Quantum-Chemical Study of Some Pnicogen Monofluorides

A quantum‐chemical investigation of the nitrogen–fluorine and phosphorus–fluorine diatomic systems is described. Molecular self‐consistent‐field wavefunctions near the Hartree–Fock limit were computed via the Roothaan expansion method for the $X^3{\Sigma }^{-}$ (ground), $a^1\Delta$ , and $b^1{\Sigma }^{+}$ states of NF and for the ${}^2\Pi$ states of NF⁺ and NF⁻. Similar wavefunctions were computed for the ${}^3{\Sigma }^{-}$ ground state of PF and for ${\mathrm{PF}}^{+}{(}^2\mathrm{\Pi )}$ and ${\mathrm{PF}}^{-}{(}^2\mathrm{\Pi )}$ . For the neutral molecules, the experimental bond lengths were used; for the charged species, the internuclear separations of the parent ${(}^3\mathrm{\Sigma )}$ molecules were used. In addition, a wavefunction was also obtained for ${\mathrm{PF}}^{+}{(}^2\mathrm{\Pi )}$ at its experimental internuclear separation. Values derived for the binding and ionization energies through the use of semiempirical correlation energies are in excellent agreement with experimental data; the uncorrelated excitation energies, as expected, are somewhat different than the experimental results. The electron affinities deduced from the wavefunctions indicate that the hitherto unreported NF⁻ and PF⁻ should be thermodynamically stable at moderate temperatures. Dipole and quadrupole moments have also been calculated for all the species. The second ionization potential of PF has been estimated based on Koopmans' theorem.