Anisotropy of the nuclear spin coupling in PH−2, PH3, and PH+4 molecules

Abstract

The anisotropy of the nuclear spin–spin coupling tensor, relative to P, H and H, H interacting nuclei, has been investigated by means of extended ab initio calculations in the molecules PH−2, PH3, and PH+4. The coupled Hartree–Fock perturbed scheme has been employed retaining the nonrelativistic Ramsey Hamiltonians. The most important contributions to the anisotropy in the P, H coupling arise from the Fermi contact-spin-dipolar cross term, which is partially counterbalanced by the spin-orbit effect. The discrepancies emerging between computed and experimental J(P,H) in phosphine and phosphonium are interpreted in terms of neglected electron correlation contributions. A dramatic sensitivity of the Fermi contact term of the molecular geometry has been found for PH2−. The calculations show that the P–H coupling is more anisotropic than N–H, which is seemingly due to the enhanced nonsphericity of electron distribution.