Calculation of the Dissociation Energy of NH by a Semiempirical Interpolative Method

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Abstract
Simple valence bond wave functions (using hybridized orbitals) are constructed for the CH, NH, and OH molecules. The intraatomic energy is evaluated by Moffitt's atoms‐in‐molecules method. The interatomic energy is approximated by: (1) replacing heavy‐atom 1s electrons by point charges at their nuclei; (2) restricting exchange energy contribution to permutation of bonding electrons; (3) using Mulliken approximation to reduce exchange and hybrid integrals to Coulomb and overlap types; (4) evaluating one‐center integrals by the Pariser approximation and by a new method which utilizes the virial theorem; and (5) expressing two‐center integrals by simplified expressions which give correct semiempirical values at R=0 limit and which contain two arbitrary parameters. The latter are adjusted so as to yield correct dissociation energies of CH and OH. The dissociation energy of NH is then found to be 3.61 ev, which lies within the uncertainty of the best experimental result 3.7±0.5 ev. Calculated degrees of hybridization agree well with previous estimates.

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