Study of the Electronic Structure of Molecules. XVI. Analysis of the Formation of the Methane Molecule in the Hartree-Fock Model

Abstract

The energy of formation for the methane molecule (in the Hartree-Fock approximation) is analyzed by (1) building up the electronic configuration starting from the nuclear field and adding one pair of electrons at a time; (2) by variation of the C-H distances; (3) by removing a single electron from each orbital (single ionization). The energy and electronic densities for CH48+, CH46+, CH44+, CH42+, CH4+, and CH4are discussed using two methods. The first technique uses Hartree-Fock atomic data and a very simple physical model (requiring essentially no computations). With this method, the total energies and the orbital energies of CH48+, CH46+, and CH44+ are computed to about the same accuracy as obtained from the Hartree-Fock molecular computations (the second technique). The Hartree-Fock energies are analyzed with the bond energy analysis technique, and the HartreeFock densities are analyzed with the electron population analysis technique. The study of the ionization potentials of a single electron (from each of the occupied orbitals) brings about a clear indication of the large amount of reorganization which follows ionization. This effect was pointed out in paper VI of this series for valency electron; it is now stressed for inner shell electrons. It is noted that the 100% agreement between the computed and the experimental ionization potential for the inner shell indicates that the correlation corrections are affected by the rearrangement to about the same per cent as the Hartree-Fock energies. A discussion on the hybridization for methane would predict (in a Hartree-Fock model) a s2p2 hybridization; however, mainly because of charge-transfer effects, the hybridization is about s15p2 6; clearly, the hybridization is a function of the C-H distance and of the degree of ionization of the species (and these effects are discussed). © 1972, American Chemical Society. All rights reserved.