High resolution studies of dissociative electron attachment to molecules: dependence on electron and vibrational energy

• Published in: Journal of physics. Conference series Vol. 88; no. 1; p. 012013
• Main Authors: Ruf, M-W, Braun, M, Marienfeld, S, Fabrikant, I I, Hotop, H
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.11.2007
• Subjects: Activation energy; Cross-sections; Electron attachment; Electron energy; Electron swarms; Energy; Lasers; Methyl bromide; Photoelectrons; Physics; Plasma processing; Potential energy
• ISSN: 1742-6596; 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/88/1/012013

For several molecules which are important for plasma processing and gaseous dielectrics (CF3I, CF3Br, CH3Br, and SF6), we have studied the dependence of dissociative electron attachment (DEA) on both the electron energy and on the initial vibrational energy. With reference to electron swarm data, we determine highly-resolved absolute DEA cross sections over a broad energy range, using the Laser Photoelectron Attachment (LPA) method (E 0–0.2 eV, δE ≈ 1–3 meV) and the EXtended Laser Photoelectron Attachment (EXLPA) method (0–2 eV, δE ≈ 15–30 meV). The experimental data are compared with the results of R-matrix calculations, involving ab initioinformation on the potential energy curves and semiempirical autodetachment widths. For CF3I and CF3Br, previous DEA cross sections are found to be substantially too high. For CH3Br, the measurements confirm a predicted vibrational Feshbach resonance, associated with the v3 4 vibrational threshold, and the value of the activation energy (due to an intermediate barrier) for this exothermic DEA process. For SF6, we report absolute cross sections for SF6− as well as SF5− formation for vibrational temperatures ranging from 200 to 500 K. Moreover, the first absoluteDEA cross sections (SF5− formation) for CO2-laser excited SF6 molecules have been obtained at different initial vibrational temperatures. The results indicate that the effect of the mode-selective energy input into the v3-mode (predominantly v3 1) on the enhancement of SF5− formation is very similar to that of a corresponding rise of the average vibrational energy by thermal heating; at E 2 meV electron energy, the results indicate an activation energy of about 0.38 eV.