Calculation of the Barrier to Internal Rotation in Ethane with Improved Exponential Wavefunctions

A minimum set of Slater exponential orbitals is used to construct molecular orbital wavefunctions for staggered and eclipsed ethane. The orbital exponents chosen are those which are optimum for methane, rather than those obtained from Slater's rules, as were used previously. The value of the internal rotation barrier is calculated to be 3.5 kcal/mole. Comparison with other calculations indicates that the barrier is fairly insensitive to choice of basis functions and to the value of the total energy.