HEI PHOTOELECTRON-SPECTRA OF PH2 AND PF2 - COMPARISON BETWEEN SIMULATION AND EXPERIMENT

Molecular orbital calculations on PH2 and PF2 and some of their low-ly ing cationic states, followed by Franck-Condon calculations, have been performed with the objective of simulating HeI photoelectron bands of these radicals. The molecular orbital calculations involved MP2 and C CSD(T) geometry optimization and frequency calculations, with basis se ts of size up to 6-311G(3df,2p), and as well as G1/G2 calculations. Fr anck-Condon simulations of photoelectron bands were performed using fo rce constants derived from the ab initio calculations. Based on compar ison between simulated and observed spectra, the first adiabatic ioniz ation energy of PH2 has been confirmed as (9.84 +/- 0.01) eV and the l owest singlet-triplet separation in PH2+ ((1)A(1)-B-3(1)) has been ded uced as (0.78 +/- 0.04) eV. Also, the first adiabatic ionization energ y of PF2, corresponding to the ionization PF(2)(+ 1)A(1) <-- PF2 (XB1) -B-2, has been established as (8.84 +/- 0.01) eV. The vibrational stru cture observed in the first band of PF2 has been assigned to excitatio n of the symmetric stretching mode (v(1)) in PF2+(X(1)A(1)) and the vi brational structure observed in the second band of PH2 has been assign ed to excitation of the deformation mode (v(2)) in PH2+(a(3)B(1)). (C) 1997 Elsevier Science B.V.