Electron attachment to CF3Cl and CH3Cl on the surface and in the bulk of solid Kr

Abstract

The formation of stable anions induced by the impact of 0–1.6 eV electrons on CF3Cl and CH3Cl condensed at the surface, and embedded within the bulk of solid Kr is investigated by measuring charging of the doped Kr films. Effects of the Pt substrate and under- and over-layer coverage of these molecules on the dissociative electron attachment and stable anion formation (SAF) are studied in detail by varying the film thickness and the position of the molecules within the film. Due to recent advances, we provide new and more reliable values of the absolute cross sections, σSAF, for SAF. σSAF reaches a maximum of 2.1×10−16 cm2 at 0.6 eV for CF3Cl embedded in solid Kr; for CH3Cl, this maximum is ∼10−16 cm2 at 0.2 eV. These values correspond to an enhancement of factors of 5 and 10, respectively, relative to σSAF measured at the surface. The electron energy dependence of σSAF is also evaluated theoretically from calculations performed with the R-matrix formalism extended to include the influence of condensed-matter environments. By incorporating into the theory the band structure of the solid and different values of the polarization induced into the medium by electron capture, we study the effect of these parameters on σSAF. Comparison between experimental and theoretical σSAF’s allows us to analyze the gas-phase parameters that must be modified to generate condensed-phase cross sections from gas-phase data and to discuss the effect of phenomena which are absent in the gas-phase (e.g., caging).