLECULAR RELAXATION IN (C6F6)(N)(-)CLUSTERS - MECHANISM OF C(6)F(6)(-)FORMATION ON LOW-ENERGY-ELECTRON IMPACT

Electron attachment to C6F6 molecules and clusters is studied in a beam experiment in the energy range 0-8 eV. In single molecules, a long-lived parent anion C6F6- is observed within a narrow peak near 0 eV. In clusters, a comparatively broader attachment feature yielding the monomeric anion C6F6- and the larger cluster ions (C6F6)(n)(-) is observed with a peak maximum distinctly above 0 eV. The present results indicate that the narrow width of the attachment peak in isolated molecules is essentially controlled by the autodetachment lifetime of the transient anion and hence by the observation time window of the experiment. In clusters, intermolecular stabilization processes strongly compete with autodetachment, resulting in an attachment profile which mirrors the primary shape of the C6F6- resonance. In addition to the low energy process, C6F6- (and the products (C6F6)(n)(-)) are generated from clusters with considerable intensity also at energies above 3 eV. The associated energy profiles strongly suggest that these ions are formed via inelastic scattering by one molecule and capture of the slow electron by another molecule of the same cluster (autoscavenging). The present results are compared with previous electron transmission experiments on gaseous C6F6 and discussed in terms of the molecular orbitals involved.