Least-squares mass-dependence molecular structures for selected weakly bound intermolecular clusters

The applicability of the recently proposed method of Watson et al. [J. Mol. Spectrosc. 196 (1999) 102] to the determination of geometries of weakly bound clusters was tested. The method delivers equilibrium-quality structural parameters from highly precise fits to only the ground state rotational constants and very encouraging results were obtained for several families of clusters: Rg-HX, N-2-HX, H2O-HX, and Ar2HX. Considerable improvement in standard deviations of least-squares fits of geometry relative to ground state fits was obtained. In cases where corroborating information concerning the values of equilibrium geometrical parameters was available, those were found to be reproduced successfully, in particular for Ar-HF, Ar-HCl, H2O-HF, and H2O-HCl The long established large amplitude structural averaging correction for complexed hydrogen halides, based on a quadrupolar averaging angle, was found to be a well-defined term in the parameterisation of vibration-rotation contributions to the ground state moments of inertia. However, it is one of several mutually canceling terms and is not necessarily a dominating term in the vibration-rotation contribution. A computer code for such calculations is made available. (C) 2003 Elsevier Science (USA). All rights reserved.