Valence-bond studies on CH₄

Abstract

Valence-bond calculations using a minimal Slater basis set are reported for the ¹ A ₁ ground state of CH₄. The energies obtained with various natural atomic orbital configurations are compared. The most important configuration is 1s² 2s2p _x 2p _y 2p _z h ₁ h ₂ h ₃ h ₄. Perfect-pairing approximation calculations using hybrid orbitals are described. The most important hybrid orbital configuration is that in which the carbon atom carries a negative charge. For the covalent perfect-pairing wavefunction the effect of varying the hybridization is investigated. The valence-state configuration is approximately s^1·7 p^2·3. Calculations using orbitals in which the hybrid atomic orbitals can be distorted by the inclusion of the orbital with which it is paired are also reported. From these calculations an estimate of the energies of the ³ A ₁ and ³ T ₂ excited states is obtained.