Internal Rotation in Completely Asymmetric Molecules. IV. Energy Contributions from the α Dependence of the Torsional Kinetic Energy

For molecules with asymmetric internal rotors, the reduced moment of inertia for the torsional motion depends explicitly upon α, the angle of internal rotation. General expressions have been obtained for this dependence from a model which considers one degree of internal freedom for molecules with one part planar and the other with a plane of symmetry. The formulas are functions only of the inertial parameters of the molecule. For those cases where the α dependence is small, the results are expanded in trigonometric series. In this case the α dependence of the torsional kinetic energy may be expressed as a variation in the effective potential hindering the internal motion. Torsional coefficients have been calculated for some representative molecules.