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2.
The structure and stability of small neutral and positively charged zinc oxide (ZnO)
n
clusters (n = 2−9) have been studied within the density functional theory. For n ≤ 7, the most stable clusters are shown to be flat rings; for n = 8, 9, the clusters are mainly three-dimensional cage structures. The energies and main channels of fragmentation of the
clusters have been determined. It has been found that the fragmentation of the charged clusters with n > 6 occurs predominantly with formation of a (ZnO)4+ ion, which explains the available mass spectrometric data on ionization of the zinc oxide clusters by electron impact. 相似文献
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4.
G. Martinet M. Chabot K. Wohrer S. Della Negra D. Gardès J. A. Scarpaci P. Désesquelles V. Lima S. Díaz-Tendero M. Alcamí P.-A. Hervieux M. F. Politis J. Hanssen F. Martín 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):149-152
We report on experimental and theoretical efforts designed
to understand the fragmentation of small carbon clusters.
Experimentally, a new detection system for high velocity
fragments has been recently developed allowing the fragmentation
of high velocity clusters to be totally recorded [1]. Results
for the branching ratios of deexcitation of
C5 and C9 formed
by electron capture in high velocity
collisions are presented. Theoretically, the dissociation
dynamics of C5 has been investigated
using a kinematical model based on the statistical theory of
Weisskopf. In this model various structural quantities
(geometries, dissociation energies, harmonic frequencies), are
required for both the parent cluster and the fragments. They
have been calculated within DFT and coupled-cluster formalisms
for Cn up to n = 9.
In all cases, a strong correlation between measured branching
ratios and calculated dissociation energies is observed. 相似文献
5.
C. M. Chaves A. Troper 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(1):37-40
In this work we discuss the occurrence of ferromagnetism in transition-like metals. The metal is represented by two hybridized
(V) and shifted (epsilons) bands one of which includes Hubbard correlation whereas the other is uncorrelated. The starting point is to transform the
original Hamiltonian into an effective one. Only one site retains the full correlation (U) while in the others the correlations
are represented by an effective field, the self-energy (single-site approximation). This field is self-consistently determined
by imposing the translational invariance of the problem. Thereby one gets an exchange split quasi-particle density of states
and then an electron-spin polarization for some values of the parameters (U,V, α, epsilons), α being the ratio of the effective masses of the two bands and of the occupation number n. 相似文献
6.
A. A. Valuev A. S. Kaklyugin G. É. Norman 《Journal of Experimental and Theoretical Physics》1998,86(3):480-488
This paper shows how the concepts commonly used for a Debye plasma—Landau damping, collisional damping, short-range and long-range
collisions, and plasma waves—must be revised to describe a nonideal electron-ion plasma. The degrees of freedom of a nonideal
plasma are divided into collective and individual. The increase and saturation of the fraction of collective degrees of freedom
as the coupling constant increases is discussed. The Tatarskii approach for a system of coupled oscillators makes it possible
to model the collective degrees of freedom of a nonideal plasma by a set of Langevin oscillators in a thermostat. The correlation
energy and the energy of the plasma waves are found. The concepts developed here made it possible to determine the dispersion
of the plasma waves and their damping. The effect of damping on the discrepancy between the position of the maximum of the
dynamic structure factor and the real part of the solution of the dispersion equation is considered. The effective collision
frequency of the individual degrees of freedom (the electrons) is estimated, taking into account both short-range pairwise
scattering and scattering at plasma waves.
Zh. éksp. Teor. Fiz. 113, 880–896 (March 1998) 相似文献
7.
The relaxation processes (α, β, and γ) in UHMW PE fibres drawn to different draw ratios λ have been studied by dynamic-mechanical and nuclear magnetic resonance methods. The temperature dependences of tensile loss
moduli E″ and spin-lattice relaxation times T
1 have been analyzed assuming distribution of correlation times τ according to the Davidson—Cole function. The activation energies E
a and parameters ε characterizing widths of distribution, and asymptotic value τ
0 for correlation times have been determined from experimental data for low-temperature γ-process and for high-temperature α-process. A weak β-process has been found by dynamic-mechanical method and quantitative analysis was made only for fibres with λ = 9. The temperature dependences of second moment M
2 of the broad-line NMR spectra have been analyzed according to the Gutowsky—Pake formula, which includes only a single correlation
time τ
c without distribution. In this case the activation energies E
a and values of τ
0 have been determined. 相似文献
8.
Cross sections for ionization and ionic fragmentation of pyrimidine molecules by electron collisions
I. Linert M. Dampc B. Mielewska M. Zubek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(1):20
The electron impact mass spectroscopy and the total ion collection measurements were used
to investigate the ionization and ionic fragmentation of the pyrimidine,
C4H4N2, molecules in the gas phase. The cation mass
spectra were measured in the 10−85 amu range and the observed mass peaks assigned to
corresponding ionic fragments. The most abundant cation in the mass spectra is the parent
cation, C4H4N
\hbox{2+_{\mathrm{2}}^{\mathrm{+}}}
+
2
,
at 80 amu. The appearance energies of the ionic fragments were determined and the possible
fragmentation processes are discussed. The electron impact absolute total and partial
ionization cross sections in pyrimidine were obtained over the energy range from the
respective ionization thresholds up to 150 eV. 相似文献
9.
The pulsed optoacoustic method is studied to measure absolute infrared multiphoton absorption cross sections. The influence
of the thermalisation by the walls of the cell is shown to be very important at low pressure. This influence is analysed both
experimentally and theoretically by solving the coupled diffusion and relaxation equations for vibrational and translational
energies. The sensitivity of the method is limited by a spurious pressure signal present even with non-absorbing gases. This
parasitic signal is attributed to an absorption located on the inner surface of the windows of the cell. For instance, using
KCl windows, the observed spurious signal corresponds to about 10−4 of the total laser energy, transmitted from the windows to the gas. This proportion is independent on the energy fluence.
Taking care of these limitations, we have measured the absorption cross section of CF3I at the different wavelengths of the (001–020) transitions of the CO2 laser. The typical energy fluences in these experiments were varied from 10−3 to 1J/cm2. To be in collision free conditions, the CF3I pressure was made equal to 0.2 Torr. 相似文献
10.
X. Liang Y.-H. Luo X.-J. Feng T. T. Cao L. X. Zhao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):93-101
The structures, binding energies, and electronic properties of
Cn and NaCn (n=2–12) clusters have been systematically
investigated using density functional theory (DFT). A number of
previously undiscovered isomers of NaCn clusters are reported,
including fan-like, linear and three-dimensional structures.
Moreover, NaCn clusters with even n are found to be more
stable than those with odd n, in contrast with
the case of Cn clusters. 相似文献
11.
12.
P. Pradhan A. K. Ray 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,37(3):393-407
The theoretical formalism of local density approximation (LDA) to density
functional theory (DFT) has been used to study the electronic and geometric
structures of SimCn+ (1≤m, n ≤4)
cationic clusters. An all electron 6-311++G** basis set has been used and
complete geometry optimizations of different possible structures for a
specific cluster have been carried out. Binding energies, relative energies,
fragmentation energies, vibrational frequencies, and adiabatic ionization
potentials of the optimized clusters have been investigated and reported in
detail. Results have been compared with other experimental and theoretical
results available in the literature. 相似文献
13.
Equilibrium geometries, charge distributions, stabilities and electronic properties of the Ag-adsorbed (MgO)
n
(n = 1–8) clusters have been investigated by density functional theory (DFT) with generalized gradient approximation (GGA) for
exchange-correlation functional. The results show that hollow site is energetically preferred for n⩾4, and the incoming Ag atoms tend to cluster on the existing Ag cluster. The Mulliken populations indicate that the interaction
between the Ag atom and Magnesia clusters is mainly induced by a weak atomic polarization. The adsorbed Ag atom only causes
charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural
features of Magnesia clusters is minor. Furthermore, the investigations on the first energy difference, fragmentation energies
and electron affinities show that the Ag(MgO)4 and Ag(MgO)6 are the most stable among studied clusters.
Supported by the Startup Fund of High-level Personal for Shihezi University (Grant No. RCZX200747) 相似文献
14.
U. Busolt E. Cottancin H. Röhr L. Socaciu T. Leisner L. Wöste 《Applied physics. B, Lasers and optics》1999,68(3):453-457
n
+ clusters (n=2-9)deposited onto highly oriented pyrolytic graphite (HOPG) substrates at liquid nitrogen temperatures. The
deposition was carried out with variable kinetic energies of the clusters. Clusters deposited with high kinetic energy (up
to 60 eV/cluster) become fragmented upon impact. For low deposition energies (1–4 eV/cluster) the size dependence of the photoelectron
spectra reveals a pronounced odd/even effect, which is well known for gas phase silver clusters. This indicates that the soft
deposited clusters retain their size and identity on the sample. The phase of the odd/even effect suggests that transient
negatively charged cluster ions serve as an intermediate step in the two-photon photoemission process. The lifetime of the
anions rises with cluster size. This is attributed to an increasing electronic density of states for larger clusters.
Received: 26 October 1998 / Revised version: 16 December 1998 相似文献
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16.
A. Bartecka A. Bacławski T. Wujec J. Musielok 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,37(2):163-169
Experimental Stark-broadening studies of two selected
doubly excited NI multiplets from the infrared wavelength range are
presented. One of them is very sensitive to interactions with
charged particles in plasmas and the other exhibits — at the same
plasma conditions — only very small broadening and shift. A high
current wall-stabilized arc operated in helium with admixture of
nitrogen and hydrogen was applied as the excitation source. The
radiation of the plasma was detected by applying a grating
spectrometer equipped with a CCD detector. Measurements were
performed at electron densities of the plasma between
3×1015 and 7×1015 cm-3, corresponding to
temperatures from the range 8000–10500 K. Electron impact widths
(we) and shifts (de) of fine structure components of these
multiplets were determined. The evaluated Stark broadening
parameters (we, de) are compared with other experimental
data and with calculated Stark effect constants. 相似文献
17.
In this paper we study random partitions of {1,…,n} where every cluster of size j can be in any of w
j
possible internal states. The Gibbs (n,k,w) distribution is obtained by sampling uniformly among such partitions with k clusters. We provide conditions on the weight sequence w allowing construction of a partition valued random process where at step k the state has the Gibbs (n,k,w) distribution, so the partition is subject to irreversible fragmentation as time evolves. For a particular one-parameter
family of weight sequences w
j
, the time-reversed process is the discrete Marcus–Lushnikov coalescent process with affine collision rate K
i,j
= a+b(i+j) for some real numbers a and b. Under further restrictions on a and b, the fragmentation process can be realized by conditioning a Galton–Watson tree with suitable offspring distribution to have
n nodes, and cutting the edges of this tree by random sampling of edges without replacement, to partition the tree into a collection
of subtrees. Suitable offspring distributions include the binomial, negative binomial and Poisson distributions.
Research supported in part by N.S.F. Grant DMS-0405779. 相似文献
18.
We have studied the dynamics of intramolecular vibrational redistribution (IVR) from the initially excited mode v1 ≈ 3330 cm−1 (acetylene-type H-C bond) in H-C≡C-CF3 molecules in the gaseous phase by means of anti-Stokes spontaneous Raman scattering. The time constant of this process is
estimated as 2.3 ns—this is the slowest IVR time reported so far for the room-temperature gases. It is suggested that so long
IVR time with respect to the other propyne derivatives can be explained by a larger defect, in this case, of the Fermi resonance
of v1 with v2 + 2v7—the most probable doorway state leading to IVR from v1 to the bath of all vibrational-rotational states with the close energies. In addition, it is shown that the observed dynamics
is in agreement with a theoretical model assuming strong vibrational-rotational mixing. 相似文献
19.
D S Narayan 《Pramana》1979,12(4):391-395
The production of prompt neutrinos in the beam dump experiment is explained in a cluster model, by postulating the emission
of strange clusters in hadron collisions, besides the usual non-strange clusters. The low mass strange clusters can decay
only by the weak interaction. The leptonic and semi-leptonic decay modes of these clusters give rise to prompt neutrinos.
A prediction of the model is that the ratios <v
e>/π
+ at PS energies would be the same as SPS energies. 相似文献
20.
Several previously unknown resonances of the μtμ helium hydride ion have been identified using a variational procedure. It
is suggested that these resonances may form in αμ(1s)-TD(T2) scattering, for centre of mass collision energies in the range 8–10 keV. If the molecular complex [(αtμ)*dee]* is formed in a dissociative state (with respect to the α tμ-d coordinate), the dissociation energy may in part be transferred to the muonic degrees of freedom, opening the exit channel
[(αtμ)*dee]* → tμ + α e + T, effectively amounting to muon transfer from α to t. We present a theoretical formulation of this novel and hypothetical mechanism for muon reactivation together with a numerical
calculation of its cross-section for a special case.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献