Coriolis coupling and the anomalous rotational isotope effect for CN–H2/D2(j2=1) van der Waals complexes

Rotational constants for CN(X)–H2/D2(j2=1), derived from electronic spectra, exhibit an unusually small dependence on H2/D2 isotopic substitution. In the present study, variational bound state calculations were carried out to examine the origin of this effect. A four-dimensional potential energy surface [J. Chem. Phys. 110 (1999) 10380] was used for this model. The results show that the lowest energy rotational manifolds of CN(X)–H2/D2(j2=1) are significantly influenced by Coriolis state mixing. This perturbation is most pronounced for CN–H2, and is identified as the cause of the anomalous isotope effect.