Probing the electronic structure and Au-C bonding in AuC₂H (n = 4-7) using photoelectron imaging spectroscopy and...

We report a combined experimental and theoretical study on the structures and chemical bonding of AuC₂H (n = 4-7) using photoelectron imaging and quantum chemical calculations. All the ground states of anions and neutral AuC₂H have a linear geometry. The electron affinities (EAs) are measured to be 2.063(5), 2.157(5), 2.220(5), and 2.267(5) eV for AuC₂H, n = 4-7, respectively. The photoelectron imaging data of AuC₈H^- and AuC₁₀H^- reveal major vibrational progressions in the Au-C stretching modes. The ground state stretching frequencies of the titled neutral molecules are 226, 193, 177, and 128 cm^-1, respectively. By comparing the experimental β value and theoretical molecular orbital analysis, we confirm that the CAM-B3LYP method is more suitable for describing the properties of such unsaturated long chains organogold clusters. The experimental and CAM-B3LYP methods give a big picture of the trend in EAs of AuC₂H. This shows that the EA value becomes larger with an increase in the carbon chain length, and it also shows a slow increment for larger n. The NRT analysis shows that the change of the Au-C bond order is not obvious as the number of carbon atoms increases, and the covalent character dominates the Au-C chemical bonds in these neutral species. The current study provides a wealth of electronic structure information about long-chain AuC₂H^- (n = 4-7) and their corresponding neutral counterparts.