Negative ion resonances in CF4 probed by dissociative electron attachment

Abstract

An electrostatic impact spectrometer is used to measure, between 3 and 10 eV, the kinetic energy, the angular distributions and the yield of negative fragment ions formed by dissociative attachment in CF4. The energy range and the symmetry of the resonances are determined as well as the dissociation processes and their dynamics. The first resonance state, observed around 6.8 eV, is attributed to the CF4- 3T2 shape resonance adiabatically dissociating in the two channels F-+CF3 and CF3-+F. The excess energy is shared between the fragment kinetic energies and the internal (vibrational) excitation of the trifluoromethyl fragment. The next resonance, located around 8 eV, is assumed to be of T1 symmetry. The authors suggest that this Feshbach resonance dissociates in F- ions by the sequential breaking of two C-F bonds through an intermediate CF3-* electronically excited negative molecular ion. The 2A1 shape resonance has not been observed in the dissociative channel.