共查询到20条相似文献,搜索用时 46 毫秒
1.
J.M. Mestdagh M. Berdah N. Auby C. Dedonder-Lardeux C. Jouvet S. Martrenchard-Barra D. Solgadi J.P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):291-302
The photodissociation of a chlorine molecule in the environment of a xenon cluster has been studied experimentally using the
real time pump and probe technique through the formation of an XeCl reaction product. The photodissociating system is probed
in such a way that the movement of a single chlorine atom in the xenon environment is detected. Various XenCl2 cluster sizes have been investigated leading to the distinction between uncapped, half-capped and doubly capped structures
for these clusters. These structures have a profound influence on the photodissociation dynamics. Retrapping of one chlorine
atomic fragment and stabilization of the XeCl reaction product is only observed for the half and doubly capped clusters. The
experimental work is complemented by classical molecular dynamics calculations to get a full picture of the photodissociation.
Received: 17 February 1998 / Received in final form and Accepted: 28 July 1998 相似文献
2.
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
3.
R. Guirado-López D. Spanjaard M.-C. Desjonquères 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):459-466
The magnetic properties of small YN clusters are studied by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. Several
types of cluster geometries are considered in order to see the effects of the size and symmetry of the structures on the magnetic
properties. The average magnetic moments are found to be constant over large domains of variations in the interatomic distance, a fact that can be explained by the
existing closed shell electronic configurations at least for one spin direction in all our magnetic solutions. Small energy
gains upon the onset of magnetization are obtained, which reveals the low stability of the magnetic solutions. Our results
contradict the prediction of a magnetic-nonmagnetic transition at a large cluster size (about 90 atoms) for these kinds of
systems.
Received: 27 April 1998 / Received in final form: 23 June 1998 / Accepted: 17 July 1998 相似文献
4.
R. Thissen P. Lablanquie R.I. Hall M. Ukai K. Ito 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):335-342
Photoionization of rare gas clusters in the innervalence shell region has been investigated using threshold photoelectron
and photoion spectrometers and synchrotron radiation. Two classes of states are found to play an important role: (A) valence
states, correlated to dissociation limits involving an ion with a hole in its innervalence ns shell, (B) Rydberg states correlated to dissociation limits involving an ion with a hole in its outervalence np shell plus an excited neutral atom. In dimers, class A states are “bright”, that is, accessible by photoionization, and serve
as an entrance step to form the class B “dark” states; this character fades as the size of the cluster increases. In the dimer,
the “Mulliken” valence state is found to present a shallow potential well housing a few vibrational levels; it is predissociated by the
class B Rydberg states. During the predissociation a remarkable energy transfer process is observed from the excited ion that
loses its innershell electron to its neutral partner.
Received: 10 February 1998 / Revised: 17 July 1998 / Accepted: 31 July 1998 相似文献
5.
M. Sassetti B. Kramer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):357-367
The Raman spectra of quantum wires in the region of electronic intra-band excitations are investigated using one- and two-band
models based on the Luttinger approximation with spin. Structures related to charge and spin density modes are identified,
and analyzed with respect to their behavior with photon energy and temperature. It is found that the low-energy peaks in the
polarized spectra, close to resonance that are commonly assigned to “single particle excitations”, can be interpreted as the
signature of spin density excitations. A broad structure in the resonant depolarized spectrum is predicted above the frequency
of the spin density excitations. This is due to simultaneous but independent propagation of spin and charge density modes.
The results, when compared with experiment, show, that the electronic collective excitations of quantum wires at low energies
are characteristic for a non-Fermi liquid.
Received: 25 March 1998 / Accepted: 3 June 1998 相似文献
6.
K. Hashimoto M. Okamoto K. Takayanagi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):75-78
The stability of neutral, singly and multiply ionized silicon clusters, (N
= 2-7, M
= 0, , , ), has been investigated using an ab initio density functional method. We show that the fragmentation effect significantly affects the structure of mass-spectra of multiply
ionized silicon clusters. For clusters, the clusters with a large fragmentation energy are found to correspond to the high peaks at N = 4 and 6 in mass-spectra. For clusters, a peak at N = 5 in mass-spectra has been predicted to be especially high.
Received: 9 June 1997 / Revised: 8 January 1998 / Accepted: 25 February 1998 相似文献
7.
W. Kleinig V.O. Nesterenko P.-G. Reinhard Ll. Serra 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):343-352
The systematics of the plasmon response in spherical K, Na and Li clusters in a wide size region is studied. Two simplifying approximations whose validity has been established previously are considered: (a) a separable
approach to the random-phase-approximation, involving an expansion of the residual interaction into a sum of separable terms,
(b) the electron-ion interaction is modeled within the pseudo-Hamiltonian jellium model (PHJM) including nonlocal effects
by means of realistic atomic pseudoHamiltonians. In cases where nonlocal effects turn out to be negligible, the Structure
Averaged Jellium Model (SAJM) has been used. The leading role of Landau damping in forming the plasmon width in medium and
large clusters is demonstrated. Good agreement with available experimental data is achieved for K, Na (using the SAJM) and
small Li clusters (invoking the PHJM). The trends for peak position and width are generally well reproduced, even up to details
of the Landau fragmentation in several clusters. Less good agreement, however, is found for large Li clusters. The possible
reasons of the discrepancy are discussed.
Received: 22 April 1998 / Accepted: 24 July 1998 相似文献
8.
L. Dukan L. del Fabbro P. Pradel O. Sublemontier J.M. Mestdagh J.P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):257-265
Photofragmentation of Fe(H2O)n
+
clusters (n
=1-9) is investigated at three different wavelengths, 532, 355 and 266 nm. Two fragmentation pathways are observed depending essentially
on the photon energy, but also on the parent size n. The fragmentation products belong to two ion families, Fe(H2O)m
+
and FeOH(H2O)m
+
, which correspond to dehydration and intracluster dehydrogenation reactions respectively. The ion yields are studied as a
function of the laser fluence in order to determine the number of photons implied in the photofragmentation process. This
allows us to estimate that the D[(H2O)n-1Fe+-(H2O)] bond energy is ranging between 0.44 eV and 0.55 eV for .Photon absorption cross sections are also derived from the fluence experiments, and two different behaviors are observed:
i) At 355 nm, far away from any transition, progressive solvation of the metal ion results in an increasing absorption cross section from n
=2 to n
=9. This can be attributed to a forbidden transition of bare , which becomes progressively allowed because of the interaction with more and more water ligands. ii) At 266 nm, close to
several allowed transitions of bare , a distinct maximum is observed for the absorption of ion. It may be attributed to a change in the spin multiplicity when switching from and on one hand to Fe(H2O) on the other.
Received: 11 November 1997 / Revised: 18 February 1998 / Accepted: 22 April 1998 相似文献
9.
M.L. Gardel R. Vandenbosch B.P. Henry C. Cooper D.I. Will 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):79-81
The destruction cross-section for 22.5 and 50 keV C1- , for 10 and 50 keV C8
1- and for 50 and 75 keV C60
1- clusters in collisions with H2 has been measured by an attenuation method. The destruction of the cluster anions is dominated by electron detachment rather
than fragmentation and is of the order of the geometric cross-section. The cross-sections vary little with bombarding energy.
Received: 16 September 1998 / Received in final form: 23 February 1999 相似文献
10.
M. Bertolus V. Brenner P. Millié 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(2):197-205
A theoretical study of clusters with using density functional theory is presented. Tests of various functionals demonstrate that local spin density approximation
(LSDA) is the most adequate functional for the study of these systems. Structures, vibrational frequencies, and IR intensities
of the lowest energy isomer of the studied clusters obtained using LSDA are described, and the unusual properties of the Si-C
clusters are discussed. A quantitative analysis of the obtained structures was carried out, and relations between the coordinations,
interatomic distances, and angles observed in the Si-C clusters were obtained through introduction of the notion of coordination.
This analysis also shows that the carbon atoms mainly exhibit sp and sp2 hybridizations, and that a majority of silicon atoms do not hybridize. This study is the fi
rst step of the implementation of a semi-empirical potential, which would describe the moderately small Si-C clusters.
Received: 20 October 1997 / Received in final form: 16 December 1997 / Accepted: 17 December 1997 相似文献
11.
12.
R. Guirado-López D. Spanjaard M.-C. Desjonquères A.M. Oleś 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):437-446
We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (Oh) and icosahedral (Ih) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence
of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of
Oh and Ih clusters as a function of the atomic number along the 4
d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior
as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations.
Received: 20 November 1997 / Received in final form: 9 March 1998 / Accepted: 30 March 1998 相似文献
13.
14.
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
15.
A. Domps E. Suraud P.-G. Reinhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(3):191-194
By comparing quantal and semi-classical calculations of optical response, we work out the part of the splitting of the plasmon
spectra which is exclusively due to geometrical effects. We apply the analysis to the test case which exhibits an interesting geometry with strong prolate quadrupole deformation and a pronounced asymmetry in addition.
We find a new type of resonance splitting which is due to geometrical effects but goes beyond the simple and well known deformation
splitting.
Received: 6 April 1998 / Accepted: 24 April 1998 相似文献
16.
G. Mattei F. Toigo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):245-256
The effect of non-local norm-conserving pseudo-potentials on the static and dynamic properties of Nan and Lin cluster with n=6,8 is investigated in the frame of self-consistent LDA calculations with spherically averaged ionic density (SAPS model).
A comparison with previous calculations which use local pseudo-potentials as well with uniform averaged non-local pseudo-jellium
calculation has been carried out. A better quantitative agreement with experiments has been found in the calculation of the
photoresponse cross-section with respect to either simple jellium or pseudo-jellium model, even in very small clusters, where
deviations from sphericity are not negligible.
Received: 3 March 1998 / Received in final form and Accepted: 2 June 1998 相似文献
17.
I. L. Garzón M. R. Beltrán G. González I. Guterrez-González K. Michaelian J. A. Reyes-Nava J. I. Rodrguez-Hernández 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):105-109
Theoretical and experimental information on the shape and
morphology of bare and passivated gold clusters is fundamental
to predict and understand their electronic, optical, and other
physical and chemical properties. An effective theoretical
approach to determine the lowest-energy configuration (global
minimum) and the structures of low energy isomers (local minima)
of clusters is to combine genetic algorithms and many-body
potentials (to perform global structural optimizations), and
first-principles density functional theory (to confirm the
stability and energy ordering of the local minima). The main
trend emerging from structural optimizations of bare Au clusters
in the size range of 12-212 atoms indicates that many
topologically interesting low-symmetry, disordered structures
exist with energy near or below the lowest-energy ordered
isomer. For example, chiral structures have been obtained as the
lowest-energy isomers of bare Au28 and
Au55 clusters, whereas in the size-range
of 75-212 atoms, defective Marks decahedral structures are
nearly degenerate in energy with the ordered symmetrical
isomers. For methylthiol-passivated gold nanoclusters
[Au28(SCH3)16
and
Au38(SCH3)24],
density functional structural relaxations have shown that the
ligands are not only playing the role of passivating molecules,
but their effect is strong enough to distort the metal cluster
structure. In this work, a theoretical approach to characterize
and quantify chirality in clusters, based on the Hausdorff
chirality measure, is described. After calculating the index of
chirality in bare and passivated gold clusters, it is found that
the thiol monolayer induces or increases the degree of chirality
of the metallic core. We also report simulated high-resolution
transmission electron microscopy (HRTEM) images which show that
defects in decahedral gold nanoclusters, with size between 1-2
nm, can be detected using currently available experimental HRTEM
techniques. 相似文献
18.
G.M. Koretsky M.B. Knickelbein 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(3):273-278
The photoionization spectra of Pr2-Pr21 and Ce2-Ce17 have been measured near threshold. The ionization potentials (IPs) of and vary discontinuously with size, but trend downward toward the work function of the bulk metals. In general, the IPs of cerium
clusters display more variation than those of praseodymium clusters. The sudden discontinuities observed in the IPs of both
and is akin to that displayed by clusters of transition metal atoms, suggesting that as in transition metal clusters, the rapid
evolution in geometric structure with size is the source of these discontinuities.
Received: 2 January 1998 / Accepted: 10 March 1998 相似文献
19.
F. Despa W. Bouwen F. Vanhoutte P. Lievens R.E. Silverans 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):403-411
The influence of doping of Li-clusters by electronegative O and C atoms on the ionization potentials was investigated. Experimentally,
we report ionization potentials for bare Lin clusters deduced from photoionization efficiency spectra. The values are compared with the results for LinO and LinC clusters. Observed differences are largely attributed to a quantum size effect caused by the segregated molecular part around
the impurity, which changes the electron work function. Theoretically, the Fermi and exchange-correlation energies which enter
the work function, are calculated in the frame of the augmented plane wave (APW) method by taking explicitly into account
the presence of the molecular core. The other contribution to the work function, the moment of the double layer at the cluster
surface, is computed by solving the corresponding Poisson's equation.
Received 9 September 1999 and Received in final form 7 February 2000 相似文献
20.
S. Martin J. Bernard L. Chen A. Denis J. Désesquelles 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):1-6
Electron capture by Ar8+ in collisions with C60 fullerene has been investigated using coincident measurements of the number n of ejected electrons, the mass and charge of multicharged Cr+
60
recoil ions and their fragments Ci+
m and the final charge state of outgoing projectiles Ar(8-s)+ (). The number of captured electrons r is the sum of the numbers of stabilized and emitted electrons: r
=
n
+
s. The ratio n
/
s decreases by a factor three with s increasing from 1 to 7 showing that the multiply excited states populated by capture of a large number of electrons are rather
stable against auto-ionisation. Each kinetic energy spectrum of Ar+ and Ar2+ projectiles is composed of two peaks which we attribute to collisions “inside” and “outside” the C60 cage. The measured energy shift of the projectile keV is consistent with the corresponding energy loss keV in a carbon foil with an equivalent thickness. Inside collisions are characterized by a strong dissociation of recoil
ions into light monocharged fragments and by a high multiplicity of ejected electrons.
Received: 25 March 1998 / Received in final form and Accepted: 9 June 1998 相似文献