Single-Center Single-Determinant Calculation of the Relative Energies of CH3+, CH3, CH4, and CH5+. The Proton Affinity of Methane

Using one-center single-determinant approximations to the pertinent wave functions, the energies of CH3, CH3+, and CH5+ relative to CH4 have been calculated. If corrections for the different molecular geometries of the various species are made, reasonably good agreement with experiment for the carbon—hydrogen bond strength in methane, the ionization potential of CH3, and the appearance potential of CH3+ from CH4 is obtained. The modification of the calculation that gives the best agreement with experiment for these three known quantities leads to a value of 7.26 eV for the proton affinity of methane.