Transition from a Bloch-Wilson to a free-electron density of states in Zn(n)- clusters

We present photoelectron spectroscopy studies on Zn(n) (-) in the size range of n=3-117. We show that zinc clusters exhibit a distinct transition in their electronic structure as a function of size. At small sizes (up to n=18) the clusters follow the Bloch-Wilson picture of the development of a metal from closed-shell atoms, exhibiting a gradual decrease of the gap between the fully occupied s band and the empty p band. For large sizes (n approximately or > 32) the band overlap allows the valence electrons to fully delocalize. This leads to an almost perfect free-electron density of states, as is demonstrated by discussing the spectra in the light of standard free-electron models and by comparison to the results obtained on sodium clusters.     

Symmetry and electronic structure of noble-metal nanoparticles and the role of relativity

We present high resolution UV-photoelectron spectra of cold mass selected Cun-, Agn-, and Aun- with n=53-58. The observed electron density of states is not the expected simple electron shell structure, but is strongly influenced by electron-lattice interactions. Only Cu55- and Ag55- exhibit highly degenerate states. This is a direct consequence of their icosahedral symmetry, as is confirmed by density functional theory calculations. Neighboring sizes exhibit perturbed electronic structures, as they are formed by removal or addition of atoms to the icosahedron and therefore have lower symmetries. Gold clusters in the same size range show completely different spectra with almost no degeneracy, which indicates that they have structures of much lower symmetry. This behavior is related to strong relativistic bonding effects in gold, as demonstrated by ab initio calculations for Au55-.     

Communication: Highest occupied molecular orbital-lowest unoccupied molecular orbital gaps of doped silicon clusters from core level spectroscopy

A method to determine band gaps of size-selected and isolated nanoparticles by combination of valence band and core-level photoionization spectroscopy is presented. This approach is widely applicable and provides a convenient alternative to current standard techniques for the determination of band gaps by optical or photoelectron spectroscopy. A first application to vanadium doped silicon clusters confirms a striking size-dependence of their highest occupied-lowest unoccupied molecular orbital gaps.     

Ground state and response properties of mercury clusters

The change of the cohesive energy and the optical absorption spectra of small singly sized Hg clusters is discussed. The cohesive energy allows one to determine the different regimes of chemical bonding. The optical spectra show an abrupt transition to a collective, plasmon-like absorption as a function of increasing cluster size. The position of the one plasmon peak is: 1) independent of the charge state, 2) nearly independent of cluster size, and 3) agrees with that of the classical Mie plasmon calculated from the experimental dielectric constants. The width of the plasmon peaks is discussed. A strong influence of electronic correlations on the cluster size dependence of the oscillator strength is observed.     

Access to the Bis‐benzene Cobalt(I) Sandwich Cation and its Derivatives: Synthons for a “Naked” Cobalt(I) Source?

The synthesis and structural characterization of the hitherto unknown parent Co(bz)₂⁺ (bz=benzene) complex and several of its derivatives are described. Their synthesis starts either from a CoCO₅⁺ salt, or directly from Co₂(CO)₈ and a Ag⁺ salt. Stability and solubility of these complexes was achieved by using the weakly coordinating anions (WCAs) [Al(OR^F)₄]^? and [F{Al(OR^F)₃}₂]^? {R^F=C(CF₃)₃} and the solvent ortho‐difluorobenzene (o‐DFB). The magnetic properties of Co(bz)₂⁺ were measured and compared in the condensed and gas phases. The weakly bound Co(o‐dfb)₂⁺ salts are of particular interest for the preparation of further Co^I salts, for example, the structurally characterized low‐coordinate 12 valence electron Co(P^tBu₃)₂⁺ and Co(NHC)₂⁺ salts.     

Exposing the Oxygen-Centered Radical Character of the Tetraoxido Ruthenium(VIII) Cation [RuO4]+

The tetraoxido ruthenium(VIII) radical cation, [RuO₄]⁺, should be a strong oxidizing agent, but has been difficult to produce and investigate so far. In our X-ray absorption spectroscopy study, in combination with quantum-chemical calculations, we show that [RuO₄]⁺, produced via oxidation of ruthenium cations by ozone in the gas phase, forms the oxygen-centered radical ground state. The oxygen-centered radical character of [RuO₄]⁺ is identified by the chemical shift at the ruthenium M₃ edge, indicative of ruthenium(VIII), and by the presence of a characteristic low-energy transition at the oxygen K edge, involving an oxygen-centered singly-occupied molecular orbital, which is suppressed when the oxygen-centered radical is quenched by hydrogenation of [RuO₄]⁺ to the closed-shell [RuO₄H]⁺ ion. Hydrogen-atom abstraction from methane is calculated to be only slightly less exothermic for [RuO₄]⁺ than for [OsO₄]⁺.