THE VALIDITY OF THE HARD-SPHERE MODEL IN HYDROGEN-BONDED INTERMOLECULAR INTERACTIONS OF HCN-HF

Recently obtained spectroscopic constants for excited vibrational stat es of HCN-HF with up to five quanta in the nu(7) intermolecular bendin g mode, which can be characterized as being mostly HCN hindered rotati on, and one quanta in the nu(4) intermolecular stretching mode were co mbined with earlier experimental data on this system to obtain a reduc ed intermolecular potential energy surface where the HF fragment was t reated as a pseudoatom and the HCN fragment was treated as a rigid rot or. A functional form was assumed for the interaction potential and th e vibrational dynamics was studied using a vibrational configuration i nteraction method. The parameters in the potential were varied to obta in the best fit to all available experimental data. The resulting inte raction potential was found to have a strong coupling between the nu(4 ) and nu(7) vibrational modes. The locus of constrained minima on this surface was in excellent agreement with the hard-sphere assumption us ed in the Buckingham-Fowler model [A. D. Buckingham and P. W. Fowler, J. Chem. Phys. 79, 6426 (1983)] for weakly interacting molecular dimer s. (C) 1997 American Institute of Physics. [S0021-9606(97)03244-3].