The two-dimensional electron system Au/Ge(111)-(√ 3 × √ 3)R30 • is studied in detail by angle-resolved photoemission and density functional theory calculations. In combining these results, we identify four metallic bands which are either of dominantly Au or Ge character, respectively. The largest Fermi surface sheet, originating from Au orbitals, is suggestive of a nesting condition due to its hexagonal shape. However, a charge density wave transition is not observed between room temperature and 10 K. The electronic structure obtained by density functional theory with inclusion of a self-energy correction is in good agreement with the experiment. These calculations also indicate that there is significant spin-orbit splitting, especially in the Au-related bands, which is partly of Rashba character.

Understanding the bonding of gold(I) species has been central to the development of gold(I) catalysis. Herein, we present the synthesis and characterization of the first gold(I)‐cyclobutadiene complex, accompanied with bonding analysis by state‐of‐the‐art energy decomposition analysis methods. Analysis of possible coordination modes for the new species not only confirms established characteristics of gold(I) bonding, but also suggests that Pauli repulsion is a key yet hitherto overlooked element. Additionally, we obtain a new perspective on gold(I)‐bonding by comparison of the gold(I)‐cyclobutadiene to congeners stabilized by p‐, d‐, and f‐block metals. Consequently, we refine the gold(I) bonding model, with a delicate interplay of Pauli repulsion and charge transfer as the key driving force for various coordination motifs. Pauli repulsion is similarly determined as a significant interaction in AuI‐alkyne species, corroborating this revised understanding of AuI bonding.

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Spectroscopic measurements in the vacuum ultraviolet (VUV) regime are difficult to make due to extremely large absorption of VUV radiation in most materials. This paper describes an experimental setup designed for studying the optical emission during pulsed surface flashover for the wavelength range between 115 nm to 300 nm at atmospheric pressures. A vacuum monochromator VM 505 from Acton Research Corporation was used as the spectrograph. For VUV transmission down to 115 nm the light emitted by surface flashover across an MgF 2 window (front side of window in air, backside in vacuum) was focused by an MgF 2 lens onto the entrance slit of the spectrograph. A quartz window with sodium salicylate coating exposed to the spectrograph's vacuum was placed in the exit focal plane of the collimating mirror of the spectrograph. This fluorescent coating downconverts the VUV light to longer wavelengths that were recorded with an Andor DH520 series ICCD camera in combination with a Nikon 105 mm lens. Spectra were measured at atmospheric pressure with a flashover spark length of about 9 mm and DC excitation with a capacitance of 4.1 nF. Emission spectra were measured from 300 nm down to 130 nm. In parallel, theoretical spectra were calculated primarily for the identification of radiating species and their temperature. Utilizing the NIST Atomic Spectra Database (ASD) data a library of temperature dependent optical emission spectra was generated with SpectraPlot, a spectral software suite developed at TTU. VUV spectral lines of nitrogen, carbon, magnesium and silicon were identified. In pure nitrogen, for instance, the nitrogen I double line at 174.3 nm and 174.5 nm is clearly visible in the spectrum along with a strong double line at 279.6 nm and 280.4 nm, which is emitted by Magnesium II, eroded from the surface exposed to flashover. Spectra were measured in ambient air, pure nitrogen, and argon. An experiment upgrade is currently underway, increasing the VUV sensitivity of the setup. The measured spectra will be discussed in relation to the physics of surface flashover and volume breakdown at atmospheric pressure. _____________________________ * Work supported by the Air Force Office of Scientific Research 978-1-4244-2636-2/09/$25.00 ©2009 IEEE