VIBRATIONAL DYNAMICS OF (HF)N AGGREGATES FROM AN ABINITIO BASED ANALYTICAL (1+2+3)-BODY POTENTIAL

We have fitted an analytical 12-dimensional three-body potential type hypersurface for the hydrogen fluoride system with a weighted root mean square deviation of 62.8cm-1 at 1004 geometries for (HF)3, selected by a quantum sampling technique, calculating electronic potential energies by correlated ab-initio techniques at the DZP+MP2 level. Extensive test calculations with larger basis sets and for larger (HF)n aggregates show that the analytical three-body term gives an excellent description of the (HF)3 potential hypersurface and a good approximation for clusters up to at least the pentamer, when used in combination with the experimental high quality pair potential previously obtained by us. We have calculated for the first tune a reliable, fully anharmonic binding energy with respect to 3 HF to be D0[(HF)3]=43.34kJmol-1 by means of vibrational quautum Monte Carlo calculations using this potential (nuclear dynamical error < 0.1kJmol-1, electronic error estimate < 1kJmol-1). This is compared to D0 for other (HF)n aggregates (n = 2 to 7). We systematically explore energetic effects from D isotope substitution on the dissociation energies and vibrational predissociation channels. Anharmonic predictions for the infrared spectrum of (HF)3 are made.