Molecular orbitals of methane: symmetry or hybridization?

Abstract

Orbital electron density distributions and momentum distributions of both core and valence space of methane are studied quantum mechanically, using RHF/TZVP and B3LYP/TZVP models, respectively. The three molecular orbitals (MOs) of methane in the ground electronic state (X1A1), namely, the core MO, 1a1 and the valence MOs, i.e. 2a1 and three-fold energy degenerate MOs 1t2, are studied in both coordinate space and momentum space. They are compared with the corresponding atomic orbitals (AOs) of a ‘free’ carbon atom in its ground electronic state (3P) using configuration averaged unrestricted HF (UHF) method. The electronic structure of methane inherits that of a free single carbon atom, indicating that the symmetry of methane contributes to the equivalent orbitals and their behavior. There are no any quantitative evidences of hybridization for the MOs of methane in either coordinate space or momentum space. The core MO (1a1) of methane in momentum space is found to be nearly indistinguishable to the core AO (1s) of a free carbon atom using the same model. The net chemical bonding results as displayed in the valence MO momentum distributions have clearly retained the orbital wave function anisotropy as s-like and p-like in both methane and the free carbon atom.