A further study on the electronic structure and spectrum of ethylene

Abstract

Calculations on the lower electronic states, ionization potential and electron affinity of ethylene are carried out by a semi-empirical ASMO method including configuration interaction. The carbon-carbon sigma bonding electrons are explicitly included. One-centre quantities for ethylene, ethylene negative ion and ethylene positive ion are evaluated from atomic valence-state energies, taking account of changes in effective nuclear charges of the corresponding states. Two-centre electronic repulsion integrals are determined by interpolation between theoretical values for distant nuclear separations and one-centre repulsion integrals obtained; two-centre core integrals are computed purely theoretically. Good agreement between calculated and observed values is obtained. Although preferential stabilization of the ion cannot be expected from sigma-pi configuration interaction, it is shown that the reorganization of the electronic sub-structure of the atom upon ionization plays a significant role.