THEORETICAL-STUDY OF HYPERFINE COUPLING-CONSTANTS IN ETHYL RADICAL

Spin densities that determine hyperfine splitting constants are calculated for ethyl radical from ab initio electronic wave functions. The most important direct and spin polarization contributions are obtained from single-excitation configuration interaction wave functions, in conjunction with recently developed contracted Gaussian basis sets designed specifically for spin density determination. Facile out-of-plane bending at the alpha-carbon center leads to a significant vibrational correction and temperature dependence for the alpha-carbon splitting. Coupling of torsion about the CC bond with bending at the alpha-carbon is found to have only a small effect on the hyperfine constants. For isotropic Fermi contact interactions, agreement with experiment is better than 10% for both carbons and for the alpha-hydrogens. The larger 28% error found for the beta-hydrogens is attributed primarily to the missing effects of electron correlation. Anisotropic dipolar hyperfine constants are also evaluated and agree well with experiment wherever comparison is possible.