Effect of vibrations on the internal rotation barrier in ethane

Abstract
The effect on the ethane internal rotation barrier of (1) zero‐point vibrational averaging and (2) distortions in equilibrium geometry during internal rotation is determined. We find that the (previously ignored) averaging term is 374±90 cal/mole which is substantially larger, and opposite in sign, to the distortion correction of −161±20 cal/mole. The isotope shift, other experimental tests, and some important implications of our results are discussed.