Reactions in acetone, perfluoroacetone and acetylene triggered by low energy (0–15 eV) electrons

Abstract

Dissociative electron attachment (DEA) to acetone (CH3COCH3), perfluoroacetone (CF3COCF3) and acetylene (HCCH) is studied in the gas phase under collision-free conditions. The results are compared with those recently obtained from a study on electron attachment to homogeneous clusters of acetone and perfluoroacetone (Martin et al., 2009). Gas phase acetone and perfluoroacetone show a series of DEA resonances extending over a wide energy range and leading to various fragment ions. Perfluoroacetone additionally shows a strong signal due to the formation of the parent anion close to zero energy. In strong contrast to that, the cluster analogues exhibit only a low energy resonance while fragmentation is strongly suppressed. Such behaviour mirrors the intrinsic decomposition mechanisms which proceeds rather via predissociation involving a loose transition state than by direct dissociation along repulsive potential energy surfaces. This picture is confirmed by a time-of-flight (TOF) analysis of the fragment ions from the isolated compounds revealing that all fragment ions are formed with only low translational energy. DEA to acetylene leads to C2H− and C2− arising from different resonance regions, with C2H− as the prominent signal at 3eV resulting from predissociation of the π* resonance.