STRUCTURE OF NA(3 P-2)-AR-N CLUSTERS USING SEMIEMPIRICAL POTENTIALS

We have calculated the minimum energy geometries of clusters formed by electronically-excited sodium atoms in their (3 P-2) state with argon atoms. The potential energy functions needed to describe interactions with an open-shell atom are not pairwise additive. Those used here we re constructed using a first-order perturbation treatment. The semiemp irical pair potentials used as input were derived from direct spectros copic evidence, in the case of the A (2) Pi potential, and indirectly from matrix isolation data for the B (2) Sigma. We find the clusters t o be planar for n=2-5. Additional argon atoms form an argon subcluster , avoiding the perpendicular to the Na-Ar-5 plane. We have investigat ed the sensitivity of the cluster geometry to variations in the potent ial parameters, and predict our qualitative conclusions will not be ch anged by further data on the B potential. We propose a naming conventi on to clarify discussion of these ring-containing clusters. We have al so calculated geometric isomers for the Na-Ar-5 case. The significanc e of these findings for fluorescence experiments in cryogenic rare gas matrices and other condensed phase experiments is discussed. (C) 1998 American Institute of Physics.