Planar oxide supported rhodium nanoparticles as model catalysts.

C(2)H(4)/CO/H(2) reaction is investigated on Rh/SiO(2) model catalyst surfaces. Kinetic reactivity and infrared spectroscopic measurements are investigated as a function of Rh particle size under near atmospheric reaction conditions. Results show that propionaldehyde turnover frequency (TOF) (CO insertion pathway) exhibits a maximum activity near = 2.

Characterization of active sites on Rh/SiO(2) model catalysts.

Rh/SiO(2) model catalyst surfaces are prepared under ultra-high vacuum conditions and examined in situ using scanning tunneling microscope and CO infrared reflection absorption techniques, to quantify the number and kinds of active Rh surface sites available for kinetic reaction (CO oxidation) as a function of Rh particle size. The results are compared against CO desorption measurements and elevated pressure CO oxidation reaction kinetics, to evaluate the extent of the correlation between the low and elevated pressure site characterization techniques. Data demonstrate that estimates of Rh active sites exhibit good agreement between the characterization methods and illustrate the utility of low pressure surface science characterization techniques in understanding elevated pressure reaction kinetics on model catalyst surfaces.

A dose dependence study of O(2) adsorbed on large Ar clusters.

An investigation of the behavior of O(2) molecules in and on O(2)-doped large (N approximately 8000) Ar host clusters has been performed by means of core and valence photoelectron spectroscopy. Data from pure O(2) and Ar clusters, as well as from O(2)-doped Ar clusters, are presented. The experimental data together with calculations of the binding energy shifts of oxygen molecular ions in and on the surface of a large host Ar cluster show that the diffusion behavior has a strong dependence on the doping pressure.

Localized versus delocalized excitations just above the 3d threshold in krypton clusters studied by Auger electron spectroscopy.

We present Auger spectroscopy studies of large krypton clusters excited by soft x-ray photons with energies on and just above the 3d(52) ionization threshold. The deexcitation spectra contain new features as compared to the spectra measured both below and far above threshold. Possible origins of these extra features, which stay at constant kinetic energies, are discussed: (1) normal Auger process with a postcollision interaction induced energy shift, (2) recapture of photoelectrons into high Rydberg orbitals after Auger decay, and (3) excitation into the conduction band (or "internal" ionization) followed by Auger decay.

Synchrotron radiation study of chloromethane clusters: effects of polarizability and dipole moment on core level chemical shifts.

Free neutral chloromethane clusters have been produced by adiabatic expansion and investigated by means of photoelectron spectroscopy. By studying the differences between the cluster binding energy shifts at the Cl 2p and C 1s thresholds we have shown that antiparallel packing is the dominant local structure of the clusters. This geometry is induced by the polar character of the constituent molecules, and it accords with the structures of chloromethane solids and dimers.