High-resolution ion mobility measurements of indium clusters: electron spill-out in metal cluster anions and cations

High-resolution ion mobility measurements have been used to examine In-n(-) and In-n(+) clusters with n = 2-30. The cluster-He scattering cross-sectio ns of the anions are systematically larger than those of the cations. The d ifference (similar to 25% for In-2 to similar to 2% for In-30) is attribute d to the electron density extending further from the surface of the cluster in the anions than in the cations. Geometric cross-sections estimated from electron densities determined from a charged jellium model are in good agr eement with the experimental data: the change in cross-section with charge state is reproduced over the entire range. (C) 1999 Elsevier Science B.V. A ll rights reserved.