Recently obtained spectroscopic constants for excited vibrational states of HCN-HF with up to five quanta in the nu(7) intermolecular bending mode, which can be characterized as being mostly HCN hindered rotation, and one quanta in the nu(4) intermolecular stretching mode were combined with earlier experimental data on this system to obtain a reduced intermolecular potential energy surface where the HF fragment was treated as a pseudoatom and the HCN fragment was treated as a rigid rotor. A functional form was assumed for the interaction potential and the vibrational dynamics was studied using a vibrational configuration interaction method. The parameters in the potential were varied to obtain the best fit to all available experimental data. The resulting interaction 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 used in the Buckingham-Fowler model [A. D. Buckingham and P. W. Fowler, J. Chem. Phys. 79, 6426 (1983)] for weakly interacting molecular dimers. (C) 1997 American Institute of Physics. [S0021-9606(97)03244-3].