共查询到20条相似文献,搜索用时 15 毫秒
1.
B. Vezin Ph. Dugourd D. Rayane P. Labastie J. Chevaleyre M. Broyer 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):128-130
Ionization Potentials of LinHm clusters have been measured by photoionization. As in Lin, odd-even alternations and shell closing effects are observed. In a first approximation, we find that LinH clusters behave like Lin–1 and LinH2 like Lin–2. The results may be interpreted by assuming that the bonding of one hydrogen localizes one electron and that the other electrons remain delocalized. 相似文献
2.
K. Kaya T. Sugioka T. Taguwa K. Hoshino A. Nakajima 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):201-203
Sodium doped silicon clusters (SinNam, 3n11, 1m4) were produced by two independent laser vaporization methods and their ionization potentials were measured by scanning the wavelength of the UV dye laser. The IPs of most SinNam clusters decrease monotonously with the number of Na atoms, but IPs of Si7Nam and Si10Nam clusters show an apparent even-odd alternation; odd numbers of Na atoms efficiently decrease the IP but even numbers of Na atoms never significantly decrease the IPs. In addition, the reactivity of SinNam clusters for NO molecules was investigated with a fast flow reactor, and an anti-correlation between IP and the reactivity was clearly observed; clusters having high IP show low reactivity andvice versa. 相似文献
3.
Samuel Moukouri Claudine Noguera 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):198-200
We study the size dependence of the electronic and structural properties of small MgO, CaO and NaCl clusters (up to 12 atoms), thanks to a selfconsistent tight binding approach in which we treat electrostatic and covalent effects on the same level. We discuss the conditions under which the ionic charges get reduced and the interatomic distances are contracted or dimerized. 相似文献
4.
We investigate the electronic and structural properties of small (N 20) and medium sized (N 500) clusters of Cu, using the first principles Tight-Binding Linear Muffin-Tin Orbitals (TB-LMTO) method in connection with the real-space recursion scheme. We find the electronic structure resembling the one of simple alkali metal clusters: Pronounced shell closing effects can be identified in the ionization potentials as well as in the HOMO-LUMO gaps for the magic sizesN=8, 20, 34 and 40. The low-energy equilibrium geometries show considerable Jahn-Teller distortions, just as in the case of alkali metals.This article was processed using Springer-Verlag TEX Z.Physik D macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
5.
D. G. Vlachos L. D. Schmidt R. Aris 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):156-158
Structures of small clusters of Ni, Pd, Pt, Cu, Ag, and Au with n=2–34 and n=55 atoms are calculated as functions of number of atoms and temperature by the simulated annealing Monte Carlo method using an embedded atom potential. 相似文献
6.
The electronic energy loss of a positively charged projectile passing through a sodium cluster is calculated by the semiclassical Vlasov method. The electron density before impact is obtained within the localdensity approximation in the jellium model. For the dynamical response, the Vlasov equations are solved by test particle discretization. The model gives the correct breathing mode and dipole Mie frequencies. The energy deposit is calculated as a function of projectile velocity, charge and impact parameter and is compared with theoretical and tabulated values for bulk sodium. 相似文献
7.
8.
S. Frauendorf 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,35(3):191-197
An expression for the evaporation rate of neutral atoms from a hot liquid cluster is suggested. It combines Weisskopf's statistical model with a level density that is derived from the experimentally known free energy of a macroscopic droplet of the cluster material. For the case of sodium clusters, it is compared with the rate based on the level density of a system of oscillators. For the same internal energy the latter gives substantially larger evaporation rates, whereas for equal temperature the increase is moderate. For large clusters the electronic contribution to the entropy can no longer be neglected. 相似文献
9.
Michael S. Hansen Hidetoshi Nishioka 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,28(1):73-80
Hartree-Fock calculations are done for finite number of valence electrons (8, 20, 40, and 58) in a positively charged uniform background (jellium) with the density of bulk sodium. Differences and similarities with the results of Kohn-Sham local-density calculations are discussed. State-dependence and suppression of the wave functions are the two important effects coming from the nonlocality of the Hartree-Fock potential. These two effects, however, cancel in the density profile of electrons. The Kohn-Sham calculations consequently produce similar density profiles as in the Hartree-Fock calculations. The dipole polarizability is also calculated for 8-mers. The calculated value is still smaller than the measured one and is not an improvement of the insufficient Kohn-Sham result.deceased 相似文献
10.
X. Biquard O. Sublemontier J. P. Visticot J. M. Mestdagh P. Meynadier M. A. Gaveau J. Berlande 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,30(1):45-52
The effects of adding molecules on the LIF at 540 nm of a barium atom at the surface of an argon cluster (average size 420) has been investigated. We showed that molecules like ethanol,n-hexane and O2 from stable complexes with ground state barium. In the case of molecules like N2, CH4 and SF6, the collisional quenching of solvated Ba(1
P) is observed. The large quenching rates obtained are interpreted by a surface mobility of the collisional partners. Moreover, we showed that this collisional quenching leads to the ejection of free Ba(3
P
1). 相似文献
11.
Q. Wang M. P. Iñiguez J. A. Alonso 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,31(4):299-301
Low temperature structures, melting and evaporation temperatures of A18B clusters with Lennard-Jones interactions have been studied using Molecular Dynamics simulations for different values of the parameters representing (a) the size ratio between A and B atoms, and (b) the ratio between the strengths of the A - B and A - A interactions.This paper was originally submitted in connection with the 2nd. Int. Conference on Atoic and Nuclear Clusters held in Santorini from 28. June–2. July 1993 and is published here as a regular article after an independent refereeing procedure according to the standards of Z. Phys. D 相似文献
12.
Sunil Desai C. S. Feigerle John C. Miller 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):183-185
Supersonic jet expansions of mixtures of nitric oxide with either nitrous oxide or carbon dioxide have been investigated over a wide range of relative concentrations. Mixed molecular cluster ions of the form (NO)
m
+
(N2O)n and (NO)
m
+
(CO2)n are detected following non-resonant two-photon ionization. Over a wide range of intermediate concentrations, the cluster ion distributions (NO)
3
+
(N2O)n and (NO)
3
+
(CO2)n with n30 are significantly more intense than clusters containing other numbers of nitric oxide molecules. The extra abundance of these species is attributed to their especially stable structures and several possible forms are discussed. An intriguing possibility involves a stable cyclic nitric oxide trimer (or ion) when combined with nitrous oxide or carbon dioxide clusters. 相似文献
13.
N. E. Bogdanchikova M. N. Dulin 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):48-50
Small silver clusters characterized by an absorption band (a.b.) at 320–340 nm were stabilized in matrices of different chemical nature. Among them Ag-alumosilicate was a most suitable system for cluster study by different physical and chemical methods. Clusters introduced into the zeolite of mordenite kind were found to be the most stable. Size of stabilized silver clusters measured by different methods is discussed. 相似文献
14.
Romuald Poteau Fernand Spiegelmann Pierre Labastie 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,30(1):57-68
Using a distance-dependent tight-binding hamiltonian, we have studied the influence of the temperature on the geometries of small alkali clusters (Na4, Na8, and Na20). We have applied a Monte-Carlo thermodynamical method which consists in performing canonical samplings for various temperatures, these samplings being reexpressed in the microcanonical ensemble. This method provides thermodynamical values such as the entropy and the specific heat. Their behaviour shows one phase transition in the case of Na4 and Na8, and two phase transitions for Na20. As concerns Na4 and Na8, the transition occurs at 200 K, between a solid-like phase and a phase for which the geometry of these clusters oscillates between numerous shapes. In the case of Na20, the two observed phase transitions can be described as a melting of the surface atoms (at 200 K) preliminarily to the fluctuation of an inner icosahedron seed (at 300 K). 相似文献
15.
P. Rymuza T. Ludziejewski Z. Sujkowski M. Carlen J. -Cl. Dousse M. Gasser J. Kern Ch. Rhême 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,24(1):71-79
We report a self consistent tight binding calculation of the cohesion energy of small MgO clusters, up to 12 atoms. We discuss the size variation of the charges, the bond lengths, the electronic gaps. For the first time, we predict the existence of a strong dimerization of the bond length in the small clusters. We underline the consequences of the competition between covalent and electrostatic effects in these ionocovalent systems. 相似文献
16.
J. Urban H. Sack-Kongehl K. Weiss 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,28(3):247-255
Multislice calculations have been performed for Ag, Pd and Au clusters in the size range of 5.0 nm diameter of cuboctahedral, icosahedral and decahedral structures. It could be shown that tilt series are necessary for the classification of the structures. Particularly for arbitrary orientations, i.e. deviations from main directions such as 2-, 3- and 5-fold axes, the performance of computer simulations is mandatory. The influence of absorption is also studied for the case of a 100 kV microscope by introducing a complex potential. 相似文献
17.
B. Montag P. -G. Reinhard 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,33(4):265-279
The ground-state structure and shape parameters of neutral and singly charged simple metal clusters with up to 40 valence electrons have been calculated within the cylindrically averaged pesudopotential scheme (CAPS). Na and Ba have been chosen as typical monovalent and divalent metals. The obtained structures agree very well with the results of more elaborate methods. A simple growth pattern for the most stable ionic geometries is deduced. The ionic and electronic multipole moments from CAPS are very similar to those of the structure averaged jellium model (SAJM) and of the plasma model. The surface energies derived from the CAPS results agree with experimental values. 相似文献
18.
Alexander Goerke Gregor Leipelt Hartmut Palm C. P. Schulz I. V. Hertel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,32(4):311-320
The first reactive differential scattering study for atomic clusters is reported. Oxidation of Na
x
(x8) with O2 is investigated in a crossed beam apparatus. Sodium oxide (Na
n
O,n4) and sodium dioxide (Na
n
O2,n6) are produced with a total reactive cross section from 50 to 80 Å2, depending on the cluster size. The excess energies for these reactions are estimated by an SCF type ab initio calculation and range from 0.5 to 5 eV. The large cross section may then be understood quantitatively in terms of a harpooning mechanism as a first step in the reaction path. Angular distributions have been determined for the most abundant products, showing strong forward scattering. Two different schemes are discussed for the reaction: while the dioxides Na
n
O2 may be formed by an evaporative cooling process from a highly excited collision complex, formation of Na
n
O appears to originate from a direct process. In both cases the experimental data suggest that most of the exothermicity remains in the reaction products. 相似文献
19.
N. Watanabe H. Shiromaru Y. Negishi Y. Achiba N. Kobayashi Y. Kaneko 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):252-254
Reactions of carbon clusterions with O2 were studied by using an RF ion trap in which cluster ions of specific size produced by laser ablation could be stored selectively. Reaction rate constants for positive and negative carbon cluster ions were estimated. In the case of the positive cluster ions, these were consistent with the previous experimental results using FTMS. Negative carbon cluster ions C
n
–
(n=4–8) were much less reactive than positive cluster ions. The CnO– products were seen only in n=4 and 6. 相似文献
20.
K. Athanassenas T. Leisner U. Frenzel D. Kreisle E. Recknagel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):153-155
Photoexcitation and photoionization experiments on small Tungsten and Niobium clusters were performed with a Q-switched Nd:YAG laser (1064 nm) and a reflectron type time-of-flight mass spectrometer. For low laser fluences the monomer and very small clusters do not show up in the mass spectra. Furthermore, the detected cluster ions show very asymmetric peak shapes caused by delayed ionization (thermionic emission). For high photon fluences photoions with up to charge state +3 could be detected. 相似文献