On the Determination of Barriers to Internal Rotation

A method is presented for determining barriers to internal rotation directly from the spectrum of torsional energy levels without an a priori knowledge of either molecular geometry or the dynamics of the motion. The method is applied to the H₂O₂ and D₂O₂ molecules. It is also shown that the neglect of the variation of the effective inverse moment of inertia of threefold rotors can lead to an apparent $V_6$ contribution to the potential function.