The heat capacity of a free cluster has been determined from the temperature dependence its photofragmentation mass spectrum. data for spherical sodium ${\mathrm{Na}}_{N}^{+}$, with $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}139$, show maximum at 267 K, which is interpreted as solid-to-liquid phase transition in this finite system. melting point lies 104 or 28% lower than that bulk sodium. latent fusion reduced by 46%.

The activation of CO2 and its hydrogenation to methanol are much interest as a way utilize captured CO2. Here, we investigate the use size-selected Cu4 clusters supported on Al2O3 thin films for reduction in presence hydrogen. catalytic activity was measured under near-atmospheric reaction conditions with low partial pressure, oxidation state investigated by situ grazing incidence X-ray absorption spectroscopy. results indicate that most active low-pressure catalyst conversion CH3OH. Density...

There exists a surprising theoretical prediction for small system: its microcanonical heat capacity can become negative. An increase of energy can-under certain conditions-lead to lower temperature. Here we present experimental evidence that cluster containing exactly 147 sodium atoms does indeed have negative near solid liquid transition.

We present high resolution UV-photoelectron spectra of cold mass selected ${\mathrm{C}\mathrm{u}}_{n}^{\ensuremath{-}}$, ${\mathrm{A}\mathrm{g}}_{n}^{\ensuremath{-}}$, and ${\mathrm{A}\mathrm{u}}_{n}^{\ensuremath{-}}$ with $n=53--58$. The observed electron density states is not the expected simple shell structure, but strongly influenced by electron-lattice interactions. Only ${\mathrm{C}\mathrm{u}}_{55}^{\ensuremath{-}}$ ${\mathrm{A}\mathrm{g}}_{55}^{\ensuremath{-}}$ exhibit highly...

Ground-state structures and other experimentally relevant isomers of Au(15) (-) to Au(24) clusters are determined through joint first-principles density functional theory photoelectron spectroscopy measurements. Subsequent calculations molecular O(2) adsorption the optimal cluster reveal a size-dependent reactivity pattern that agrees well with earlier experiments. A detailed analysis underlying electronic structure shows chemical gold anions can be elucidated in terms partial-jellium...

Melting temperatures of Na clusters show size-dependent fluctuations that have resisted interpretation so far. Here we discuss these temperatures, in fact, cannot be expected to exhibit an easily understandable behavior. The energy and entropy differences between the liquid solid turn out much more relevant parameters. They pronounced maxima correlate well with geometrical shell closings, demonstrating importance geometric structure for melting process. Icosahedral symmetry dominates, a...

Gold prospecting: Trapped-ion electron diffraction, photoelectron spectroscopy, and density functional theory are used to establish the structure of free gold cluster ion Au34−. The results suggest a chiral with an internal trigonal pyramid C3 point symmetry.

Magnetic spin and orbital moments of size-selected free iron cluster ions ${\mathrm{Fe}}_{n}^{+}$ ($n=3--20$) have been determined via x-ray magnetic circular dichroism spectroscopy. Iron atoms within the clusters exhibit ferromagnetic coupling except for $\mathrm{F}{\mathrm{e}}_{13}^{+}$, where central atom is coupled antiferromagnetically to in surrounding shell. Even very small clusters, moment strongly quenched reduced 5%--25% its atomic value while remains at 60%--90%. This demonstrates...

A new mass selection technique has been developed, which allows one to size-select charged particles from atoms nanoparticles of almost unlimited size. It provides a resolution m/Δm=20–50 and transmission about 50% for the selected size, both independent mass. The is based on time-of-flight principle, but differs fundamentally normally used. basic idea use time-limited high voltage pulses displace laterally preaccelerated ion beam, without changing its direction or shape. As movement ions...

We report the experimental structure determination of cold, mass selected Ag(55)(+/-) cluster ions using recently developed technique trapped ion electron diffraction. By comparison and theoretical molecular scattering functions consideration computed total energies, we show that Ag(55)(+) constitutes an ideal Mackay icosahedron, whereas Ag(55)(-) is a weakly Jahn-Teller distorted icosahedron. Isomers other structural types, for example, decahedral or close-packed, could be ruled out. The...

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 range n=20-120. A new isomer with a higher binding energy than so-called I has identified, which appears n=25-30 for becomes dominant at n=46. Magic numbers observed mass provide evidence that this class consists clusters an internal electron.

Size-selected cationic transition-metal-doped silicon clusters have been studied with x-ray absorption spectroscopy at the transition-metal ${L}_{2,3}$ edges to investigate local electronic structure of dopant atoms. For ${\text{VSi}}_{16}^{+}$, spectrum is dominated by sharp transitions which directly reveal formation a highly symmetric cage around vanadium atom. In spite their different number valence electrons, nearly identical found for atoms in ${\text{TiSi}}_{16}^{+}$, and...

We present an experimental study of the thermodynamics free, size-selected water cluster anions consisting 48 and 118 molecules. The measured caloric curves clusters are bulklike at low temperatures but show a well-defined, particle-size specific transition 93+/-3 K for (H2O)48- 118+/-3 (H2O)118-. At temperature heat capacity strongly increases, which marks onset melting.

Spin and orbital magnetic moments of cationic iron, cobalt, nickel clusters have been determined from x-ray circular dichroism spectroscopy. In the size regime $n=10--15$ atoms, iron cobalt show fully spin-polarized unoccupied $3d$ states with maximized spin $1\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{B}$ per hole because completely filled majority-spin bands. The notable exception is ${\mathrm{Fe}}_{13}^{+}$ where an unusually low average moment $0.73\ifmmode\pm\else\textpm\fi{}0.12$...

CrSin- (n = 14-18) cluster anions have been investigated by a combination of photoelectron spectroscopy (PES) and first-principles calculations. The lowest-lying structures the clusters determined global minimum search based on genetic algorithm, combined with density functional theory (DFT) simulated PES spectra lowest-energy isomers are in agreement experimental results, which gives strong evidence that correct found. While sizes n 14 15 prefer cage-like multi-center bonding within cage,...

We describe the construction and performance of a gas condensation cluster source. The source was designed for deposition mass-selected metal clusters with controlled landing energy. have produced Pbn (n=2–∼300) Agn (n=∼20–∼300) sufficient intensity to deposit size-selected density 1012 clusters/cm2 in 10 min. energy can be from ∼25 800 eV.

Photoabsorption cross sections for ${\mathrm{Ar}}_{\mathit{n}}^{+}$, 3\ensuremath{\le}n\ensuremath{\le}80, and ${\mathrm{Xe}}_{\mathit{n}}^{+}$, 3\ensuremath{\le}n\ensuremath{\le}30 clusters have been measured. A single absorption maximum in the visible is observed whose redshift with growing n interpreted as a delocalization of charge from trimer to tetramer ion. For ${\mathrm{Xe}}_{3}^{+}$, two maxima, n\ensuremath{\ge}5, three maxima are observed. n\ensuremath{\ge}5 positive can localize...

Optical absorption spectra for mass-selected ${\mathrm{Hg}}_{\mathit{n}}^{+}$ and ${\mathrm{Hg}}_{\mathit{n}}^{++}$ clusters show an abrupt transition to a collective, plasmonlike as function of increasing cluster size. The position the single observed plasmon maximum is independent charge state nearly peak positions agree well with those classical Mie calculated from experimental dielectric function. width resonance discussed strong temperature effect conjectured.

We have investigated the early stages of film growth via deposition size-selected silver clusters on graphite, as a function incident cluster size. For all sizes from 50 to 250 atoms per cluster, deposited are mobile and coalesce into three-dimensional particles with ‘‘universal’’ diameter ≊14 nm, possibly consequence lattice strain between graphite. The 14 nm found mainly in small aggregates, indicating that they themselves some degree mobile. also evidence particle mobility is influenced...

Sodium cluster anions Na(n)(-) with n = 39-350 have been studied by low temperature photoelectron spectroscopy and density functional theory (DFT). The highly structured experimental spectra are in excellent agreement the electronic of states (DOS) DFT lowest energy structures. Even for largest sizes, a pronounced sensitivity DOS on fine geometric details could be observed, allowing reliable identification specific icosahedral growth motif. intermediate sizes between closed-shell Mackay...

Although many properties of polyatomic metal clusters have been rationalized by an electron shell model resembling that used for free atoms, it remained unclear how reliable this analogy is with respect to the angular momentum eigenstate character electronic wave functions. We studied size-selected negatively charged sodium atoms (Na n – ) approximately spherical shape ( = 19, 40, 55, 58, 147) angle-resolved photoelectron spectroscopy over a broad range photon energies (1.5 5 volts). Highly...

An experiment was designed to perform x-ray and VUV spectroscopy on size-selected clusters in the gas phase. Using a radio frequency ion trap quadrupole mass filter combined with an intense magnetron sputter source made it possible record absorption spectra of mass-selected yield mode. These measurements clearly reveal development from richly structured atomic bulk-like line shapes transition metal clusters.