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1.
T. Zabel M.E. Garcia K.H. Bennemann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(2):219-227
The absorption spectra of small Ag
+
n clusters are calculated at finite vibrational temperature by using a microscopic tight-binding RPA method. We consider free
clusters with sizes between n
= 3 and n
=13 and take into account explicitly the degrees of freedom corresponding to the 4
d-electrons. We analyze the optical absorption as a function of the cluster size. We show that the contribution of the d-electrons has an important influence on the size dependence of the energy of the Mie plasmon. We also perform ensemble averages
to obtain the absorption spectra for different vibrational temperatures. We obtain relatively good agreement with experiment
for a temperature . The dynamics of the 4
d-electrons, which shows in small clusters an incipient delocalized character for n
>7, yields an important contribution to the absorption spectrum already for n
=13. We find that the strength of this contribution can be controlled by varying the vibrational temperature.
Received: 4 January 1999 / Received in final form: 12 May 1999 相似文献
2.
V. Bonačić-Koutecký C. Bürgel L. Kronik A. E. Kuznetsov R. Mitrić 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):471-476
We present structural and optical properties of silver clusters Agn (n=2, 4, 6, 8) at two model support sites of MgO, stoichiometric MgO(100) and FS-center defect, based on density functional theory and embedded cluster model. Our results provide the mechanism responsible
for the absorption and emission patterns due to the specific interaction between the excitations
within the cluster and the support site which is strongly cluster size and structure dependent.
We propose Ag4 at stoichiometric site as well as Ag2, Ag4 and Ag6 at FS-center defects as good candidates for the emissive centers in the visible regime. 相似文献
3.
M. Bertolus V. Brenner P. Millié 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):387-394
An ab initio study of the Nan(OH)n, Nan(OH)n-1
+, Agn(OH)n, and Agn(OH)n-1
+ clusters with n up to four is presented. The results of this study show that, in accordance with experimental observations, the sodium hydroxide
clusters are almost purely ionic, while the Ag-O bond exhibits a significant covalent character. The perturbation caused by
the non-spherical OH- group relatively to an atomic anion, as well as the influence on structures and energies of the covalent character of the
metal-oxygen bond are determined. The appearance of metal-metal bonds in the silver hydroxide clusters is also discussed.
Finally, the theoretical results obtained on the Na-OH clusters are compared to experimental results available on the dissociation
of the Nan(OH)n-1
+ clusters.
Received 9 August 1999 and Received in final form 1st December 1999 相似文献
4.
Metastable fragmentation of silver bromide clusters 总被引:2,自引:0,他引:2
J.-M. L'Hermite F. Rabilloud L. Marcou P. Labastie 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):323-330
The abundance spectra and the fragmentation channels of silver bromide clusters have been measured and analyzed. The most
abundant species are AgnBrn - 1
+ and AgnBrn + 1
- and Ag14Br13
+ is a magic number, revealing their ionic nature. However, some features depart from what is generally observed for alkali-halide
ionic clusters. From a certain size, AgnBrn - 1
+ is no more the main series, and AgnBr n - 2, 3
+ series become almost as important. The fast fragmentation induced by a UV laser makes the cations lose more bromine than
silver ions and lead to more silver-rich clusters. Negative ions mass spectra contain also species with more silver atoms
than required by stoichiometry. We have investigated the metastable fragmentation of the cations using a new experimental
method. The large majority of the cations release mainly a neutral Ag3Br3 cluster. These decay channels are in full agreement with our recent ab initio DFT calculations, which show that Ag+-Ag+ repulsion is reduced due to a globally attractive interaction of their d orbitals. This effect leads to a particularly stable trimer (AgBr)3 and to quasi-planar cyclic structures of (AgBr)n clusters up to n = 6. We have shown that these two features may be extended to other silver halides, to silver hydroxides (AgOH)n, and to cuprous halide compounds.
Received 9 November 2000 and Received in final form 25 January 2001 相似文献
5.
V.Z. Cerovski S.D. Mahanti S.N. Khanna 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(1):119-122
Theoretical studies of the temperature (T) dependence of magnetization of Gd13 clusters have been carried out within a classical Heisenberg model using Monte-Carlo simulations. It is shown that for a
broad range of values of , defined as the ratio between competing ferro and anti-ferro magnetic couplings, the cluster magnetization increases with
T in the low T region, as seen in experiment. The clusters are also shown to exhibit a wide distribution of moments at a given T, which broadens significantly with increasing T. It is suggested that this may affect the observed magnetic behavior of magnetic clusters in Stern-Gerlach experiments.
Received 29 May 1999 and Received in final form 5 September 1999 相似文献
6.
Optical absorption of isolated silver cluster-tryptophan:
A joint experimental and theoretical study
T. Tabarin R. Antoine I. Compagnon M. Broyer P. Dugourd R. Mitrić J. Petersen V. Bonačić-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):275-278
We present a joint experimental and theoretical gas phase study of photoabsorption and photofragmentation of silver cluster-biomolecule
complexes. We demonstrate on the example of [ Trp.Ag3] + that binding of the metal cluster to a biomolecule leads to a significant enhancement of the photoabsorption in comparison
with [Trp.H]+ and [Trp.Ag]+. This enhancement arises due to the coupling between the excitations in the metallic subunit with charge transfer excitations
between silver cluster and tryptophan. Our experimental studies show that silver clusters up to eleven atoms can be bound
to tryptophan and we present first results on the photofragmentation of the Trp.Ag11
+ complex cation, in which properties of cluster subunit remain preserved. 相似文献
7.
V. Boutou A.R. Allouche F. Spiegelmann J. Chevaleyre M. Aubert Frécon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):63-73
The geometrical structure of ground state Ban clusters (n
=2-14) has been predicted from various types of calculations including two ab initio approaches used for the smaller sizes namely HF+MP2(
n
=2-6), DFT (LSDA)(
n
=2-6, 9) and one model approach HF+pairwise dispersion used for all sizes investigated here. The lowest energy configurations
as well as some isomers have been investigated. The sizes n
=4, 7 and 13 are predicted to be the relatively more stable ones and they correspond to the three compact structures: the tetrahedron,
the pentagonal bipyramid and the icosahedron. The growth behavior from Ba7 to Ba13 appears to be characterized by the addition of atoms around a pentagonal bipyramid leading to the icosahedral structure of
Ba13 which is consistent with the observed size-distribution of barium clusters. Values for vertical ionization potentials calculated
for n
=2-5 at the CI level are seen to be in quite good agreement with recent measures.
Received: 14 May 1997 / Received in final form: 2 February 1998 / Accepted: 27 February 1998 相似文献
8.
A. Herlert L. Schweikhard M. Vogel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):65-68
Singly charged silver-cluster anions are produced in a laser vaporization source and transferred into a Penning trap. After
size selection the clusters are subjected to an electron bath in the trap, which results in the attachment of further electrons.
The relative abundance of dianions or trianions as a function of the clusters' size is analyzed by time-of-flight mass spectrometry.
Silver-cluster dianions are observed for sizes n≥ 24 and trianions for n > 100. In addition, a detailed study of the cluster sizes 24 ?n? 60 shows a pronounced resistance to electron attachment for singly charged anions Agn
- with a closed electronic shell, in particular Ag29
-, Ag33
-, and Ag39
-. Both the threshold size for the observation of dianionic silver clusters and the shell effects in the production yield correlate
favorably with previous theoretical investigations of the respective electron affinities.
Received 24 November 2000 相似文献
9.
R. Mitri C. Bürgel J. Burda V. Bonai-Koutecký P. Fantucci 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):41-44
Bimetallic silver-gold clusters are well suited to study
changes in metallic versus
ionic properties involving charge transfer as a function of
the size and the composition. We present structures, ionization
potentials (IP) and vertical detachment energies (VDE) for
neutral and charged bimetallic
AunAgm (
2(n +
m)5) clusters obtained from
density functional level of theory. In the stable structures of
these clusters Au atoms assume positions which favor charge
transfer from Ag atoms. In clusters with equal numbers of hetero
atoms (n =
m = 1- 4) heteronuclear
bonding is preferred to homonuclear bonding, giving rise to
large values of ionization potentials. For larger clusters
(n=m=5, 10) stable structures do not favor
neither hetero bonding nor segregation into the single
components, although they exhibit more metallic than ionic
features. This remains valid also for
Au8Ag12 cluster
characterized by strong charge transfer to gold subunit. The
influence of doping of pure gold clusters with silver atoms on
VDE and IP values is discussed in context of their reactivity
towards O2 and CO molecules. As a
starting point we consider reactivity towards CO and
O2 molecules on the example of
AgAu- dimer. The results show that
the catalytic cycle can be fullfilled. 相似文献
10.
J. Zhao Y. Luo G. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):309-316
Tight-binding model is developed to study the structural and electronic properties of silver clusters. The ground state structures
of Ag clusters up to 21 atoms are optimized by molecular dynamics-based genetic algorithm. The results on small Agn clusters (n = 3-9) are comparable to ab initio calculations. The size dependence of electronic properties such as density of states, s-d band separation, HOMO-LUMO gap, and ionization potentials are discussed. Magic number behavior at Ag2, Ag8, Ag14, Ag18, Ag20 is obtained, in agreement with the prediction of electronic ellipsoid shell model. We suggest that both the electronic and
geometrical effect play significant role in the coinage metal clusters.
Received 7 August 2000 相似文献
11.
M.-H. Schaffner F. Patthey U. Heiz W.-D. Schneider O. Kuffer H.-V. Roy P. Fayet J.K. Gimzewski R. Berndt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):79-82
The emission of photons in the visible wavelength range from mass-selected Ag+
n, Cu+
n, Pt+
n and Pd+
n () clusters is observed. Photons are detected 10-4 s after the cluster generation in a sputter source. The emission intensities display distinct variations with cluster size
and material. The observations are interpreted in terms of the decay of metastable states which are excited during the high-energy
sputtering process used for the generation of these clusters.
Received: 28 October 1997 / Revised: 5 January 1998 / Accepted: 30 January 1998 相似文献
12.
13.
A. Miotello G. De Marchi G. Mattei P. Mazzoldi A. Quaranta 《Applied Physics A: Materials Science & Processing》2000,70(4):415-419
The diffusional growth regime of silver clusters in hydrogenated silver–sodium exchanged glasses has been numerically analysed.
The diffusion coefficients of the three elements that contribute to silver cluster formation, namely H, Ag+, and Ag0, have been established. The activation energy of the reactant Ag0 diffusion coefficient is consistent in the three analysed different experimental results: Ag loss through evaporation, near-surface
Ag accumulation, and optical absorption density. The calculated Ag0 diffusion coefficient accounts for the threshold time necessary to obtain a cluster size to give rise to a detectable absorption.
Received: 27 September 1999 / Accepted: 11 October 1999 / Published online: 8 March 2000 相似文献
14.
D.J. Kenny S.C. Weller M. Couillard R.E. Palmer C.F. Sanz-Navarro R. Smith 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):115-118
Scanning tunnelling microscopy (STM) and molecular dynamics (MD) simulations have been used to investigate the implantation
of Ag7
- clusters into the graphite surface. An experimental measure of the implantation depth of individual clusters is gained via thermal oxidation of the bombarded graphite surfaces. This process results in etching of the cluster-induced defects to form
etch pits which grow laterally whilst retaining the depth of the implanted cluster. STM imaging of the etch pits reveals the
distribution of implantation depths for deposition energies of 2 keV and 5 keV. Molecular dynamics simulations for clusters
of 5 keV energy show that the implantation depth for Ag7
- is largely independent of the impact site on the graphite surface and the cluster orientation. The implantation depth found
by MD lies at the upper edge of the experimental depth distribution.
Received 30 November 2000 相似文献
15.
A comparative study on geometries,stabilities, and electronic properties between bimetallic AgnX(X=Au,Cu;n=1-8)and pure silver clusters 下载免费PDF全文
Using the meta-generalized gradient approximation (meta-GGA) exchange correlation TPSS functional, the geo- metric structures, the relative stabilities, and the electronic properties of bimetallic Ag n X (X=Au, Cu; n=1–8) clusters are systematically investigated and compared with those of pure silver clusters. The optimized structures show that the transition point from preferentially planar to three-dimensional structure occurs at n = 6 for the Ag n Au clusters, and at n = 5 for Ag n Cu clusters. For different-sized Ag n X clusters, one X (X=Au or Cu) atom substituted Ag n+1 structure is a dominant growth pattern. The calculated fragmentation energies, second-order differences in energies, and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gaps show interesting odd–even oscillation behaviours, indicating that Ag 2,4,6,8 and Ag 1,3,5,7 X (X=Au, Cu) clusters keep high stabilities in comparison with their neighbouring clusters. The natural population analysis reveals that the charges transfer from the Ag n host to the impurity atom except for the Ag 2 Cu cluster. Moreover, vertical ionization potential (VIP), vertical electronic affinity (VEA), and chemical hardness (η) are discussed and compared in depth. The same odd–even oscillations are found for the VIP and η of the Ag n X (X=Au, Cu; n=1–8) clusters. 相似文献
16.
M. Hartmann R. Mitrić B. Stanca V. Bonačić-Koutecký 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):151-155
Ultrafast ground state nuclear dynamics of Au4 and Ag4 is theoretically explored in the framework of negative ion - to neutral - to positive ion (NeNePo) pump-probe spectroscopy
based on the ab initio Wigner distribution approach. This involves the preparation of a nonequilibrium neutral ensemble by pump induced photodetachment
of a thermal anionic ground state distribution, gradient corrected DFT classical trajectory simulations “on the fly” on the
neutral ground state, and detection of the relaxation process of the ensemble in the cationic ground state by a time-delayed
probe pulse. In Au4, the initially prepared linear structure is close to a local minimum of the neutral state giving rise to characteristic vibrations
in the signals for probe wavelength near the initial Franck-Condon transition. A timescale of ∼1 ps for the structural relaxation towards the stable rhombic D2h neutral isomer was determined by the increase of the signal for probe wavelength in vicinity of the vertical ionization energy
of the rhombic structure. In contrast, the relaxation dynamics in Ag4 is characterized by normal mode vibrations since both the initially prepared anionic ground state and the neutral ground
state have rhombic minimum geometries. Thus, time-resolved oscillations of pump-probe signals are fingerprints of structural
behaviour which can be used experimentally for the identification of particular isomers in the framework of NeNePo spectroscopy.
Received 22 December 2000 相似文献
17.
E. Cottancin M. Gaudry M. Pellarin J. Lermé L. Arnaud J. R. Huntzinger J. L. Vialle M. Treilleux P. Mélinon J.-L. Rousset M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):111-114
The optical properties of mixed
(Ni0.5Ag0.5)n
and Pt/Ag clusters are investigated in the size range 2-5 nm.
Low Energy Ion Spectroscopy (LEIS) experiments show that the
cluster surface is entirely covered by silver atoms for the two
systems. The optical spectra of Ni/Ag clusters exhibit a large
Surface Plasmon Resonance (SPR), damped and widened when the
cluster size decreases, in agreement with a classical model
assuming a core-shell geometry and including the reduction of
the conduction electron mean-free path in the silver shell. For
Pt/Ag clusters, no SPR emerges in the size range 2-5 nm,
although it is predicted within a classical model, a pronounced
SPR appearing only for clusters larger than 10 nm in diameter. 相似文献
18.
G. Chen Z.F. Liu X.G. Gong 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):33-36
We have studied the atomic structure and the electronic properties of Ban clusters by the ab initio molecular dynamics method. We find that a structural transition to the bulk-like structure begins at Ba9 cluster, and the structures of the clusters are transferred to be icosahedral-like around n
= 13. The relatively high stability for Ba4, Ba10 and Ba13 clusters are observed.
Received 1st December 2000 相似文献
19.
T.M. Di Palma A. Latini M. Satta A. Giardini-Guidoni 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(2):225-229
A photoionization study of the Me(NH3) clusters formed in the reaction of photoablated third group metal vapor with gaseous ammonia is reported. The photoionization
spectra exhibit some features due to vibrational excitation of ionic clusters and to transitions to neutral Rydberg states
leading to autoionization. DFT quantum chemical calculations are performed on the Me(NH3). The cluster geometries are fully optimized imposing the C3v symmetry. The calculated values of the IPs are in agreement with those experimentally determined.
Received: 16 February 1998 / Revised and Accepted: 7 May 1998 相似文献
20.
G. Durand F. Spiegelman A. R. Allouche 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):19-22
Recently, electric susceptibilities of
NanFn-1 clusters
have been measured by deflecting a molecular beam in an
inhomogeneous electric field. The analysis of the deflection of
a cluster by the electric field needs the calculation of the
electric properties. We present the calculation of the static
anisotropic and average dipolar polarizabilities within a model
in which the
NanFn-1 clusters (
2
n
23)
are treated as one electron embedded in the field of
n ions
Na+ and of n
- 1
ions F-. The accuracy of the results
is evaluated and discussed on small clusters (n
5)
in comparison with ab initio
calculations. The relationship between the polarizabilities, the
electronic localization and the geometric structure is
discussed. Received 10 September 2002 Published online 3 July
2003 相似文献