Negative ion formation in collisions between potassium and fluoro- and chloromethanes: Electron affinities and bond dissociation energies

Abstract

A potassium atom beam in the energy range 1–30 eV was used to study the formation of negative ions in electron transfer collisions with the halogenated methane molecules CF 4, CF 2Cl 2, CHCl 3, CFCl 3 and CCl 4. For the first time the parent negative ions CCl 4, CFCl 3 and CF 2Cl 2 have been mass spectrometrically detected and from the translational energy thresholds the following electron affinities were determined: EA(CCl 4) = 2.0 ± 0.2 eV, EA(CFCl 3) = 1.1 ± 0.3 eV and EA(CF 2Cl 2) = 0.4 ± 0.3 eV. These results are compared with semi-empirically determined potential energy curves by Wentworth, George and Keith. In addition, the measurement of fragmentation products of the halogenated methanes allowed the determination of their electron affinities and bond dissociation energies.