Effect of temperature on the dissociative electron attachment to CClF3 and C2F6 a)

Abstract

The total electron attachment rate constant ka(〈ε〉) for CClF3 and C2F6 has been meausured using an electron swarm technique in the mean electron energy range 0.41 to 4.81 eV and over the range of temperature T from 300 to 750 K. At each value of T the total electron attachment cross section σa(ε) was determined from the measured ka(〈ε〉) using the swarm unfolding technique and was compared with the results of a mass spectrometric study. The σa(ε) for C2F6 shows a single peak (due to F− and CF3−) which shifts from 3.9 eV at 300 K to ∼3.3 eV at 750 K. (The onset shifts correspondingly from 2.3 to 1.5 eV.) For CClF3 the σa(ε) shows two peaks: at ∼1.5 eV (due to Cl−) and at ∼4.7 eV (due to Cl−, F−, CClF2−, and ClF−). The peak at ∼1.5 eV is especially sensitive to changes in T. The peak value of σa(ε) increased by a factor of ∼3, and the energy position of the peak and onset shifted to progressively lower energies when T increased from 300 to 700 K. The analysis of these results led us to conclude that the changes in ka(〈ε〉) and σa(ε) for the dissociative attachment processes of these molecules with increasing T result from the increase with T of the total internal (≂ vibrational) energy of the molecule.