CNDO–SCF–CI Calculations of the Excited Electronic States of 1,3-Butadiene

Abstract

Energies of low-lying excited states of s-cis and s-trans 1,3-butadiene have been calculated using the CNDO–SCF method of Pople, Santry, and Segal, with the inclusion of configuration interaction among the single electron excitations. The results are shown to agree well with available experimental values. An extensive comparison is made between CNDO–SCF and recent ab initio SCF orbital and excitation energies and also excited state energies resulting from CI treatments of the excited configurations of the two theoretical methods. Results obtained from an earlier semiempirical pi-electron calculation are also included for comparison. Charge redistribution in some CNDO excited configurations is investigated.