共查询到20条相似文献,搜索用时 15 毫秒
1.
M. Gaudry J. Lermé E. Cottancin M. Pellarin B. Prével M. Treilleux P. Mélinon J.-L. Rousset M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):201-204
Optical properties of mixed clusters (AuxAg
1 - x
)
n
and (NixAg
1 - x
)
n
, produced by laser vaporization and embedded in an alumina matrix, are reported. The size effects are investigated for different
concentrations (x
= 0.25, 0.5 and 0.75) in the diameter range 2-4 nm. For alloyed clusters (AuxAg
1 - x
)
n
of a given size an almost linear evolution of the surface plasmon frequency ω
s
with the concentration is observed (between those of pure gold and pure silver clusters). Moreover the blue-shift and the
damping of the resonance with decreasing size is all the more important as the gold concentration in the particles increases.
Such results are in agreement with theoretical calculations carried out in the frame of the time-dependent local-density-approximation
(TDLDA) including an inner skin of ineffective screening and the porosity of the matrix. The optical response of (NixAg
1 - x
)
n
clusters exhibits a surface plasmon resonance in the same spectral range as the one observed for pure silver clusters, but
considerably damped and broadened. For a given mean cluster size 3.0 nm, a blue-shift of the resonance is observed when increasing
the nickel concentration (between x
= 0.25 and x
= 0.75). The results are in good qualitative agreement with classical predictions in the dipolar approximation, assuming a core-shell
geometry.
Received 21 November 2000 相似文献
2.
M. Vogel K. Hansen A. Herlert L. Schweikhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):73-76
The decay pathway competition between monomer and dimer evaporation of photoexcited cluster ions Au
+
n, n = 2-27, has been investigated by photodissociation of size-selected gold clusters stored in a Penning trap. For n > 6 the two decay pathways are distinguished by their experimental signature in time-resolved measurements of the dissociation.
For the smaller clusters, simple fragment spectra were used. As in the case of the other copper-group elements, even-numbered
gold cluster ions decay exclusively by monomer evaporation, irrespective of their size. For small odd-size gold clusters,
dimer evaporation is a competitive alternative, and the smaller the odd-sized clusters, the more likely they decay by dimer
evaporation. In this respect, Au
+
9 shows an anomalous behavior, as it is less likely to evaporate dimers than its two odd-numbered neighbors, Au
+
7 and Au
+
11. This nonamer anomaly is typical for copper-group cluster ions M
+
9 (M = Cu, Ag, Au) and a similar behavior is found in the anionic heptamers M
-
7. It is discussed in terms of the well-known electronic shell closing at n
e = 8 atomic valence electrons.
Received 2 November 2000 相似文献
3.
M.A. Gaveau M. Briant P.R. Fournier J.M. Mestdagh J.P. Visticot F. Calvo S. Baudrand F. Spiegelman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):153-161
Spectroscopic experiments have been performed, providing emission and excitation spectra of calcium atoms trapped on argon
clusters of average size 2 000. The two experimental spectra fall in the vicinity of the calcium resonance line 1P 1 → 1S0 at 422.9 nm. The excitation spectrum consists in two bands located on each side of the resonance line of the free calcium.
In addition, Monte Carlo calculations, coupled to Diatomics-In-Molecule potentials are employed to simulate the absorption
spectrum of a single calcium atom in the environment of a large argon cluster of average size 300. The theoretical absorption
spectrum confirms the existence of two bands, and shows that these bands are characteristic of a calcium atom located at the
surface of the argon cluster and correspond to the excited 4p orbital of calcium either perpendicular or parallel to the cluster surface. The precise comparison between the shape of the
absorption spectrum and that of the fluorescence excitation spectrum shows different intensity ratios. This could suggest
the existence of a non adiabatic energy transfer that quenches partly the fluorescence of trapped calcium. Another explanation,
although less likely, could be a substantial dependence of the calcium oscillator strength according to the alignment of the
calcium excited orbital with respect to the cluster surface. The emission spectrum always shows a band in the red of the resonance
line which is assigned to the emission of calcium remaining trapped on the cluster. When exciting the blue band of the excitation
spectrum, the emission spectrum shows a second, weak, component that is assigned to calcium atoms ejected from the argon clusters,
indicating a competition between ejection and solvation.
Received 7 May 2002 Published online 1st October 2002
RID="a"
ID="a"e-mail: jmm@drecam.saclay.cea.fr
RID="b"
ID="b"URA 2453 du CNRS
RID="c"
ID="c"UMR 5626 du CNRS 相似文献
4.
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
5.
Systematic study of small BN clusters 总被引:2,自引:0,他引:2
S. Guerini P. Piquini 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):17-20
We performed a systematic investigation of the small BxNy (x + y? 6) clusters using the ab initio Hartree-Fock scheme plus second-order perturbation theory. The nature of the potential energy surface extrema are analyzed
through analytical total energy second derivatives. Ionization potentials, binding energies and the stability against some
possible reaction mechanisms are calculated. Based on these results we propose that the growing process for these clusters
is mainly due to the successive incorporation of BN molecules. A discussion of some mass spectrometry experimental results
is also presented.
Received 2 October 2000 相似文献
6.
G. Durand F. Spiegelmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):237-243
The stability against fragmentation and possible relaxation of the lowest excited states of the Na5F4 cluster (representative of cubic non stoechiometric clusters with an excess sodium atom, also called sodium-tail) is investigated
by means of one-electron pseudopotential calculations with particular reference to photoabsorption processes from the ground
state. Whereas the equilibrium configuration of the ground state has C3v symmetry, the doubly degenerate 12E excited state is affected by a conical intersection and a Jahn-Teller effect associated with the rotation of the sodium
tail around the C3-axis. This yields a “Mexican hat" topology for the lowest sheet with three equivalent Cs minima. Alternatively the 22A1 state has a minimum retaining the C3v symmetry. The dissociation paths of the cluster along the C3-axis into respectively Na4F4 + Na and Na4F3 + NaF are also investigated. Among the former paths, the excited states are found adiabatically stable with respect to the
products. However in the A1 symmetry, fragmentation into NaF exhibits an interesting avoided crossing between configurations correlated respectively
with Na4F3
+ + NaF- and Na4F3 + NaF. Such interaction, similar to the well-known charge exchange processes in elementary molecules might induce non adiabatic
predissociation of the 22A1 state. This mechanism is invoked to explain the differences between R2PI and depletion spectra, correlated with the dissociation
or relaxation of the excited states.
Received 24 March 2000 and Received in final form 11 July 2000 相似文献
7.
K. Ohshimo H. Tsunoyama F. Misaizu K. Ohno 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):107-110
Intracluster electron transfer and oligomerization reaction were investigated by mass spectrometry of clusters of alkali metal
atom (M) with acrylonitrile (AN; CH2=CHCN). In the photoionization mass spectra of M(AN)n, magic numbers were clearly observed at n = 3k (k = 1-4 for M = Na and K, k = 1 for M = Li). The results of photodissociation of neutral K(AN)n indicate that the n = 3 cluster has an anomalous stability relative to other sizes of clusters. The C=C bond in vinyl molecules is also found
to be necessary to form the magic numbers by measuring the photoionization mass spectrum of K atom with propionitrile. These
results strongly support the intracluster anionic oligomerization reaction initiated by electron transfer from the alkali
atom. The quantum chemical calculations have revealed that the evaporation induced by excess energy generated by intracluster
oligomerization is important to form the magic numbers in the present clusters.
Received 29 November 2000 相似文献
8.
C. Herwig J.A. Becker 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):51-54
The growth of small tellurium clusters in helium and the influence of a metal impurity (dysprosium atoms) on the cluster size
distribution are investigated in a double laser vaporization source. A model describing the role of the carrier gas as collision
partner is presented, emphasizing the crucial influence of the gas pressure on cluster formation. Changes in cluster reactivity
due to dysprosium addition are discussed in terms of ionic structures Dy
3 +(Te
N)3 - containing a radical electron.
Received 28 November 2000 相似文献
9.
K. Hamada T. Wada C. Guet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):359-368
Stability of highly charged metal clusters in the electric field of an external ion is investigated with the classical liquid
drop model. We study the optimum shape of the cluster which has a local minimum of the total energy, taking account of the
effects of the surface charge polarization on the Coulomb energy and the cluster deformation on the surface energy. We find
that the cluster deformation greatly affects the total energy of the system and that a cluster with a fissility larger than
some critical value 0.7-0.8 can become unstable against deformation. We investigate the local competition between the Coulomb
force and the surface tension at the cluster surface and show that the surface charge polarization which is induced by the
external electric field significantly affects the shape of the cluster and its stability.
Received 5 November 2002 / Received in final form 27 January 2003 Published online 11 March 2003
RID="a"
ID="a"e-mail: hamada@konan-u.ac.jp 相似文献
10.
R. von Pietrowski K. von Haeften T. Laarmann T. Möller L. Museur A. V. Kanaev 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):323-336
The electronic and geometric structure of rare gas clusters doped with
rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation
spectroscopy in the VUV spectral range. Several absorption bands are
observed in the region of the first electronic excitations of the impurity
atoms, which are related to the lowest spin-orbit split atomic 3P1
and 1P1 states. Due to influence of surrounding atoms of the
cluster, the atomic lines are shifted to the blue and broadened
(“electronical cage effect”). From the known interaction potentials and
the measured spectral shifts the coordination of the impurity atom in
ArN, KrN, NeN and HeN could be studied in great detail.
In the interior of KrN and ArN the Xe atoms are located in
substitutional sites with 12 nearest neighbours and internuclear distances
comparable to that of the host matrix. In NeN and HeN the cluster
atoms (18 and 22, respectively) arrange themselves around the Xe impurity
with a bondlength comparable to that of the heteronuclear dimer. The results
confirm that He clusters are liquid while Ne clusters are solid for N≥
300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is
strong, small Rgm-clusters (Rg = Xe, Kr, Ar, m≤10 2) are formed
in the interior sites of the host cluster made of Ne or He. Specific
electronically excited states, assigned to interface excitons are observed.
Their absorption bands appear and shift towards lower energy when the
cluster size m increases, according to the Frenkel exciton model. The
characteristic bulk excitons appear in the spectra, only when the cluster
radius exceeds the penetration depth of the interface exciton, which can be
considerably larger than that in free Rgm clusters. This effect is
sensitive to electron affinities of the guest and the host cluster. 相似文献
11.
D. Blume Chris H. Greene 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):83-86
We analyze various microscopic calculations of vibrational frequencies for 4HeN clusters, N = 3-728. The lowest breathing frequency with total angular momentum J = 0 varies smoothly as a function of N, with a maximum around N = 50-120.
Received 11 July 2001 相似文献
12.
Solcà N. Dopfer O. 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):469-480
Infrared (IR) photodissociation spectra of the aniline+-Arn cations, An
+
-
Ar
n
(n
= 1, 2), are analyzed in the vicinity of the N-H stretch fundamentals. The complexes are produced in an electron impact (EI) ion
source which produces predominantly the most stable cluster isomers. Two isomers of An+-Ar are identified by their characteristic N-H stretch frequencies: the planar proton-bound global minimum, in which the Ar
ligand forms a nearly linear H-bond to the amino group, and the less stable π-bound local minimum, in which the Ar atom is attached to the π-electron system of the aromatic ring. This result is the first unambiguous detection of the most stable H-bound An+-Ar dimer. All previous spectroscopic studies of An+-Ar employed resonance enhanced multiphoton ionization (REMPI) of neutral An-Ar and identified only the less stable π-bound cation due to restrictions arising from the Franck-Condon principle. The EI-IR spectrum of An+-Ar2 shows that the most stable structure of this trimer features two equivalent H-bonds (C2v symmetry). The interpretation of the experimental data is supported by quantum chemical calculations. The ab initio potential of An+-Ar calculated at the UMP2/6-311G(2df, 2pd) level features H-bound global minima ( D
e
= 513 cm-1) and π-bound local minima ( D
e
= 454 cm-1), with a barrier of V
b
≈ 140 cm-1 for isomerization from the π-bound toward the H-bound minimum.
Received 4 February 2002 Published online 13 September 2002 相似文献
13.
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
14.
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
15.
J.U. Andersen C. Gottrup K. Hansen P. Hvelplund M.O. Larsson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):189-204
Thermionic emission from hot fullerene anions, CN
-, has been measured in an electrostatic storage ring for even N values from 36 to 96. The decay is quenched by radiative cooling and hence the observations give information on the intensity
of thermal radiation from fullerenes. The experiments are analysed by comparison with a simulation which includes the quantisation
of photon energy and the statistics of emission. Experiments with heating of the molecules with a laser beam confirm the interpretation
of the observations in terms of radiative cooling and give an independent estimate of the cooling rate for C60
-. The measured cooling rates agree in general within a factor of two with the prediction from a classical dielectric model
of a thermal radiation intensity of ∼ 300 eV/s for C60 at 1 400 K, scaling approximately with the 6th power of the temperature and with the number of atoms in the molecule.
Received 12 March 2001 and Received in final form 12 June 2001 相似文献
16.
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
17.
T. Döppner Th. Diederich J. Tiggesbäumker K.-H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):13-16
Magnesium clusters grown in helium droplets and ionized with femtosecond laser pulses have been studied by high resolution
mass spectrometry. For moderate laser intensities the abundance spectra show characteristic features indicating electronic
shell effects. Compared to clusters of s1-electron metals additional shell closures appear resulting from an electron rearrangement. Irradiation with higher laser
intensities leads to a decomposition of the magnesium clusters into atomic ions. Due to charge exchange with the surrounding
helium matrix mainly singly and doubly charged magnesium ions remain. In addition, the occurrence of MgHeN
+-complexes is observed. Their abundance depends on the shape of the laser field, i.e. the laser width and the optical delay when applying the pump-probe technique.
Received 2 January 2001 相似文献
18.
P. Parneix 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):375-383
The isomerization and evaporation processes in the neutral homogeneous (CH3CN)n molecular clusters (n
= 2-7) have been investigated using classical molecular dynamics simulations. The evaporation rate constants and the kinetic energy
release in the dissociation have been analysed as a function of the cluster size and as a function of the internal energy
in the parent cluster. The competition between monomer and dimer ejections has been also carefully studied. All the dynamical
properties in these dissociative processes have been discussed in relation to the static properties of the clusters involved
in the dissociation and also in relation to the solid-liquid like transition which appears in these homogeneous molecular
clusters.
Received 19 November 2002 / Received in final form 5 February 2003 Published online 29 April 2003
RID="a"
ID="a"e-mail: pascal.parneix@ppm.u-psud.fr
RID="b"
ID="b"Laboratoire associé à l'université Paris-Sud. 相似文献
19.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
20.
A.A. Raduta E. Garrido E. Moya de Guerra 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):65-77
Some properties of small sodium clusters, comprising up to 45 atoms, are described using a projected spherical single particle
basis. The variation of the cluster shape and inner density with the number of atoms is studied. Seemingly chestnut, clusterization
and halo like structures are identified for several metallic clusters. Static polarizabilities and plasmon frequencies are
calculated and compared with experimental data and with results obtained in different approaches.
Received 28 November 2000 and Received in final form 15 February 2001 相似文献