Lower Electronic Levels of the Radicals PH and PH2

This paper describes a semiempirical quantitative theory of the low-lying electronic states of the radicals PH and PH2. The method is an extension of that developed by Jordan and Longuet-Higgins to treat Row II hydrides. It indicates that a small percentage of d character in the valence state may have a considerable effect on the equilibrium bond angle, if the d orbital is somewhat contracted by polarization. Including this effect, the results are in excellent agreement with experiment: PH2 in its excited 2A1 state is found to be strongly bent; PH3 is predicted to have an inversion barrier of 34.5 kcal/mole.