Low energy (0–15 eV) electron stimulated reactions in single 1,2-C2F4Cl2 molecules and clusters

Abstract

Formation of negative ions following electron impact to single gas phase C2F4Cl2 molecules and to homogeneous C2F4Cl2 clusters is studied in crossed beam experiments with mass spectrometric detection of the ionic products. From single molecules a variety of fragment ions are observed arising from dissociative electron attachment (DA) via two low energy resonances located near 0.3 and 2.5eV. The most abundant product is Cl− with an estimated DA cross-section of (2±1)×10−15cm2. On a comparatively weaker scale the ions F−, Cl2−, CClF2−, C2ClF4−, and ClF− are observed, with the ion yields all characterized by pronounced resonance profiles. A further very weak and diffuse feature associated with negative ion formation appears in the energy range 8–14eV. Electron attachment to clusters additionally generates the undissociated complexes Mn− (M=C2F4Cl2) including the stabilized monomer anion, and solvated ions of the form Cl−·Mn. The undissociated complexes Mn− are considerably more abundant than the solvated ions. This mirrors the reaction pathway on an early time scale (femtoseconds to picoseconds) after electron localization in the target cluster indicating that stabilization is preferred over dissociation. The present gas phase and cluster experiments are discussed in relation to recent experiments on electron stimulated desorption and synthesis of Cl2 from condensed C2F4Cl2[8].