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131.
Wang JG Li WX Borg M Gustafson J Mikkelsen A Pedersen TM Lundgren E Weissenrieder J Klikovits J Schmid M Hammer B Andersen JN 《Physical review letters》2005,95(25):256102
Using core-level spectroscopy and density functional theory we show that a one-dimensional (1D) oxide structure forms at the steps of the Pt(332) surface after exposure. The 1D oxide is found to be stable in an oxygen pressure range, where bulk oxides are only metastable, and is therefore argued to be a precursor to the Pt oxidation. As an example of the consequences of such a precursor exclusively present at the steps, we investigate the reaction of CO with oxygen covered Pt(332). Albeit more strongly bound, the oxidic oxygen is found to react more easily with CO than oxygen chemisorbed on the Pt terraces. 相似文献
132.
Ackermann MD Pedersen TM Hendriksen BL Robach O Bobaru SC Popa I Quiros C Kim H Hammer B Ferrer S Frenken JW 《Physical review letters》2005,95(25):255505
We present the first structure determination by surface x-ray diffraction during the restructuring of a model catalyst under reaction conditions, i.e., at high pressure and high temperature, and correlate the restructuring with a change in catalytic activity. We have analyzed the Pt(110) surface during CO oxidation at pressures up to 0.5 bar and temperatures up to 625 K. Depending on the pressure ratio, we find three well-defined structures: namely, (i) the bulk-terminated Pt(110) surface, (ii) a thin, commensurate oxide, and (iii) a thin, incommensurate oxide. The commensurate oxide only appears under reaction conditions, i.e., when both and CO are present and at sufficiently high temperatures. Density functional theory calculations indicate that the commensurate oxide is stabilized by carbonate ions (CO3(2-)). Both oxides have a substantially higher catalytic activity than the bulk-terminated Pt surface. 相似文献
133.
Vestergaard EK Vang RT Knudsen J Pedersen TM An T Laegsgaard E Stensgaard I Hammer B Besenbacher F 《Physical review letters》2005,95(12):126101
The influence of high pressures of carbon monoxide (CO) on the stability of a Au/Ni(111) surface alloy has been studied by high-pressure scanning tunneling microscopy. We show that CO induces a phase separation of the surface alloy at high pressures, and by means of time-lapsed STM movies we find that Ni atoms are removed from the surface layer during the process. Density functional theory calculations reveal the thermodynamic driving force for the phase separation to be the Au-induced compression of the CO overlayer with a resulting CO-CO repulsion. Furthermore, the atomistic mechanism of the process is shown to be kink-site carbonyl formation and evaporation which is found to be enhanced by the presence of Au. 相似文献
134.
Precision measurements using the Rydberg charge-exchange and electric field-detachment methods find that the dipole-bound electron affinity (EA) of acetone (C3H6O) is 55+/-10 mueV greater than for deuterated acetone (C3D6O). The result agrees well with a theoretical prediction obtained with high-level electronic-structure and anharmonic vibrational calculations. The dipole moments calculated for the vibrationally averaged structures of C3H6O and C3D6O show that the isotope effect (2% reduction) on the EA of acetone is mainly due to a slight reduction (0.5%) of the average dipole moment upon deuteration. 相似文献
135.
Bland SN Lebedev SV Chittenden JP Ampleford DJ Bott SC Gómez JA Haines MG Hall GN Hammer DA Mitchell IH Palmer JB 《Physical review letters》2005,95(13):135001
The formation of plasma in wire-array Z-pinch experiments was found to depend upon the polarity of the radial-electric field near the wires. Reversing the radial-electric field midway along the length of an array resulted in the ablation rate of one-half of the array being reduced by 50%, significantly delaying the start of its implosion and altering its acceleration towards the axis. The observed phenomena cannot be explained by the standard magnetohydrodynamic models of array behavior, suggesting that effects such as electron emission may be important, especially during wire initiation. 相似文献
136.
An effective field theory for the three-body system with large scattering length is applied to three-body recombination to a weakly bound s-wave state in a Bose gas. Our model independent analysis demonstrates that the three-body recombination constant alpha is not universal, but can take any value between zero and 67.9Planck's over 2pia(4)/m, where a is the scattering length. Other low-energy three-body observables can be predicted in terms of a and alpha. Near a Feshbach resonance, alpha should oscillate between those limits as the magnetic field B approaches the point where a-->infinity. In any interval of B over which a increases by a factor of 22.7, alpha should have a zero. 相似文献
137.
Georg Albrecht Johann Wolfgang Hammer 《Zeitschrift für Physik A Hadrons and Nuclei》1975,273(4):405-410
TheK-fluorescence yieldΩ K of Titanium has been measured using the coincidence method and investigating the electron capture decay of48V. The detectors used have been a Si(Li)- and a Ge(Li)-detector for the X- andγ-rays. The experimental results areP K Ω K =0.2005 ±0.0030 andΩ K (Ti)=0.224±0.003 usingP K =0.896. For the branching ratios of the decay of48V we obtainedEC (3.239) 7.9±0.6%EC (3.224) 2.9±0.4%EC (2.295) 35.6±2.0% Β+ (2.295) 52±1.0% all others 1.6%. Additionally someγ-ray-energies of the decay of48V and the half-life,T 1 2=(16.23 ±0.03)d, have been measured. 相似文献
138.
S. Sterlinski W. Hammer M. Wasek 《Journal of Radioanalytical and Nuclear Chemistry》1987,114(2):243-255
The sources and nature of dead time of the multichannel analyzer (MCA) coupled to a Wilkinson type analog-to-digital converter (ADC) were examined. A dead time model based on two types of dead time, non-extended (nonparalysable) and extended (paralysable), is suggested. Special attention is paid to an extended type imposed by the pulse amplufier and the lower level discriminator in an ADC. 相似文献
139.
140.
Gerald Hammer 《Mathematische Zeitschrift》1963,81(5):395-413
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