Dissociative Electron Attachment to Gas- and Condensed-Phase CF3Cl: Anion Desorption and Trapping

Abstract

The interaction of electrons in the energy range from near zero to 10 eV with CF3Cl physisorbed on a Kr surface is studied and compared with previous gas-phase experiments on isolated molecules and CF3Cl clusters. In the gas phase CF3Cl shows resonances in the dissociative attachment (DA) cross section at 1.4 eV, near 4−5 eV, and at 9 eV with the 1.4 eV feature assigned as a single particle resonance with a strong C−Cl repulsive nature. From adsorbed CF3Cl, we observe desorption of Cl- and F- with resonances in the cross section which can be correlated to the gas-phase DA features. Despite its antibonding nature, Cl- desorption via the single particle resonance is very weak, indicating that direct desorption processes do not occur; i.e., orientations of the molecule with the C−Cl axis pointing away from the surface can be excluded, and desorption is always preceded by postdissociation interactions. Charge trapping is virtually restricted to the low-energy resonance. Its maximum is at 0.8 eV and reflects the energy shift of the transient ion due to solvation. The absolute trapping cross section is 43 × 10-18 cm2, exceeding the gas-phase DA value by about 1 order of magnitude. The behavior of the low-energy resonance is described in terms of one-dimensional potential energy curves previously used to model temperature effects in DA to gas-phase CF3Cl, with the anionic curve shifted by the solvation energy. It is shown that autodetachment, which is by far the dominant decay channel in the gas phase, is substantially suppressed in the condensed phase.