ENERGY COMPONENT ANALYSIS OF THE JAHN-TELLER EFFECT IN THE METHANE RADICAL CATION

Extensive configuration-interaction calculations with double-zeta plus polarization and near triple-zeta plus polarization basis sets are used to analyze the Jahn-Teller (JT) effect in the methane radical cation. Energy component analysis shows that the Jahn-Teller effect leads to a decrease in the expectation value of the electron-nuclear attraction energy, an increase in the expectation value of the interelectronic repulsion energy, and an increase in the internuclear repulsion energy. These observations are consistent with a contraction of the electron cloud. The dominant factor in the -0.0550 hartree Jahn-Teller distortion (T(d) --> C2-upsilon) in CH4+ is the -0.5262 hartree change in the electron-nuclear attraction energy. The differences in all energy components are large in relation to the JT distortion. Interelectronic repulsion plays a dominant role in determining the relative energies of the possible JT distorted structures, but electron correlation effects are relatively unimportant.