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  • 1
    Electronic Resource
    Electronic Resource
    Ultraviolet photoelectron spectroscopy of copper clusters (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5377-5382 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a new magnetically focused time-of-flight photoelectron spectrometer, the ultraviolet photoelectron spectra (UPS) of mass-selected negative copper clusters have been measured at photon energy of 4.66 eV for all clusters in the range from 6 through 41 copper atoms. These UPS data provide the first detailed probe of the 4s valence band structure of such medium size negative copper clusters, and extend previous approximate measures of the electron affinity of the corresponding neutral species. The results are in accord with the predictions of the ellipsoidal shell model for monovalent metal clusters. In particular, clusters 8, 20, and 40 (which correspond to spherical shell closings in this simple model) are found to have unusually low electron affinities and large HOMO–LUMO gaps. Subshell closings at 14 and 34 also appear special in this new UPS data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454575
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  • 2
    Electronic Resource
    Electronic Resource
    Fourier transform ion cyclotron resonance studies of H2 chemisorption on niobium cluster cations (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5215-5224 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reaction rates and saturation values were determined for H2 dissociative chemisorption on positive niobium cluster ions in an FT-ICR apparatus. Clusters with 8,10,12, and 16 atoms were found to be particularly unreactive, in remarkable agreement with the reactivity patterns observed previously for neutral niobium clusters. Saturation coverage for most clusters was found to occur near a hydrogen/niobium ratio of 1.3, although some clusters (8–12,16, and 19) reached effectively inert compositions at considerably lower coverages. Several examples were found of clusters having two isomeric forms with different reactivities. One form of Nb+19 was found to readily react with H2, whereas a second form representing one-third of the original sample of 19 atom clusters was completely inert to H2 chemisorption under the same FT-ICR conditions. The geometrical shape of these niobium clusters must therefore have a critical effect on reactivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454596
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  • 3
    Electronic Resource
    Electronic Resource
    Ammonia chemisorption studies on silicon cluster ions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2618-2630 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Silicon clusters in the size range from 5 to 66 atoms were generated by laser vaporization in a supersonic nozzle and injected into the ion trap of a specially-designed Fourier transform ion cyclotron resonance apparatus. On the positively charged clusters ammonia chemisorption reaction rates were found to vary by over three orders of magnitude as a function of cluster size, with clusters of 21, 25, 33, 39, and 45 atoms being particularly unreactive, and cluster 43 being the most reactive. For the negative cluster ions, 43 was the only cluster found to react substantially. Although the reaction behavior of many clusters clearly indicated that several structural isomers were present with different reaction rates, the strikingly low net reactivity of such clusters as 39 and 45 provides evidence that they have effectively crystallized into a single specially stable form.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459838
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic structure of small GaAs clusters (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8015-8020 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic structure of small GaxAsy clusters (x+y≤10) are calculated using the local density method. The calculation shows that even-numbered clusters tend to be singlets, as opposed to odd-numbered clusters which are open shell systems. This is in agreement with the experimental observations of even/odd alternations of the electron affinity and ionization potential. In the larger clusters, the atoms prefer an alternating bond arrangement; charge transfers are observed from Ga sites to As sites. This observation is also in agreement with recent chemisorption studies of ammonia on GaAs clusters. The close agreement between theoretical calculations and experimental results, together with the rich variation of electronic properties of GaAs clusters with composition makes GaAs clusters an ideal prototype system for the study of how electronic structure influences chemical reactivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460135
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  • 5
    Electronic Resource
    Electronic Resource
    Supersonic cluster source with mass selection and energy control (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2267-2275 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have developed an apparatus that produces an ionized beam of mass selected clusters of controllable energy. It uses a pulse of second-harmonic light from a Nd:YAG laser to vaporize atoms from a target disk. The clustering rate of the atoms in this expanding plume is controlled with the pressure of a He pulse injected from a fast pulsed valve. A Wiley–McLaren type time-of-flight mass spectrometer with a shield lens is used to monitor the cluster distribution and to optimize the control parameters of the system. The shield lens doubles the resolution and the signal-to-noise ratio of the spectrometer. A 4000 amu rf quadrupole with 1.2 amu resolution is used to select the mass of charged clusters. An electrostatic quadrupole is used to separate the charged clusters from the neutral clusters and the He gas. The ionized clusters are then focused onto a suitably prepared substrate by using electrostatic lenses. Time averaged deposition current densities on the order of 100 pA cm−2 have been measured when the vaporization laser is fired at 10 Hz. The deposition energy of the clusters is controlled by applying a bias voltage to the substrate. A mobile vacuum chamber is used to transfer samples to various diagnostic systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144675
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Dissociative chemisorption of molecular hydrogen on niobium cluster ions. A supersonic cluster beam FT-ICR experiment (1986)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 90 (1986), S. 4480-4482 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100410a004
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  • 7
    Electronic Resource
    Electronic Resource
    FT-ICR probes of silicon cluster chemistry: The special behavior of Si+39 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2397-2399 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: FT-ICR techniques were used to probe the surface chemistry of isolated silicon cluster ions in the 7–65 atom size range. Dissociative chemisorption reactions with NH3 were observed to proceed with rates which varied widely with cluster size. One particular cluster, Si+39, was found to be remarkably inert. Clusters with 20, 25, 33, and 45 atoms were found to be unreactive as well, while those with 18, 23, 30, 36, 43, or 46 atoms were quite reactive. Similarly oscillating reaction patterns were observed with CH3OH, whereas highly reactive free radical scavengers such as O2 and NO showed little selectivity. These results suggest the silicon clusters in this size range have well-defined structures which vary in ability to catalyze dissociative chemisorption at the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453123
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