Lawrence Berkeley National Laboratory

Reaction of gold atoms with acetylene and ethylene in a laser ablation source produces a number of gold-containing species. Their photoionization efficiency (PIE) curves are measured using tunable vacuum ultraviolet (VUV) radiation at the Advanced Light Source. Their structures are assigned by comparing the experimental ionization energies and PIE curves to those of potential isomers calculated at the CAM-B3LYP/aug-cc-pVTZ level. For smaller molecules, the contribution of ionization to excited electronic states of the cation is also included using photoionization cross sections calculated using ePolyScat. Reaction with acetylene produces adducts Au(C₂H₂) and Au(C₂H₂)₂, as well as HAu(C₄H₂). Reaction with ethylene leads to adducts Au(C₂H₄), Au(C₂H₄)₂, an adduct with a gold dimer, Au₂(C₂H₄), as well as the gold hydrides AuH, HAu(C₂H₄), and HAu(C₄H₄). [Au,C4,H7] is also observed, and it likely corresponds to a gold alkyl, H₂C═C(H)-Au(C₂H₄). Reactions leading to production of odd-hydrogen species are endothermic and are likely due to translationally or electronically excited gold atoms. These measurements provide the first directly measured ionization energy for gold hydride, IE(AuH) = 10.25 ± 0.05 eV. Combining this value with the dissociation energy of AuH⁺ gives a dissociation energy D₀(AuH) = 3.15 ± 0.12 eV. Several other ionization energies are measured: IE(Au₂(C₂H₄)) = 8.42 ± 0.05 eV, IE(HAu(C₂H₄)) = 9.35 ± 0.05 eV, IE(HAu(C₄H₂)) = 8.8 ± 0.1 eV, and IE(HAu(C₄H₄)) = 8.8 ± 0.1 eV.