Barrier to Internal Rotation in Ethane

A series of SCF LCAO MO computations for the ethane molecule are reported for both the staggered and eclipsed form. The obtained wavefunctions are better than those previously reported in literature. From this work the following conclusions can be derived. (1) The height of the internal rotation barrier is rather insensitive to the choice of the basis set. This explains the good agreement between computed and experimental barrier height found by Pitzer and Lipscomb. These authors obtained a total energy of −78.99115 a.u. for the staggered form and −78.98593 a.u. for the eclipsed form. Our best computation gives a total energy of −79.10824 a.u. for the staggered form and −79.10247 a.u. for the eclipsed form. The experimental barrier height is 0.0048±0.0005 a.u. (3.03±0.3 kcal). (2) The SCF LCAO MO functions are adequate in reproducing the barrier; therefore correlation effects are rather unimportant. As a consequence, these computations support indirectly the simple electrostatic model advanced, for example, by Karplus and Parr.