Structures, thermochemistry, and electron affinities of the PFn and PF−n series, n=1–6

Abstract

A quantum mechanical study of the phosphorus fluorides and their singly charged anions was carried out. A range of density functional methods was used. Optimized geometries, adiabatic electron affinities, vertical electron affinities, vertical detachment energies, and stabilities toward the loss of a single fluorine atom or fluorine ion are reported. These properties were evaluated exhaustively using four exchange-correlation functionals: Becke’s 1988 exchange functional with the correlation functional of Lee, Yang, and Parr, Becke’s 1988 exchange functional with the 1986 correlation functional of Perdew, Becke’s three parameter Hartree–Fock/density functional hybrid exchange functional with the correlation functional of Lee, Yang, and Parr and Becke’s half-and-half Hartree–Fock/density functional hybrid exchange functional with the correlation functional of Lee, Yang, and Parr (BHLYP). These exchange-correlation functionals were used in conjunction with a double-ζ plus polarization basis and a double-ζ plus polarization basis set which was augmented with an even tempered set of s and p diffuse functions. Less complete examinations of the local spin density approximation, Becke’s 1988 exchange functional with the 1991 correlation functional of Perdew and Wang are also reported. Results were compared to the limited experimental data to see which combination of functional and basis set, if any, reproduced known results and could be expected to make accurate predictions where experimental data is absent. This comparison shows that the BHLYP exchange-correlation functional reproduces the known experimental geometrical parameters quite well. From work on related systems, the BHLYP method appears to predict the most reliable molecular electron affinities. With the double-ζ plus polarization basis set augmented with s and p diffuse functions, the predicted BHLYP adiabatic electron affinities are 0.71 eV (PF), 0.75 eV (PF2), 0 (PF3), 3.17 eV (PF4), and 1.25 eV (PF5). These theoretical electron affinities are expected to lie somewhat above the true values. The PF6 molecule is predicted to be dissociative with respect to PF5 and F, but PF−6 is significantly bound with respect to either PF5+F− or PF−5+F.