Energy balance in dissociative electron attachment to C2F5I

Abstract

Partitioning of excess energy in the unimolecular decomposition of C₂F₅I⁻ anions generated by free electron attachment is studied by means of a time-of-flight (TOF) analysis of the fragment negative ions. At very low electron energies selective bond cleavage generating I⁻ and C₂F₅ occurs via an intense and narrow resonance located near 0 eV. In the energy range between 2 and 6 eV further resonant structures appear yielding F⁻ and I⁻. The low energy resonance decomposes impulsively by direct electronic dissociation along the ground state potential energy surface. The translational energy distribution is quasi discrete carrying 66% of the available total excess energy. Using a classical model calculation treating the C₂F₅ radical as a rigid rotor we predict that out of the 34% of excess energy remaining as internal energy in the neutral fragment (C₂F₅) 19% appears as vibrational energy and 15% as rotational energy. In contrast to the low energy ion state, the excited resonances decompose less directly resulting in quasi thermal distributions for the translational excess energy.