Theory of Electronic Excitation and Reorganization in the Formaldehyde Molecule

Abstract

The use of a previously described iterative method of separated electron pairs is demonstrated by calculations on the formaldehyde molecule. Investigation is made, for example, of detailed changes in the polarity of sigma bonding electron wave functions in this molecule when a pi or lone-pair electron is excited or ionized. The molecule is treated as a six-electron problem (four electrons in the C=O bond plus two lone-pair electrons on O); matrix elements involving the ``core'' are obtained by fitting experimental data. The use of Pariser-type one-center repulsion integrals is tested in conjunction with various sets of two-center repulsion integrals. Although one combination gives reasonable results, none of the combinations is found to be entirely satisfactory, and a procedure is outlined from which could be obtained one-center integrals approximately incorporating Arai-Hurley type corrections. It is demonstrated (with reservations) that the constant sigma structure assumption, usually made in calculations of pi electron excitations and ionizations, is not always good with regard to wave functions, but that it may lead to only small errors in calculated energies.