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 V, whereas the low-lying, isomers have lower electron affinities (2.86, 3.09, and 3.45 eV for X', X '', X''', respectively). It is found that the D-3h global minimum does not react with O2 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.