Negative Ion Formation in Hydrogen Chloride by Electron Impact

Abstract

The energy dependence for the formation of Cl— from HCl vapor by dissociative attachment of electrons is studied with a mass spectrometer. Within experimental error the low-energy onset for the capture process occurs at the same energy as that for the maximum capture cross section which is determined to be at 0.66 ev. The ion pair formation process, HCl+e→H++Cl—, is found to have a linear onset at 14.5 ev. The maximum yield of negative ions by this process is found to be only a few percent of that from the low-energy capture process. The energy distribution of the electron beam and the calibration of the energy scale is obtained by comparison with SF6—. It is observed that when a low-energy electron capture process is possible, spurious effects may be obtained at higher electron energies due to low-energy secondary electrons ejected from electrode surfaces by the primary beam.