HeI photoelectron spectra of PH 2 and PF 2: comparison between simulation and experiment

Abstract

Molecular orbital calculations on PH 2 and PF 2 and some of their low-lying cationic states, followed by Franck-Condon calculations, have been performed with the objective of simulating HeI photoelectron band of these radicals. The molecular orbital calculations involved MP2 and CCSD(T) geometry optimization and frequency calculations, with basis sets of size up to 6-311G(3df,2p), and as well as G1/G2 calculations. Franck-Condon simulations of photoelectron bands were performed using force constants derived from the ab initio calculations. Based on comparison between simulated and observed spectra, the first adiabatic ionization energy of PH 2 has been confirmed as (9.84 ± 0.01) eV and the lowest singlet-triplet separation in PH 2 + ( 1 A 1 − 3 B 1 has been deduced as (0.78 ± 0.04) eV. Also, the first adiabatic ionization energy of PF 2, corresponding to the ionization PF 2 + 1 A 2 ← PF 2 X 2 B 1 , has been established as (8.84 ± 0.01) eV. The vibrational structure observed in the first band of PF 2 has been assigned to excitation of the symmetric stretching mode ( v 1) in PH 2 in PF 2 +(X 1A 1) and the vibrational structure observed in the second band of PH 2 has been assigned to excitation of the deformation mode ( v 2) in PH 2 +(a 3B 1).