Laser ablation and gas-phase reactions of small gold cluster ions, Aun+ (1⩽n⩽7)

Abstract

The abundance distributions of gold cations, Aun+ for 1⩽n⩽7, generated by pulsed laser ablation of gold metal were determined by time-of-flight mass spectrometry. The odd-n ions, Au3+, Au6+, and Au7+ were particularly abundant, consistent with previous results understood by rudimentary molecular orbital bonding models. A unique aspect of our experiment was the ability to enhance concentrations of the larger Aun+ by sampling slower ions in the tail of the ablation plume; this effect indicates ion formation under quasiequilibrium (high temperature) conditions. The primary goal of this study was to examine gas-phase reactions of Aun+ for n=1–7 by injecting a hydrocarbon or halocarbon into the ion trajectory and determining compositions/abundances of the resulting complex ions, Aun+-L, formed by abstraction of a ligand(s) L from the organic molecule(s). Among the more significant products were the carbides AunCc+, for n⩽7 and c⩽4. The Aun+-L products and distinctive n-dependent variations in product compositions and abundances are interpreted in the context of organogold bonding and condensed phase gold cluster chemistry. The coherence of the exhibited chemistries demonstrates the value of this approach in examining novel transition metal cluster ion chemistry despite the potential for internal excitation of nascent laser-ablated cluster ions. This approach offers a means to prepare new heteronuclear clusters, including noble metal carbides, which may exhibit unique properties.