共查询到20条相似文献,搜索用时 156 毫秒
1.
W. Christen U. Even 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):87-90
This contribution addresses the inelastic interaction of positively charged molecular cluster ions with a solid surface at
kinetic energies up to 30 eV/molecule. We report experimental results on the scattering of mass-selected, protonated methanol
cluster cations (CH3OH)nH+, n = 4-32, off a diamond-coated silicon surface. In particular we provide fragment size distributions of methanol cluster ions
following their impact on the target, as well as surface-induced neutralization probabilities of methanol cluster ions as
a function of the size and the kinetic energy of the parent clusters.
Received 30 November 2000 相似文献
2.
G. E. Ntamack F. Chandezon B. Manil H. Lebius S. Tomita C. Guet M. G. Kwato Njock B. A. Huber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):153-156
Highly charged sodium clusters produced in collisions
between neutral clusters and multiply charged ions are formed
within a large range of temperatures and fissilities, and
identified by means of a high-resolution reflectron-type
time-of-flight mass spectrometer ( m/m
14000). The limit of stability of these charged clusters is
experimentally investigated, and the time-of-flight spectra are
compared with theoretical spectra based on Monte-Carlo
simulations. The results indicate that the maximum fissility
(X) of stable clusters is
approaching the Rayleigh limit (X = 1) for larger clusters sizes. It is
mainly limited by the initial neutral cluster temperature (
T 100 K) and the energy
transfer in the ionizing collision. In addition, the comparison
between the measured and simulated spectra suggests for high
cluster charges a multi-fragmentation process, in which most of
charge is emitted, creating low charged residual cluster ions. 相似文献
3.
The internal energy of small ammonia clusters in a supersonic beam and after scattering off LiF(100)
C. Menzel H. Zacharias 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):109-114
The photoionization efficiency (PIE) of neutral ammonia clusters is studied as a function of photon energy. From these curves
the internal energies of clusters in the incident supersonic beam and of clusters surviving after scattering off a LiF(100)
surface are derived. A supersonic expansion of ammonia seeded in He produces small clusters of various size but with uniform
kinetic energy of about 285 meV per monomer molecule. The mass distribution of clusters in the jet and of the scattered particles
is measured in a reflecting time-of-flight mass spectrometer by single photon photoionization using vacuum ultraviolet (VUV)
laser radiation tunable between
and
. In the incident beam the internal energies of clusters up to n = 15 do not vary significantly and amount to an average of about . After scattering off LiF(100) the internal energy of clusters up to n = 4 increases with fragment size and amounts to about half a monomer binding energy.
Received 18 October 1999 and Received in final form 10 December 1999 相似文献
4.
C. Bobbert C.P. Schulz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):95-97
Nam(H2O)n Clusters ( n = 1...200, m = 1...50) are formed in a recently build pick-up arrangement. Preformed water clusters traverse a sodium oven, where sodium
atoms are picked up. At low sodium vapour pressure ( < 1×10-4 mbar) pure Na(H2O)n clusters are observed in the mass spectra. At high sodium vapour pressure ( > 1×10-3 mbar) the water cluster pick up more than 50 Na atoms and reaction products Na(NaOH)n ( n = 2, 4...50) dominate the mass spectra. The even number of NaOH units in the products indicate that also in a finite cluster
the reaction occurs in pairs as in the macroscopic reaction.
Received 4 December 2000 相似文献
5.
Magnetism in Rh clusters under hydrostatic deformations 总被引:1,自引:0,他引:1
E.O. Berlanga-Ramırez F. Aguilera-Granja A. Dıaz-Ortiz A. Vega 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):343-349
The magnetic behavior of rhodium clusters RhN (N = 4-38) under hydrostatic deformations was investigated. The starting cluster structures were obtained from an evolutionary
search algorithm applied to a Gupta potential. The spin-polarized electronic structure and related magnetic properties were
calculated using a self-consistent spd tight-binding Hamiltonian within the unrestricted Hartree-Fock approximation. The magnetic behavior was analyzed in terms
of the interdependence between the geometrical parameters and the electronic structure. Anomalous magnetic effects were found
in some cases.
Received 5 August 2002 / Received in final form 10 January 2003 Published online 4 March 2003
RID="a"
ID="a"e-mail: berlanga@dec1.ifisica.uaslp.mx 相似文献
6.
Kellerbauer A. Blaum K. Bollen G. Herfurth F. Kluge H.-J. Kuckein M. Sauvan E. Scheidenberger C. Schweikhard L. 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(1):53-64
For a detailed study of the accuracy of the Penning trap mass spectrometer ISOLTRAP all expected sources of uncertainty were
investigated with respect to their contributions to the uncertainty of the final result. In the course of these investigations,
cross-reference measurements with singly charged carbon clusters 12C+
n were carried out. The carbon cluster ions were produced by use of laser-induced desorption, fragmentation, and ionization
of C60 fullerenes and injected into and stored in the Penning trap system. The comparison of the cyclotron frequencies of different
carbon clusters has provided detailed insight into the residual systematic uncertainty of ISOLTRAP and yielded a value of
8×10-9. This also represents the current limit of mass accuracy of the apparatus. Since the unified atomic mass unit is defined
as 1/12 of the mass of the 12C atom, it will be possible to carry out absolute mass measurements with ISOLTRAP in the future.
Received 7 June 2002 Published online 6 November 2002
RID="a"
ID="a"e-mail: a.kellerbauer@cern.ch
RID="b"
ID="b"Current address: Centre de Physique des Particules de Marseille, 13288 Marseille Cedex 9, France. 相似文献
7.
M. Ison P. Balenzuela A. Bonasera C.O. Dorso 《The European Physical Journal A - Hadrons and Nuclei》2002,14(4):451-457
In this communication we analyze the behavior of excited drops contained in spherical volumes. We study different properties
of the dynamical systems, i.e. the maximum Lyapunov exponent MLE, the asymptotic distance in momentum space d
∞ and the normalized variance of the maximum fragment. It is shown that the constrained system behaves as undergoing a first-order
phase transition at low densities while as a second-order one at high densities. The transition from liquid-like to vapor-like
behavior is signaled both by the caloric curves, the thermal response functions and the MLE. The relationship between the
MLE, d
∞, and the caloric curve is explored.
Received: 28 March 2002 / Accepted: 17 May 2002 相似文献
8.
K. Manninen M. Manninen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):243-249
Ground state geometries of small hard sphere clusters were studied using two different type of contact interaction, a pair-potential
and a many-atom interaction. Monte Carlo method in an FCC lattice with all possible (111) stacking faults was used to obtain
the minimum energy geometries for clusters up to 59 atoms. Due to the surface energy, FCC packing is generally favoured as
opposite to the HCP structure. However, in most cluster sizes the ground state obtained with the many-atom interaction has
one or more stacking faults. The most symmetric geometry is usually not the ground state. Clusters with 59 and 100 atoms were
studied due the possibility of a high symmetry cluster with stacking faults in all four directions. The size dependence of
the total energy has similarities with that of the average moment of inertia.
Received 6 February 2002 / Received in final form 11 April 2002 Published online 19 July 2002 相似文献
9.
K. Nagaya H. Murakami H. Iwayama Y. Ohmasa M. Yao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):69-72
The spectra of deep inner-core excited mixed rare-gas clusters were recorded by using electron ion coincidence (EICO) and
multi-hit momentum imaging (MHMI) techniques.
The EICO spectra for Ar99Kr1 clusters reveal that singly charged ions are emitted from the inner-core excited clusters in addition to the multiple charged
ions.
The dependence of the EICO spectra on photon energy and cluster size suggests that the holes created through vacancy cascade
on the krypton atoms are transferred to the surrounding atoms, and that the singly charged ions are the primary product of
the krypton photoabsorption.
Charge localization is suggested for the inner-core excited mixed rare-gas clusters from the analysis of the EICO peak width.
The MHMI measurements give us direct evidence for the strong charge migration from X-ray absorbing atoms to surrounding atoms.
The photon energy dependence of the PSD image for fragment ions suggests that the momentum of the fragment ions depends on
the number of charges generated by the vacancy cascade. 相似文献
10.
M.A. Lebeault J. Viallon J. Chevaleyre C. Ellert D. Normand M. Schmidt O. Sublemontier C. Guet B. Huber 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):233-242
We exposed small size-controlled lead clusters with a few hundreds of atoms to laser pulses with peak intensities up to 1015 W cm-2 and durations between 60 fs to 2.5 ps. We measured kinetic energies and ionic charge of fragments as a function of the laser
intensity and pulse duration. Highly charged Pbn+ ions up to n = 26 have been detected presenting kinetic energies up to 15 keV. For comparison with our experimental results, we have performed
simulations of the laser coupling with a cluster-sized lead nanoplasma using a qualitative model that was initially proposed
by Ditmire and co-workers at LLNL for the case of rare gas clusters. From these simulations we conclude that two mechanisms
are responsible for the explosion dynamics of small lead clusters. As already observed for large rare gas clusters (n = 106), fragments with charge states below +10 are driven by Coulomb forces, whereas the higher charged fragments are accelerated
by hydrodynamic forces. The latter mechanism is a direct consequence of the strong laser heating of the electron cloud in
the nanoplasma arising from a plasmon-like resonance occurring at n
e = 3n
c. In order to obtain an optimized laser-nanoplasma coupling, our results suggest that the plasma resonance should occur at
the peak intensity of the laser pulse. Due to inertial effects, even for such small-sized clusters, the observed optimum pulse
duration is in the order of 1 ps which is in good agreement with our theoretical results.
Received 18 March 2002 Published online 19 July 2002 相似文献
11.
C. Bobbert S. Schütte C. Steinbach U. Buck 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):183-192
The interaction of large ammonia and water clusters in the size range from <n> = 10 to 3 400 with electrons is investigated in a reflectron time-of-flight mass spectrometer. The clusters are generated
in adiabatic expansions through conical nozzles and are nearly fragmentation free detected by single photon ionization after
they have been doped by one sodium atom. For ammonia also the (1+1) resonance enhanced two photon ionization through the state with v = 6 operates similarly. In this way reliable size distributions of the neutral clusters are obtained which are analyzed in
terms of a modified scaling law of the Hagena type [Surf. Sci. 106, 101 (1981)]. In contrast, using electron impact ionization, the clusters are strongly fragmented when varying the electron
energy between 150 and 1 500 eV. The number of evaporated molecules depends on the cluster size and the energy dependence
follows that of the stopping power of the solid material. Therefore we attribute the operating mechanism to that which is
also responsible for the electronic sputtering of solid matter. The yields, however, are orders of magnitude larger for clusters
than for the solid. This result is a consequence of the finite dimensions of the clusters which cannot accommodate the released
energy.
Received 21 November 2001 相似文献
12.
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
13.
A. Shestopalova 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):331-337
What role does the nucleotide composition play in the process of formation of hydrated environment of nucleic acids? Can one
estimate the hydration of nucleic acids on the level of their components? In order to resolve these questions we have completed
an extensive computer simulation of the hydration of nucleic acids components - deoxynucleoside monophosphates distinguished
by nucleotide composition. The energetic characteristics of systems containing deoxynucleoside monophosphates and water clusters
of various dimensions are received. Our results demonstrate that deoxynucleoside monophosphates containing guanine and/or
cytosine residues hydrated more strongly because of formation of more hydrogen bonds with water molecules in small water clusters,
i.e. at low values of relative humidity. With increasing of number of water molecules in a water cluster the energetic preference
of deoxynucleoside monophosphates containing guanine and/or cytosine residues decreases, and for water clusters corresponding
to a state of a dilute aqueous solution the hydration of all types of deoxynucleoside monophosphates does not differ in a
great degree. Deoxynucleoside monophosphates containing guanine and/or cytosine residues cause the greater destruction of
the water structure compensated by the greater interaction with the nearest water molecules for all levels of relative humidity.
Received 25 December 2001 and Received in final form 22 March 2002 Published online 13 September 2002 相似文献
14.
S. Nonose S. Iwaoka H. Tanaka N. Okai T. Shibakusa K. Fuke 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):335-338
Photo-induced reaction of
[Fe(III)-protoporphyrin]+
(hemin+) ions solvated with
dimethylsulfoxide (DMSO) is investigated by using a tandem mass
spectrometer with electrospray ionization. We measure the
photodissociation yields of mass-selected
hemin+(DMSO)n
clusters for n = 0-3. The
mass spectra of the fragment ions show the -cleavage of
carboxymethyl groups in addition to the evaporation of solvent
molecules. Yield of the -cleavage reaction is found to depend
strongly on the excitation energy and the number of solvent
molecules. We also examine photo-induced reactions of
multiply-charged cytochrome c ions, (M + nH)n + (
n = 9-17). Photoionization is
found to be the dominant process for the lower charged states (
n = 9-12) and its yield
decreases rapidly with increasing the charge. The
photoionization is ascribed to the emission of electron by
multiphoton excitation of heme under the influence of Coulomb
attractive potential arising from the charges in the polypeptide
chain. Model calculations of the Coulomb potential suggest that
the structure of the polypeptide chain is completely elongated. 相似文献
15.
Z. Sosin R. Płaneta T. Ciszek J. Brzychczyk W. Gawlikowicz K. Grotowski S. Micek P. Pawłowski A. Wieloch A.J. Cole D. Benchekroun E. Bisquer A. Chabane M. Charvet B. Cheynis A. Demeyer P. Désesquelles E. Gerlic A. Giorni D. Guinet D. Heuer P. Lautesse L. Lebreton A. Lléres M. Stern L. Vagneron J.B. Viano 《The European Physical Journal A - Hadrons and Nuclei》2001,11(3):305-310
The shape of the velocity distributions of charged particles projected on the beam direction can be explained if emissions
from the hot projectile-like fragment and the target-like fragment are supplemented by an emission from an intermediate velocity
source located between them. The creation of this source is predicted by a two-stage reaction model where, in the second stage,
some of the nucleons identified in the first stage as participants form a group of clusters located in the region between
the colliding nuclei. The cluster coalescence process is governed on the average by the maximum value of entropy, although
its fluctuations are also significant. The properties of the intermediate velocity source are precisely described, including
the isotopic composition of the emitted particles.
Received: 12 March 2001 / Accepted: 20 June 2001 相似文献
16.
Dynamics of the plume formation and parameters of the ejected clusters in short-pulse laser ablation 总被引:2,自引:0,他引:2
L.V. Zhigilei 《Applied Physics A: Materials Science & Processing》2003,76(3):339-350
The dynamics of the early stages of the ablation plume formation and the mechanisms of cluster ejection are investigated in
large-scale molecular dynamics simulations. The cluster composition of the ablation plume has a strong dependence on the irradiation
conditions and is defined by the interplay of a number of processes during the ablation plume evolution. At sufficiently high
laser fluences, the phase explosion of the overheated material leads to the formation of a foamy transient structure of interconnected
liquid regions that subsequently decomposes into a mixture of liquid droplets, gas-phase molecules, and small clusters. The
ejection of the largest droplets is attributed to the hydrodynamic motion in the vicinity of the melted surface, especially
active in the regime of stress confinement. Spatially resolved analysis of the dynamics of the plume formation reveals the
effect of segregation of the clusters of different sizes in the expanding plume. A relatively low density of small/medium
clusters is observed in the region adjacent to the surface, where large clusters are being formed. Medium-size clusters dominate
in the middle of the plume and only small clusters and monomers are observed near the front of the expanding plume. Despite
being ejected from deeper under the surface, the larger clusters in the plume have substantially higher internal temperatures
as compared to the smaller clusters. The cluster-size distributions can be relatively well described by a power law Y(N)∼N-τ with exponents different for small, up to ∼15 molecules, and large clusters. The decay is much slower in the high-mass region
of the distribution.
Received: 13 October 2001 / Accepted: 18 July 2002 / Published online: 25 October 2002
RID="*"
ID="*"Corresponding author. Fax: +1-434/982-5660, E-mail: lz2n@virginia.edu 相似文献
17.
N. Pontius P.S. Bechthold M. Neeb W. Eberhardt 《Applied physics. B, Lasers and optics》2000,71(3):351-356
A femtosecond photo-electron experiment is described which provides excellent conditions for measuring time-resolved photo-electron
spectra of free, monodispersed cluster anions using repetition rates up to 100 Hz. Cluster anions are synthesized in an electric
arc and subsequently cooled in a helium carrier gas. A time-of-flight spectrometer is used for mass separation of the negatively
charged clusters. The kinetic energy of the photo-electrons is analyzed by a magnetic-bottle time-of-flight spectrometer,
which guarantees a maximum collection efficiency. Femtosecond laser pulses are generated by a seeded regenerative Ti:Sa amplifier,
which is externally pumped with the second harmonic of a diode-pumped solid-state Nd:YAG laser. A retroreflector mounted on
a computer-controlled translation stage serves as a reproducible time delay of the probe pulse. The high energy output of
the laser pulses (∼3 mJ) in combination with the variable repetition rate and the high stability of the amplified pulses provide
excellent conditions for recording pump-probe photo-electron spectra of mass-separated cluster anions even at the fairly low
ion density of pulsed plasma cluster sources. First results on the electron dynamics of the Pt3
- cluster demonstrate the reliability of the whole system. Further experimental investigations will concentrate on electron-relaxation
processes in transition- and noble-metal clusters as well as on the nuclear and transition-state dynamics of chemically reacted
adsorbate clusters.
Received: 7 January 2000 / Published online: 7 August 2000 相似文献
18.
P. Andersson C. Steinbach U. Buck 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):53-56
The structure of large water clusters of known size
distributions 〈n〉 = 20-2000
is investigated by vibrational spectroscopy of the OH stretch
mode. The water clusters are predissociated by a pulsed tunable
infrared optical parametrical oscillator (OPO) in the frequency
range 2800-3800 cm-1. Their fragments
are detected off-axis by electron impact ionization and mass
analyzed by a quadrupole mass spectrometer. The largest ion
signal stems from the neutral water hexamer fragment. The ion
yield is investigated at certain wavelengths while the size of
the clusters is varied, and for certain sizes complete
absorption spectra of the OH stretch motion are measured.
Fingerprints of the different coordination types of the water
molecules in the clusters are found and it turns out that our
method is especially sensitive to amorphous structures with
frequencies shifting in the range of 3300-3400
cm-1. 相似文献
19.
M.N. Huda A.K. Ray 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(2):217-227
The formalisms of many body perturbation theory and coupled cluster theory have been used to study the electronic and geometric
structures of neutral, cationic, and anionic small silver clusters. Hay-Wadt relativistic effective core potentials replacing
the twenty-eight core electrons and a Gaussian basis set have been used. Topologically different clusters and clusters belonging
to different symmetry groups have been identified and studied in detail. Full geometry optimizations have been carried out
at four different correlated levels of theories. Ionization potentials, electron affinities, and fragmentation energies of
the optimized clusters have been compared with other experimental and theoretical results available in the literature. No
convergence problems are encountered at the various levels of correlated theories. This is noteworthy since it has been claimed
in the literature that for d elements the MP series does not converge very well.
Received 16 April 2002 / Received in final form 12 September 2002 Published online 21 January 2003
RID="a"
ID="a"e-mail: akr@uta.edu 相似文献
20.
P. Farmanara H.-H. Ritze V. Stert W. Radloff I.V. Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):193-209
Neutral ammonia clusters (NH3)m are photo-excited to the electronic state by a deep UV femtosecond laser pump pulse. Within a few hundred femtoseconds a significant fraction of the clusters
rearrange to form an H-transfer state (NH3)m-2NH4(3s)NH2 with the subunit NH4 in its 3s electronic ground state. This state is then electronically excited by a time-delayed infrared control pulse of variable wavelength.
Finally, a third (probe) pulse in the UV ionizes the clusters for detection. The lifetime of the excited (NH3)m-2NH4(3p)NH2 states is found to vary between 2.7 and 0.13 ps depending on cluster size and excitation energy. It increases drastically
upon deuteration. The corresponding cluster size-dependent photoelectron spectra allow us to disentangle the underlying energetics
of the excitation and ionization process and reveal additional processes, such as nonresonant ionization or dissociative ionization.
The experimental findings suggest that the excited H-transfer ammonia complexes with m > 2 are deactivated by an internal conversion process back to the electronically lowest H-transfer state followed by fast
dissociation.
Received 22 September 2001 and Received in final form 31 January 2002 相似文献