Photoionization mass spectrometric study and ab initio calculations of ionization and bonding in P--H compounds; heats of formation, bond energies, and the 3B1--1A1 separation in PH+2

The ion yield curves of PH+3, PH+2, and PH+ from photoionization of PH3 have been measured. The free radical PH2 has been generated by pyrolysis, and the ion yield curve of PH+2 (PH2) determined. These measurements yield directly I.P. (PH3) = 9.870 +- 0.002 eV, and I.P. (PH2) = 9.824 +- 0.002 eV. In addition, we deduce D0 (H2P--H) = 82.46 +- 0.46 kcal/mol, D0 (HP--H) = 74.2 +- 2 kcal/mol, D0 (P--H) = 70.5 +- 2 kcal/mol, I.P. (PH) = 10.18 +- 0.1 eV, and other thermochemically related quantities. The ionization energies of PH, PH2, and PH3 are computed by ab initio molecular orbital methods to fourth order in Moller--Plesset theory, and are found to be in good agreement with experiment. The ground state of PH+2 is inferred to be 1A1, with the 3B1 state higher by > or =0.71 eV. This ordering is the reverse of that in CH2 and NH+2