Dissociative electron attachment to CF2Cl2 using a high-resolution crossed-beams technique

Using a crossed electron-molecule beam ion source in combination with a quadrupole mass spectrometer we have studied the electron energy dependence of the dissociative attachment process CCl2F2 + e(-) --> Cl- (at electron energies from about 0-2 eV and with an energy resolution of about 60 meV) in a target gas range of about 300-420 K. Utilizing the improved energy resolution of the present experimental set-up it was possible to determine the accurate shape and magnitude of the cross section function in this low-energy range. This leads to the conclusion that close to 0 eV energy (below about 0.15 eV) the reaction proceeds via s-wave capture, whereas at higher energy (above 1 eV) autodetachment significantly determines the shape of the cross section. Moreover, the present measurements allow us to clarify previously reported differences in the absolute cross section, in the number of peaks and in the energy positions of these peaks. Finally, by analysing the measured strong temperature dependence of the cross section peak at about zero electron energy the activation barrier for this dissociative attachment was determined to be 120 +/- 20 meV in good agreement with thermochemical data deduced from swarm experiments.