Anion photoelectron spectroscopy of I2- and I2-•Arn (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 at a photon energy of 4.657 eV. The experiment yields size-dependent vertical and adiabatic detachment energies for the formation of the ground 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) states of bare I-2 The detachment energies are successively blue-shifted with increasing cluster size, indicating a stronger stabilization of the anionic cluster relative to the neutral counterpart. The blue shift is 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 spectra are simulated employing a Franck-Condon analysis, from which we estimate the ion vibrational temperature and determine the I-2(-)-Ar binding energy (D-0= 53+/-4 meV). The results are discussed with respect to possible cluster geometries and the evolution of the total and stepwise solvation energies. For I-2(-). Ar-6 We present evidence that all Ar atoms are bound around the waist of the I-I bond. (C) 1998 American Institute of Physics.