ANION PHOTOELECTRON-SPECTROSCOPY OF I-2(-) AND I-2(-)CENTER-DOT-AR-N (N = 1-14, 16, 20) CLUSTERS

We report the mass-selected anion photoelectron spectra of I-2(-) and the weakly bound clusters I-2(-). Ar-n (n = 1 - 14, 16, 20) measured a t a photon energy of 4.657 eV. The experiment yields size-dependent ve rtical and adiabatic detachment energies for the formation of the grou nd state and five valence-excited states of the neutral cluster, which correspond to the (1)Sigma(g)(+) (X), (II2u)-I-3 (A'), (II1u)-I-3 (A) , (II0)-I-3-(u) (B'), (II1u)-I-1 (B ''), and (II0)-I-3+(u) , (B) state s of bare I-2 The detachment energies are successively blue-shifted wi th increasing cluster size, indicating a stronger stabilization of the anionic cluster relative to the neutral counterpart. The blue shift i s of similar extent for the electronically excited states A' and A and approximately 10% less for the X state. The I-2(-) and I-2(-). Ar spe ctra are simulated employing a Franck-Condon analysis, from which we e stimate the ion vibrational temperature and determine the I-2(-)-Ar bi nding energy (D-0= 53+/-4 meV). The results are discussed with respect to possible cluster geometries and the evolution of the total and ste pwise solvation energies. For I-2(-). Ar-6 We present evidence that al l Ar atoms are bound around the waist of the I-I bond. (C) 1998 Americ an Institute of Physics.