Electron-attachment spectroscopy: formation and dissociation of negative ions in the fluorochloroethylenes

Abstract

The formation and dissociation of negative ions in C 2Cl 4, C 2FCl 3, 1,1-C 2F 2Cl 2, 1,2-C 2F 2Cl 2 (isomeric mixture), C 2F 3Cl and C 2F 4 have been studied employing (dissociative) electron-attachment spectroscopy with nearly monoenergetic electrons in the energy range 0–15 eV. All six compounds show low-lying resonances (below 4eV) associated with various dissociation channels leading to one negative and one neutral fragment. It is found that the resonance energy increases if Cl is replaced by F. Electron affinities in the limit of the unknown excess energy are given for the radicals C 2Cl 3, C 2F 2Cl 2, C 2F 2Cl and C 2F 3. For C 2Cl 4 and C 2F 2Cl 2 long-lived parent molecular anions are observed. Only tetrafluoroethylene gives fragments by cleavage of the double bond, as a result of the perfluoro effect.