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Molecular Dissociation by Electron Bombardment: A Study of Si
Phys. Rev. 71, 93 – Published 15 January, 1947
DOI: https://doi.org/10.1103/PhysRev.71.93
Abstract
The first part of this paper deals with molecular dissociation in general, with reference to the determination of appearance potentials of molecular fragments. Appearance potentials are generally determined from plots of ion current versus electron energy by either of two methods: determination of the energy at which ion current is first detected; or location of the intercept with the energy axis of the extrapolation of the straight line portion of the ionization efficiency curve. It is pointed out that the first procedure has a rather indefinite relation to the physical quantities involved and that the value obtained by the second method corresponds quite closely to the energy necessary to produce a transition through the center of the Franck-Condon region. The last section of the paper contains an analysis of data obtained in a study of the dissociation of silicon tetrachloride. Both positive and negative ions are formed in processes resulting in most of the possible configurations. The data are correlated with values of dissociation energies from external data, and estimates are made of the ionization energies of the radicals involved. Ionization energies of Si and Si are measured directly and are found to be 11.6±0.2 volts and 11.8±0.3 volts, respectively.
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