The neutralization of 3 keV K-39(+) ions scattered from Au nanoclusters deposited on TiO2(110) was measured with time-of-flight spectroscopy. All of the K remains ionic in scattering from a Au thin film or from large clusters, but up to similar to 20% is neutralized in scattering from small clusters. The results demonstrate that the K 4s ionization level couples to states associated with Au nanoclusters, such that the neutralization probability is a function of the nanocluster size. The data are compared to previous experiments with Na and Li projectiles. (c) 2007 American Vacuum Society.