Correlation Effect in the Rotation Barrier of Ethane

An ab initio calculation of the barrier to internal rotation in ethane using a minimum basis of Slater-type atomic orbitals is reported. Electron correlation is partly taken into account by a second-order perturbation method. It decreases the barrier by 0.13 kcal/mol with respect to the SCF value of Pitzer or 0.17 kcal/mol with respect to another set of bond orbitals. These small lowerings are discussed in terms of localized orbitals.