Ab initiocalculation of the first ionization potential in linear alkanes using exciton theory

Abstract
An ab initio calculation is used to give the form of the ionization potential in the alkane series and to explain the origin of the various contributions to this potential. The question of whether the ionization relates to a σ-type orbital, composed mainly of carbon atomic orbitals, or to a π-type, composed of CH bonds, is considered. The results show a gradual evolution from a CH ionization (13·26 eV) in CH4 to a CC ionization (10·0 eV) at the farthest limit of the series.