共查询到20条相似文献,搜索用时 15 毫秒
1.
A. E. Zarvin N. G. Korobeishchikov V. V. Kalyada V. Zh. Madirbaev 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):101-110
An experimental study of the formation of mixed van der Waals oxygen-isoprene complexes, generated in an expanding supersonic
helium-oxygen-isoprene jet at various stagnation pressures and at diverse oxygen and isoprene concentrations, has been performed.
To measure the composition and distribution of the partial densities of the individual components, molecular beam mass spectrometry
was adapted to pulsed modes of gas source operation. The particularities of applying mass spectrometry to studying clustered
isoprene streams in a pulsed mode have been discussed. The composition of small clusters generated in a free supersonic jet
has been checked for dependencies upon the initial mixture composition and stagnation pressure. The mechanism of nucleation
has been identified for different partial concentrations of impurities in the helium stream. It has been shown that, even
at a 0.3% concentration of isoprene in the mixture, nucleation starts with the formation of hydrocarbon complexes. The specific
features of the dissociative ionization of van der Waals complexes, consisting of pure isoprene and mixed complexes, have
been discussed. The conditions needed for the formation of binary oxygen-isoprene van der Waals complexes have been identified. 相似文献
2.
Structural and electronic properties of Ren (${\sf n} \leq$ 8) clusters
by density-functional theory
X. J. Feng T. T. Cao L. X. Zhao Y. M. Lei Y. Luo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,50(3):285-288
The structures, stabilities and electronic properties of
small-sized Ren (n ≤ 8) clusters have been
systematically investigated by density-functional theory. The
lowest-energy structures of Ren clusters favor 3-dimensional
configuration. The results of second-order
difference of energies indicate that Re4 and Re6 possess
relatively higher stability in structure. Importantly, our
theoretical results of electron affinity are in agreement with
experimental values, which can be responsible for the reliability
of the structures. 相似文献
3.
B. N. Onwuagba 《Il Nuovo Cimento D》1991,13(4):415-421
The ionization potentials in alkali metal clusters are calculated using a jellium-background model for positive-ion cores
and the local-spin-density functional approximation for valence electrons. The computed results compare reasonably with previous
experimental and theoretical values in the cases of Li, Na, K and Cs. 相似文献
4.
P. Feiden J. Stehlé J. Leygnier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,50(1):53-60
Nano-droplet growth in a supersaturated vapor has been investigated in a gas aggregation source using laser-ionization time-of-flight
mass spectrometry. During its propagation into an atomic vapor, a small particle grows by sticking atoms on its surface. This
accretion process has been highlighted through the clustering of homogeneous particles Mn and heterogeneous Mn(M2O) and Mn(MOH)2 particles in a metallic vapor and a helium buffer gas (M = Na or K). A modelization is introduced so as to connect the measured
cluster mass distributions to the pertinent physical parameters. The mass distribution width is particularly sensitive to
the efficiency of the first steps in the growth sequence. We used this property to compare the ability of this vapor-condensed
matter phase transition to occur around various homogeneous and heterogeneous nucleation seeds. 相似文献
5.
C. Di Paola E. Bodo F. A. Gianturco 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(3):377-385
Calculations of the quantum structures describing the initial
solvation shells of bosonic helium atoms around a polar, ionic
system like LiH+ are reported, together with the corresponding
quantum energies. The calculations were carried out using the
Diffusion Monte Carlo (DMC) approach and parametric trial functions.
Its final radial and angular distributions for clusters of varying
size are analysed and discussed. The solvation of this ionic dopant
is shown to occur in a way which is strongly affected by the
orientational induction forces between the latter molecule and the
solvent atoms, indicating the onset of “snowball" structures
at the location of the dopant and the clear distinction
between “heliophilic" and “heliophobic" regions of microsolvation. 相似文献
6.
7.
J. L. Deng K. H. Su X. Wang Q. F. Zeng L. F. Cheng Y. D. Xu L. T. Zhang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):21-35
The most stable structures of gaseous Si
m
C
n
(3 ⩽ n+m ⩽ 6) clusters in their ground electronic states are determined with the high level electronic correlation method QCISD(T)/g3large.
Thermodynamic properties on heat capacity (C
p,m
Θ), entropy (S
m
Θ), Gibbs energy function (−[G
Θ −H
Θ(T
r
)]/T) and enthalpy function (H
Θ−H
Θ(T
r
)) are predicted with standard statistical thermodynamics using the structure parameters and vibrational frequencies obtained
with B3PW91/6-31G(d) method combined with the electronic excitation energies determined with time dependent density functional (TD DFT) method
at B3PW91/6-31G(d) level. The electronic energies are calculated with the accurate model chemistry method at G3(QCI) level of theory and the
Δ
f
H
m
Θ (0 K), Δ
f
H
m
Θ (298.15 K) and Δ
f
G
m
Θ (298.15 K) values are predicted. The heat capacities C
p,m
Θ(T) as a function of temperature within 298.15-2000 K are fitted into analytical equations. The thermodynamic functions at higher
temperatures are determined classically by using these equations. Most of the results obtained in this work are consistent
with the available experiments. 相似文献
8.
Y. Liu Z-Y. Sun L-J. An 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):481-484
Banded spherulite patterns are simulated in two dimensions by means of a
coupled logistic map lattice model. Both target pattern and spiral pattern
which have been proved to be existent experimentally in banded spherulite
are obtained by choosing suitable parameters in the model. The simulation
results also indicate that the band spacing is decreased with the increase
of parameter μ in the logistic map and increased with the increase of
the coupling parameter ε, which is quite similar to the results
in some experiments. Moreover, the relationship between the parameters and
the corresponding patterns is obtained, and the target patterns and spiral
patterns are distinguished for a given group of initial values, which may
guide the study of banded spherulite. 相似文献
9.
J. Ma Z. H. Hou H. W. Xin 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(1):101-107
We study the effect of recycled noise, generated by the superposition of a
primary Gaussian noise source with a second component of constant delay, in
a parameter region below the threshold of supercritical Hopf bifurcation, by
focussing on the performance of noise induced oscillations and coherence
resonance. For fixed noise intensity, the amplitude and signal-to-noise
ratio of the oscillation show periodic dependences on the delay time. The
optimal noise intensity for the occurrence of coherence resonance also shows
a periodic dependence on the delay. A theoretical analysis based on the
stochastic normal form theory is presented, which qualitatively reproduces
the simulation results with good agreement. This work presents a possible
strategy for controlling noise induced oscillations and coherence resonance
by deliberately adjusting the parameters of the recycled noise. 相似文献
10.
E. Fort F. Pradère A. De Martino H. Vach M. Châtelet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):79-84
We present two complementary techniques that provide detailed diagnostics of supersonic beams involving several species. First,
surface scattering, together with quadrupole mass spectrometer detection, yields the monomer percentage for each species within
the beam. Second, analyses of beam profiles for different masses after scattering by a buffer gas permit determination of
mixed cluster presence and, if any, of cluster sizes and compositions. The two techniques are applied to supersonic expansions
of an argon-nitrogen mixture. We discuss the results that provide new insight in binary nucleation processes.
Received: 6 October 1997 / Revised: 4 November 1997 / Accepted: 13 November 1997 相似文献
11.
J. P. Salas 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):95-102
In this paper, we present the study of the global classical dynamics of a rigid diatomic molecule in the presence of combined
electrostatic and nonresonant polarized laser fields. In particular, we focus on the collinear field case, which is an integrable
system because the z-component Pφ of the angular momentum is conserved. The study involves the complete analysis of the stability of the equilibrium points,
their bifurcations and the evolution of the phase flow as a function of the field strengths and Pφ. Finally, the influence of the bifurcations on the orientation of the quantum states is studied. 相似文献
12.
T. Carletti D. Fanelli A. Guarino F. Bagnoli A. Guazzini 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):285-292
We here discuss the process of opinion formation in an open community where agents are made to interact and consequently update
their beliefs. New actors (birth) are assumed to replace individuals that abandon the community (deaths). This dynamics is
simulated in the framework of a simplified model that accounts for mutual affinity between agents. A rich phenomenology is
presented and discussed with reference to the original (closed group) setting. Numerical findings are supported by analytical
calculations. 相似文献
13.
M. Eryürek M. H. Güven 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(2):221-228
The solid-liquid phase transitions of Lennard-Jones clusters LJN
(N=39–55) were simulated by a microcanonical molecular dynamics method using
Lennard-Jones potential, and their thermodynamic quantities were calculated.
The caloric curves of clusters (except N=42) have S-bend. To understand this
behaviour, configurational and total entropies were evaluated, and dents on
the entropy curves were taken as a sign of negative heat capacity. The heat
capacities were evaluated for N=39–55 clusters using configurational entropy
data. The potential energy distributions have bimodal behaviour for all
clusters in the given range at the melting temperature. The distinct melting
behaviour of LJ42 was explained by the topology of the potential energy
surface by examining the isomer distributions at phase transitions for
LJ39-LJ55. The isomer distributions were found to be a useful way
to interpret this behaviour and melting dynamics in general. Melting
temperature, latent heat and entropy change upon melting values were
reported and are consistent with literature values and values calculated
from bulk thermodynamic properties. The dependence of these quantities on
the size of the clusters was examined and it is found that latent heat is
the key quantity to determine the magic numbers. 相似文献
14.
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
15.
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
16.
T. Mazza P. Piseri G. Bongiorno L. Ravagnan M. Amati M. Devetta C. Lenardi M. Coreno M. de Simone P. Milani 《Applied Physics A: Materials Science & Processing》2008,92(3):463-471
Synchrotron radiation-based experimental techniques are largely employed for the characterization of the reactivity of finite
size systems; in particular, x-ray absorption spectroscopy (XAS) is a suitable tool to shed light on the local electronic
structure and chemical status of atoms in nano-objects, as it is very sensitive to the local bonding environment of the probed
site. In supported clusters intrinsic properties and reactivity are largely distorted and obscured by the changes imposed
by the growth procedure and by the influence of the substrate, so the attainability of experiments on free clusters reacting
with species in the gas phase is a primary goal in the development of cluster science.
In this paper we report a proof of principle of the applicability of gas phase XAS technique to titanium and titanium oxide,
hydride and hydrate systems. Experiments are performed by coupling a pulsed microplasma cluster source (PMCS) with a third
generation synchrotron light source, and measuring the intensity of the electron yield coming from the interaction of VUV
photons with the clusters seeded in a supersonic beam. 相似文献
17.
J. Moc 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(3):309-317
We have explored the lowest doublet and quartet potential
energy surfaces (PES) for the reaction of gallium trimer with H2. This
reaction was studied experimentally by Margrave and co-workers in a noble
gas matrix. The detailed reaction paths ending up with the low-energy
Ga3H2 hydride isomers have been predicted based on the high level
ab initio coupled-cluster calculations (CCSD(T)) with large basis set. We
have found that the reaction occuring on the lowest doublet PES is described
by the activation barrier for H2 cleavage of about 15 kcal/mol,
consistent with experiment. In the most stable Ga3H2 hydride
structure, whose formation is exothermic by 15 kcal/mol, both H atoms assume
three-fold bridged positions. The diterminal planar structure of
Ga3H2, proposed experimentally from the observed IR spectra, is
found to be only 1 kcal/mol less stable than the dibridged form. 相似文献
18.
A. A. Koronovskii A. E. Hramov 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):447-452
We consider a type of intermittent behavior that occurs
as the result of the interplay between dynamical mechanisms giving
rise to type-II intermittency and random dynamics. We analytically
deduce the law for the distribution of the laminar phases, which has
never been obtained hitherto. The already known dependence of the
mean length of the laminar phases on the criticality parameter [Phys. Rev. E
68, 036203 (2003)] follows as a corollary of the carried out
research. We also prove that this dependence obtained earlier under
the assumption of the fixed form of the reinjection probability does
not depend on the relaminarization properties, and, correspondingly,
the obtained expression of the mean length of the laminar phases on
the criticality parameter remains
correct for different types of the reinjection probability. 相似文献
19.
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
20.
Y.-C. Lai K. Park L. Rajagopalan 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(1):65-70
We investigate a class of nonlinear wave equations subject to
periodic forcing and noise, and address the issue of energy optimization.
Numerically, we use a pseudo-spectral method to solve the nonlinear stochastic
partial differential equation and compute the energy of the system as a
function of the driving amplitude in the presence of noise.
In the fairly general setting where the system possesses two coexisting
states, one with low and another with high energy, noise can induce
intermittent switchings between the two states. A striking finding is that,
for fixed noise, the system energy can be optimized by the driving in a
form of resonance. The phenomenon can be explained by the Langevin dynamics
of particle motion in a double-well potential system with symmetry breaking.
The finding can have applications to small-size devices such as
microelectromechanical resonators and to waves in fluid and plasma. 相似文献