Hindered rotation of adsorbed diatomic molecules

Ortho-para separation factors for H2 and D2 are discussed in terms of two models of hindered rotation in the adsorbed phase. Although the available experimental data do not provide a definitive test of the models, it appears that both rotational modes are perturbed, and that a model incorporating hindrance of both modes is capable of fitting both the observed magnitude and temperature dependence of the separation factors.