Molecular orbital studies of hyperfine coupling constants in the H2CN and H(HO)CN radicals

Abstract

Isotropic magnetic hyperfine splittings have been evaluated for the closely related H{sub 2}CN and H(HO)CN radicals from ab initio molecular orbital models. Uncertainties in the equilibrium geometries appear to have little effect on the carbon and nitrogen splittings but may affect the large methylene hydrogen splittings by up to several gauss. Vibrational averaging is estimated to provide corrections on the order of only 1 G or less at all nuclei. Direct, spin-polarization, and electron correlation effects all contribute about equally to the large methylene hydrogen splitting in each radical, as well as to the large difference in this splitting between the two radicals. The electron correlation contribution is the most difficult to calculate, and neither of the two distinct procedures utilized to study that effect provides a fully quantitative description at the limit of currently feasible calculations.