The inversion barriers of NF3, NCl3, PF3, and PCl3. A theoretical study

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Abstract
The inversion barriers of NF3, NCl3, PF3, and PCl3 have been calculated from ab initio molecular orbital theory using large basis sets including polarization functions on the central atom. The calculated inversion barriers (in kcal/mole) are 78.5(NF3), 22.9(NCl3), 121.5(PF3), and 90.8(PCl3). The NF3 inversion barrier is clearly larger than the experimental first bond dissociation energy (∼57 kcal/mole), indicating that planar NF3 is not bound relative to NF2+F. For PF3 and PCl3, bond dissociation is energetically competitive with inversion, since the experimental first bond dissociation energies are 130±14 and 81±5 kcal/mole, respectively. The lowest energy closed shell electronic configuration for planar PF3 is shown to have the phosphorus nonbonding (lone pair) electrons in a A1′ type orbital, rather than the pure p orbital of A2″ symmetry usually assumed for molecules of this type. Limiting the description of inner shells to a minimum basis set is shown to have relatively small (0–3 kcal/mole) effects on the calculated barrier.

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