Electron attachment to chlorofluoromethanes using the electron-swarm method

Abstract

Electron attachment rate constants, as a function of pressure-reduced electric field, were measured in mixtures with nitrogen for CCl3F, CCl2F2, and CClF3 using the electron swarm method. From these data total electron attachment cross sections σa(ε) as a function of electron energy ε were determined for the chlorofluoromethanes using the electron-swarm unfolding technique and a new set of electron energy distribution functions for N2. For CCl3F and CCl2F2 three maxima in σa(ε) were found at thermal energy, 0.25 and 0.75 eV and at 0.07, 0.30, and 0.93 eV, respectively. Only one pronounced maximum in σa(ε) for CClF3 was observed at 1.4 eV. The thermal values of the attachment rate constant for CCl3F, CCl2F2, and CClF3 are, respectively, 3.90×108, 4.00×107, and 6.05×103 sec−1 Torr−1. Additionally, comparisons are made between the σa(ε) calculated for these and other molecules using both the new electron energy distribution functions for N2 and those determined earlier. Substituent effects on the number and position of negative ion states and on the magnitude of σa(ε) for the chlorofluoromethanes are discussed.