Coriolis coupling and the anomalous rotational isotope effect for CN-H-2/D-2(j(2)=1) van der Waals complexes

Rotational constants for CN(X)-H-2/D-2(j(2) = 1), derived from electronic s pectra, exhibit an unusually small dependence on H-2/D-2 isotopic substitut ion. In the present study, variational bound state calculations were carrie d out to examine the origin of this effect. A four-dimensional potential en ergy surface [J. Chem. Phys. 110 (1999) 10380] was used for this model. The results show that the lowest energy rotational manifolds of CN(X)-H-2/D-2( j(2) = 1) are significantly influenced by Coriolis state mixing. This pertu rbation is most pronounced for CN-H,, and is identified as the cause of the anomalous isotope effect. (C) 2001 Elsevier Science B.V. All rights reserv ed.