Hindered internal rotation in molecular systems: quantum statistics of equilibrium and rate constants in the Wigner function formalism

Summary The quantum statistics of a symmetric hindered internal rotator in a molecule or molecular complex is developed within the Wigner function formalism. Different shapes of the rotational barrier are considered. The partition function and the thermodynamic functions are given as Wigner-Kirkwood series expansions in terms of powers of Planck's constant squared. One gets simple closed expressions containing the modified Bessel functionsJ₀ andJ₁ of the argumentiV₀/2kT whereV₀ is the barrier height. Some problems concerning the evaluation of equilibrium and rate constants of chemical reactions are discussed.Supported by the Alexander von Humboldt-Stiftung