Equilibrium structure and hyprfine parameters of the ethane cation

Abstract A C 2h , structure of the ethane cation, with a “normal” CC bond length, was found as the lowest minimum in the MP2/6-31G** potential energy surface, in contrast to previous, less accurate, ab initio calculations, which have produced a “long-bond” structure with D 3d symmetry for the ground state. A largest isotropic hyperfine coupling constant (hcc) of 131 G is obtained from accurate configuration interaction calculations at the MP2/6-31G** optimized C 2h geometry, in good agreement with the experimental value of 152.5 G. MP2/6-311 + +G** and MP2/6-311G(2d, 2p) calculations confirm the existence of this C 2h , structure, predicting a geometry almost identical with the one obtained in the MP2/6-31G** optimization calculations, and hcc values of 130–133 G. For the out-of-plane protons, hcc values of −8.5 to 8.8 G are obtained, in excellent agreement with the experimental value of −9.0 G.