Au10-: isomerism and structure-dependent O2 reactivity.

Structure isomers of the Au(10)(-) cluster and their chemical reactivity with O(2) are studied using photoelectron spectroscopy under different experimental conditions. In addition to the global minimum triangular D(3h) structure, at least three low-lying isomers (X', X'', and X''') are observed distinctly using argon tagging and O(2) titration. The D(3h) structure has a very high electron affinity of 3.88 eV, whereas the low-lying isomers have lower electron affinities (2.86, 3.09, and 3.45 eV for X', X'', and X''', respectively). It is found that the D(3h) global minimum does not react with O(2) and can only form a physisorbed Au(10)(O(2))(-) van der Waals complex under cold experimental conditions. The three low-lying isomers are reactive with O(2) and can be systematically titrated out of the cluster beam using an O(2)-seeded carrier gas, leaving a clean D(3h) Au(10)(-) beam.