CNDO Molecular-Orbital Theory of Molecular Spectra. I. The Virtual-Orbital Approximation to Excited States

A semiempirical theory of transition energies and molecular excited-state geometries is developed. The excited-state electronic wavefunction is approximated by a single determinant constructed using a virtual orbital obtained from the minimization of the energy of the ground-state electron configuration. This theory represents a semiquantitative study of the accepted qualitative description of molecular spectra. Results are presented for HNO, …