Comparison of the electronic spin-orbit splitting in CH₃O using UHF and RHF wavefunctions

Abstract

The electronic spin-orbit splitting λ_e of methoxy was calculated using RHF wavefunctions and a semiempirical spin-orbit hamiltonian. The result, λ_e = -158 cm^-1, agrees well with a calculation that used a RHF wavefunction and the relativistic Breit hamiltonian (λ_e = -142 cm^-1). However, this result does not agree with a calculation that used the same semiempirical spin-orbit hamiltonian and an UHF wavefunction (λ_e = -78 cm^-1). The disagreement arises from the form of the UHF and RHF wavefunctions. The experimental evidence is not sufficiently conclusive for one to decide which wavefunction gives a better description of methoxy.