Bernd von Issendorff

Gas-phase production and photoelectron spectroscopy of the smallest fullerene,C20

Fullerenes are graphitic cage structures incorporating exactly twelve pentagons. The smallest possible fullerene is thus C20, which consists solely of pentagons. But the extreme curvature and reactivity of this structure have led to doubts about its existence and stability. Although theoretical calculations have identified, besides this cage, a bowl and a monocyclic ring isomer as low-energy members of the C20 cluster family, only ring isomers of C20 have been observed so far. Here we show that the cage-structured fullerene C20 can be produced from its perhydrogenated form (dodecahedrane C20H 20) by replacing the hydrogen atoms with relatively weakly bound bromine atoms, followed by gas-phase debromination. For comparison we have also produced the bowl isomer of C20 using the same procedure. We characterize the generated C20 clusters using mass-selective anion photoelectron spectroscopy; the observed electron affinities and vibrational structures of these two C20 isomers differ significantly from each other, as well as from those of the known monocyclic isomer. We expect that these unique C20 species will serve as a benchmark test for further theoretical studies.

Irregular variations in the melting point of size-selected atomic clusters

Small particles have a lower melting point than bulk material. The physical cause lies in the fact that small particles have a higher proportion of surface atoms than larger particles—surface atoms have fewer nearest neighbours and are thus more weakly bound and less constrained in their thermal motion, than atoms in the body of a material. The reduction in the melting point has been studied extensively for small particles or clusters on supporting surfaces. One typically observes a linear reduction of the melting point as a function of the inverse cluster radius,,. Recently, the melting point of a very small cluster, containing exactly 139 atoms, has been measured in a vacuum using a technique in which the cluster acts as its own nanometre-scale calorimeter,. Here we use the same technique to study ionized sodium clusters containing 70 to 200 atoms. The melting points of these clusters are on average 33% (120 K) lower than the bulk material; furthermore, we observe surprisingly large variations in the melting point (of ±30 K) with changing cluster size, rather than any gradual trend. These variations cannot yet be fully explained theoretically.

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-.

Low temperature photoelectron spectra of water cluster anions

Photoelectron spectra of cold (10 K) size selected water cluster anions (H(2)O)(n) (-) and (D(2)O)(n) (-) have been measured in the size range n=20-120. A new isomer with a higher binding energy than the so-called isomer I has been identified, which appears in the size range n=25-30 and for (H(2)O)(n) (-) becomes dominant at n=46. Magic numbers observed in the mass spectra of the cluster anions provide evidence that this new isomer class consists of clusters with an internal electron.

Spin and orbital magnetic moments of size-selected iron, cobalt, and nickel clusters

Spin and orbital magnetic moments of cationic iron, cobalt, and nickel clusters have been determined from x-ray magnetic circular dichroism spectroscopy. In the size regime of

Coordination-driven magnetic-to-nonmagnetic transition in manganese-doped silicon clusters

n = 10 - 15

Ground state and response properties of mercury clusters

atoms, these clusters show strong ferromagnetism with maximized spin magnetic moments of 1~

Penetration of thin C60 films by metal nanoparticles.

\mu_B

Magnetic moments of chromium-doped gold clusters: The anderson impurity model in finite systems

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Insulating or Metallic: Coexistence of Different Electronic Phases in Zinc Clusters

3d