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.

Absolute and effective cross-sections for low-energy electron-scattering processes within condensed matter

“…Clearly, the electron trapping processes (i.e., DEA, RS, and IMS) are greatly affected by the change in local environment associated with the change in phase. This sensitivity to the local environment was investigated further by varying the thickness of the supporting Kr film in CT experiments for CH 3 Cl [41,43], CH 3 Br [43], and CFCl 3 [47]. As illustrated in Fig.…”

Dissociative electron attachment to bromotrifluoromethane

“…A more recent literature review is given by Bjarnason et al in 2012 [4] and recently dissociative electron attachment (DEA) to CF 4 has also been studied by the means of velocity slice imaging (VSI) [5,6]. Studies on the chlorinated congener are more fragmented and the initial DEA studies on CF 3 Cl were conducted by Illenberger et al [7][8][9] and by Underwood-Lemons et al [10]. More recent work on low-energy electron interaction with CF 3 Cl includes a study on elastic electron scattering [11] and an evaluation of the total scattering crosssection [12] as well as theoretical and experimental studies on dissociative electron attachment [13][14][15].…”

Photon-stimulated desorption of F− ions from CF3Cl adsorbed on Si(111)-7×7

“…This feature was attributed to an excited resonance resulting in a precursor (CF 3 Cl)* Ϫ ion which then followed by sequential dissociation with the cleavage of a C-F bond and leaving an electronically excited (CF 2 Cl)* Ϫ fragment as the first step [57][58][59] ͑ CF 3 Cl͒* Ϫ ͑ 4.1 eV͒→͑CF 2 Cl͒* Ϫ ϩF ͑DA: step 1).…”

“…The electronically excited (CF 2 Cl)* Ϫ may further decay according to 57,59 ͑ CF 2 Cl͒* Ϫ →CFClϩF Ϫ ͑ DA: step 2 ͒.…”