Computational Studies of Open-Shell Phosphorus Oxyacids. 1. P-H Bond Homolysis in H₂PO₂

The hypothetical molecule dihydrodioxophosphoranyl (1) has been studied computationally. Both 3-21G^(⋆) and 6-31G^⋆ unrestricted Hartree-Fock (UHF) wave functions exhibited inherent doublet instability which was corrected for by consideration of correlation effects. Configuration interaction proved most effective in this respect, while Mϕller-Plesset perturbational corrections were fair when extended to third order and only marginal when truncated at second order. The barrier to P-H bond homolysis was determined to be 4.8 ± 0.3 kcal/mol. The metastability of 1 has been explained in the formalism of valence bond theory. It arises from interactions of degenerate valence bond functions corresponding to reactants and products with an intermediate configuration corresponding to a n ⟶π^⋆ (1A₂⟶3B₁) excited state. Predicted spectral data to aid in the identification of 1 are presented.