Interpretation of the Appearance Potentials of Secondary Ions

Abstract

The statistical theory of mass spectra assumes that the excitation energy in a molecule-ion is essentially equipartitioned prior to unimolecular decomposition. Some of the consequences of this assumption have been deduced and the results have been used in interpreting the observed appearance potentials of secondary and tertiary ions of neopentane, n-butane, and 1-butene. Although the results are not quantitative, it is evident that considerable vibrational energy is removed with the neutral fragment. The problem of the detailed interpretation of appearance potentials is complicated by the fluctuation of the vibrational energy distribution in the products of a decomposition from the most probable value, i.e., equipartition. Some general considerations with regard to determination of minimum-energy decomposition paths and the significance of this study in relation to the statistical theory of mass spectra are also presented.