The hyperfine structure in the ethylene radical cation : an accurate CI study

Abstract The hyperfine structure in the ethylene radical cation, including isotropic and anisotropic coupling constants for H and 13 C, has been computed from accurate CI wavefunctions calculated at the experimental geometry. The isotropic hyperfine coupling constant for the protons is obtained as −4.5 G and for the carbon atoms −3.0 G for a torsion angle 25°. The calculated a H value was found to be very sensitive to the torsion angle around the CC bond. This fact was used to obtain an independent estimate of 28° for the torsion angle from recent ESR measurements.