A THEORETICAL-STUDY ON THE INTERNAL-ROTATION AND HYPERFINE STRUCTURES OF THE ETHYL RADICAL (CH3-CH2)

It is confirmed by the UMP2/31G** level of calculation, that the zero-point vibrational energy dominates in determining the conformational preference and the extremely low barrier to internal rotation in the ethyl radical. The isotropic hyperfine coupling constants of hydrogens and carbons of the ethyl radical have been calculated using an extended ab initio single- or multi-reference CI wavefunction (SR-CI or MR-CI). The spin density at each nucleus of interest has been calculated as a function of the basis sets and the CI-dimensions. The influence of the internal rotation of the methyl group and the inversion of the methylene group on the hyperfine coupling constants has also been studied. Furthermore, the anisotropic hyperfine coupling constants (dipolar term) have been calculated and compared with available experimental values.