Theoretical prediction of the singlet-triplet intercombination separations for NH, OH⁺, PH, and SH⁺

The singlet–triplet (a 1 Δ–X 3 Σ − ) intercombination separations for NH, OH + , PH, and SH + are predicted to be 1.63, 2.19, 0.95, and 1.16 eV, respectively. These predictions are expected to be good to ~0.1 eV and are based on a quantitative model of the relationship of the united atom and the diatomic hydride, AH. The intercombination separations as calculated via Hartree–Fock energies are corrected for the "change in correlation energy" involved in the transition making use of united-atom changes in the correlation energy.