Theoretical explanation of strong enhancement of alkali metal ion neutralization on au nanoclusters

We present a theoretical study of alkali metal ion neutralization on gold nanoclusters. The experimental time-of-flight measurements show that neutral fraction of alkali metal ions scattered from flat Au surface is low (3%-15%), but it increases up to 50% for small Au clusters. Several possible explanations of alkali metal ions neutralization enhancement on nanoclusters have been proposed earlier, but they do not fully explain existing experimental data. We introduce alternative explanation of neutralization probability enhancement for small clusters. It is based on ion energy level shift due to interaction with image/induced charges, which significantly differs in the case of metallic nanocluster and in the case of flat continuous metallic surface. Another known mechanism is greater neutralization rate on positively charged edge atoms of Au nanocluster. The combination of two mechanisms and difference in atomic radii possibly explains greater neutralization probability enhancement for Na⁺ in comparison to Li⁺.