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11.
Niemeyer M Hirsch K Zamudio-Bayer V Langenberg A Vogel M Kossick M Ebrecht C Egashira K Terasaki A Möller T Issendorff BV Lau JT 《Physical review letters》2012,108(5):057201
Magnetic spin and orbital moments of size-selected free iron cluster ions 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 Fe{13}{+}, where the central atom is coupled antiferromagnetically to the atoms in the surrounding shell. Even in very small clusters, the orbital magnetic moment is strongly quenched and reduced to 5%-25% of its atomic value while the spin magnetic moment remains at 60%-90%. This demonstrates that the formation of bonds quenches orbital angular momenta in homonuclear iron clusters already for coordination numbers much smaller than those of the bulk. 相似文献
12.
Protonated water clusters with 60 to 79 molecules have been studied by nanocalorimetry. The technique is based on multi-collision excitations of the accelerated clusters with helium. The caloric curves indicate transitions that resemble those of water clusters charged by an excess electron, but the transition temperatures of the protonated clusters are higher. 相似文献
13.
14.
H. Haberland B. v. Issendorff R. Fröchtenicht 《Zeitschrift für Physik B Condensed Matter》1995,98(3):417-419
Ionized argon clusters were generated by electron impact ionization of neutral argon clusters embedded in large neutral helium clusters. Photofragmentation spectroscopy of Ar
3
+
and Ar
3
+
He produced in this way demonstrates the strong influence of vibrational excitation on the photodissociation dynamics, and indicates the low internal energy of the latter cluster. 相似文献
15.
16.
S. Duffe T. Irawan M. Bieletzki T. Richter B. Sieben C. Yin B. von Issendorff M. Moseler H. Hövel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):401-408
The low energy deposition of silver cluster cations with
561 (±5) atoms on a cold fullerene covered gold surface has
been studied both by scanning tunneling microscopy and molecular
dynamics simulation. The special properties of the
C60/Au(111) surface result in a noticeable fixation of the
clusters without a significant change of the cluster shape. Upon
heating to room temperature we observe a flattening or shrinking
of the cluster samples due to thermal activation. Similar changes were observed also for mass selected Ag clusters with other
sizes. For comparison
we also studied Ag islands of similar size, grown by low
temperature deposition of Ag atoms and subsequent annealing. A
completely different behavior is observed with much broader size
distributions and a qualitatively different response to
annealing. 相似文献
17.
Prabal Talukdar F. V. Issendorff D. Trimis C. J. Simonson 《Heat and Mass Transfer》2008,44(6):695-704
Interaction of conduction and radiation in 3D enclosures is carried out with a gray participating media. Application of block
structured grid is shown with the finite volume method (FVM). Radiation modeling is performed with the FVM and is coupled
with an ‘in-house’ code to solve the set of transport equations. The detailed numerical results are presented for a cubical
and a cylindrical enclosure as these results are not available in the literature. The numerical simulation for the cylindrical
enclosure is performed using a block-structured ‘O’ grid. Two additional geometries are considered in order to show the applicability
of the present work. Results of temperature, radiative heat flux and total heat flux distributions are presented for different
optical thicknesses, scattering albedoes, emissivities and conduction–radiation parameters. The 3D results are validated with
the available 2D results or results with pure radiation problems as limiting cases. 相似文献
18.
Haberland H Hippler T Donges J Kostko O Schmidt M von Issendorff B 《Physical review letters》2005,94(3):035701
Melting temperatures of Na clusters show size-dependent fluctuations that have resisted interpretation so far. Here we discuss that these temperatures, in fact, cannot be expected to exhibit an easily understandable behavior. The energy and entropy differences between the liquid and the solid clusters turn out to be much more relevant parameters. They exhibit pronounced maxima that correlate well with geometrical shell closings, demonstrating the importance of geometric structure for the melting process. Icosahedral symmetry dominates, a conclusion corroborated by new photoelectron spectra measured on cold cluster anions. In the vicinity of the geometrical shell closings the measured entropy change upon melting is in good agreement with a simple combinatorial model. 相似文献
19.
Negative heat capacity for a cluster of 147 sodium atoms 总被引:10,自引:0,他引:10
Schmidt M Kusche R Hippler T Donges J Kronmüller W von Issendorff B Haberland H 《Physical review letters》2001,86(7):1191-1194
There exists a surprising theoretical prediction for a small system: its microcanonical heat capacity can become negative. An increase of energy can-under certain conditions-lead to a lower temperature. Here we present experimental evidence that a cluster containing exactly 147 sodium atoms does indeed have a negative microcanonical heat capacity near its solid to liquid transition. 相似文献
20.
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 with the electronic density of states (DOS) of the DFT lowest energy structures. Even for the largest sizes, a pronounced sensitivity of the DOS on fine geometric details could be observed, allowing for a reliable identification of a specific icosahedral growth motif. The intermediate sizes between the closed-shell Mackay clusters with 55, 147, and 309 atoms form by growth of overlayers, which often exhibit a twist deformation with respect to regular (Mackay-type) ones. 相似文献