Ionization Potentials and Autoionization Levels of Methyl, Ethyl, n-Propyl, and n-Butyl Free Radicals by an Energy-Calibrated Molecular Orbital Method

Abstract

Ionization potentials and possible autoionization levels of the methyl, ethyl, n-propyl, and n-butyl free radicals have been calculated with an energy-calibrated molecular orbital method. Molecular orbitals were constructed as a linear combination of 1s hydrogen and 2p carbon atomic orbitals. Autoionization levels were calculated from molecular orbitals constructed to include autoionizing levels of the carbon atom (2p3, 1D, etc.). Two different models of the free radicals were formulated for the calculations, a simple planar model in which the interaction of the atomic orbitals was restricted to adjacent atoms, and a more complicated group model in which the interactions of the orbitals were much less restricted. Calculations in both models were based upon the assumption that the ionization processes are principally controlled by the unpaired carbon 2p electron. Calculated and experimental values are in reasonable agreement over the energy range of the experimental data. The lowest ionization potential of the n-butyl radical is calculated to be lower than the experimental value (8.0 vs 8.6 eV).