CALCULATIONS OF THE SPECTRA OF RARE-GAS DIMERS AND TRIMERS - IMPLICATIONS FOR ADDITIVE AND NONADDITIVE INTERMOLECULAR FORCES IN NE-2-AR, NE-2-KR, NE-2-XE, AR-2-NE, AR-3, AR-2-KR AND AR-2-XE

Calculations of ground-state energies and rotational constants are car ried out for a variety of van der Waals dimers and trimers formed from Ne, Ar, Kr and Xe. It is found that the existing pair potentials for Ne-Ar, Ne-Kr and Ne-Xe do not adequately reproduce the measured rotati onal constants of the van der Waals dimers. Modified pair potentials, with equilibrium distances that differ from the originals by less than 1% but give much better rotational constants, are then proposed. Calc ulations of rotational constants for Ne-2-Ar, Ne-2-Kr and Ne-2-Xe are carried out using pairwise-additive potentials constructed from both t he original and the modified pair potentials. The modified pair potent ials give much better agreement with experiment for the trimers as wel l as the dimers. The effect of an Axilrod-Teller triple-dipole term on the rotational constants is considered, and found to be significant, especially for the A rotational constant. However, the best available Ne-Ne potential is not accurate enough to allow unambiguous informatio n on three-body forces to be extracted. (C) 1995 American Institute of Physics.