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991.
Dr. Francesc Viñes Prof. Dr. Andreas Görling 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(50):11478-11491
Cu@Pt nanoparticles (NPs) are experimentally regarded as improved catalysts for NOx storage/reduction, with higher activities and selectivities compared with pure Pt or Cu NPs, and with inverse Pt@Cu NPs. Here, a density functional theory-based study on such NP models with different sizes and shapes reveals that the observed enhanced stability of Cu@Pt compared with Pt@Cu NPs is due to energetic reasons. On both types of core@shell NPs, charge is transferred from Cu to Pt, strengthening the NP cohesion energy in Pt@Cu NPs, and spreading charge along the surface in Cu@Pt NPs. The negative surface Pt atoms in the latter diminish the NO bonding owing to an energetic rise of the Pt bands, as detected by the appliance of the d-band model, although other factors, such as atomic low coordination or the presence of an immediate subsurface Pt atom do as well. A charge density difference analysis discloses a donation/back-donation mechanism in the NO adsorption. 相似文献
992.
The first catalytic asymmetric formation of a fulvene from a racemic α,α-disubstituted aldehyde has been developed. Dynamic kinetic resolution of rac-2-phenylpropanal by a simple, modularly designed supramolecular organocatalyst consisting of inexpensive components has been established, producing the desired fulvene in good yields and moderate enantioselectivities. Herein we propose a mechanistic interpretation of the observed solvent- and additive-induced stereoselectivity reversal. 相似文献
993.
Accreditation and Quality Assurance - 相似文献
994.
995.
996.
The dynamic Stark effect of the spectral lines Hβ and of the neutral helium lines λ=402.6 nm (23
P
0−53
D) and λ=438.8 nm (21
P
0−51
D) emitted from a discharge tube was used for probing rf electric fields in a transverse waveguide. Calculations accounting
for the pertubation of the atomic states by strong unidirectional fields prove to be suitable in order to interprete the main
experimental results. If the waveguide is terminated with a metallic reflector and the plasma in the discharge tube becomes
overdense—then representing a slightly permeable mirror—a resonant enhancement of the electric field strength may be achieved
by tuning. This enhancement is well recognizable in the spectral line contours. 相似文献
997.
J.F. van der Veen F.J. Himpsel D.E. Eastman P. Heimann 《Solid State Communications》1980,36(2):99-104
Using a display-type analyzer, we have measured the angular and energy distribution of O+ ions desorbed from a V2O5(010) surface by incident photons. The desorbed ions were mass-analyzed using time-of-flight gating techniques. The angular distribution of desorbed ions was found to be strongly peaked in the direction of the surface normal. This strongly directional desorption pattern reflects the local bonding geometry of the topmost oxygen atoms in the surface. The observed photoexcitation spectrum of the ion yiel can be explained with the core level Auger decay model formulated by Knotek and Feibelman. 相似文献
998.
Reflectivity spectra of CuInSe2, CuInTe2 and CuGaTe2 are measured in the photon energy range from 2 to 9 eV. All compounds exhibit nearly the same reflectivity structures, and a comparison with measurements on the other Cu-III-VI2 semiconductors shows that the band structures of all Cu-III-VI2 compounds should be very similar except the energy range near the fundamental edge. 相似文献
999.
The proton spin-lattice relaxation times, T1, of methyl groups in (CH3CO)2O, CH3COCl, CH3 COBr and (CH3)2S2 have been measured below melting points at 52 MHz. The observed T1 minima display the presence of tunnelling rotation. From the fit of the experimental results the ground, the first excited state tunnelling frequencies and the energy difference between the ground and the first excited states of the compounds have been estimated. 相似文献
1000.
We find a quasi quadratic dispersion of the plasmon up to
p
= 28 eV atk=1.77 Å–1 with no levelling off contrary to other measurements. We usedk-scans at constant energy loss andE-scans at constant wave vector, which yield different dispersions of the plasmon peak maximum because of the finite halfwidth. The levelling off in plasmon dispersion observed previously is due to multiple scattering events, which obscure the plasmon dispersion inE-scans.We confirmed the anisotropy of the dispersion coefficient by investigating polycrystalline samples of different orientation. 相似文献