Characterization of ArnCl(-) clusters (n=2-15) using zero electron kineticenergy and partially discriminated threshold photodetachment spectroscopy

ArnCl- clusters have been investigated by anion zero electron kinetic energ y (ZEKE) and partially discriminated threshold photodetachment spectroscopy . The experiments yield size-dependent electron affinities (EAs) and electr onic state splittings for the X, I, and II states accessed by photodetachme nt. Cluster minimum energy structures have been determined from calculation s based on a "simulated annealing" approach employing our recently presente d Ar-Cl(-) pair potentials from anion ZEKE spectroscopy [T. Lenzer, I. Your shaw, M. R. Furlanetto, G. Reiser, and D. M. Neumark, J. Chem. Phys. 110, 9 578 (1999)] and various nonadditive terms. The EAs calculated without many- body effects overestimate the experimental EAs by up to 1500 cm(-1). Repuls ive many-body induction in the anion clusters is found to be the dominant n onadditive effect. In addition, the attractive interaction between the chlo ride charge and the Ar-2 exchange quadrupole is important. These findings a re consistent with our earlier results for XenI-, ArnI-, and ArnBr- cluster s and highlight again the necessity of an adequate implementation of many-b ody effects to describe the energetics of such systems. For ArnCl- clusters with n > 12 we find some deviations between experimental and calculated (0 K) EA which can be explained by the population of less stable anion struct ures due to the finite temperatures of the clusters in our experiments. Thi s results in lower EAs than predicted for the corresponding global minimum energy structures. (C) 2001 American Institute of Physics.