Probing Reactivity of Gold Atoms with Acetylene and Ethylene with VUV Photoionization Mass Spectrometry and Ab Initio Studies.

Abstract

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.