共查询到20条相似文献,搜索用时 46 毫秒
1.
T. Rander M. Lundwall A. Lindblad G. Öhrwall M. Tchaplyguine S. Svensson O. Björneholm 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):253-257
Resonant Auger spectra of O2 clusters excited at the O1s edge are reported. After excitation to the repulsive 1s-13σ* state, the resulting resonant Auger spectrum displays features that remain constant in kinetic energy as the photon energy
is detuned. The shift between known atomic fragment features and these features is consistent with that observed for atoms
and clusters in singly charged states in direct photoemission. These findings are strong evidence for the existence of molecular
ultrafast dissociation processes within the clusters or on their surface. 相似文献
2.
A. C. Reber S. N. Khanna J. S. Hunjan M. R. Beltran 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):221-224
Theoretical electronic structure studies on (ZnO)n (n= 2–18, 21) have
been carried out to show that the transition from an elementary ZnO molecule
to the bulk wurtzite ZnO proceeds via hollow rings, towers, and cages. Our
first principles electronic structure calculations carried out within a
gradient corrected density functional framework show that small
ZnnOn (n=2–7) clusters form single, highly stable rings.
Zn3O3 and the symmetric cage Zn12O12 are shown to be
particularly stable clusters. Among larger clusters, the most stable are
oblong cages, Zn15O15, Zn18O18, and Zn21O21,
which are reminiscent of nanotubes. 相似文献
3.
F.O. Talbot J.P. Simons 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):389-398
Mass-resolved resonant two photon ionisation (R2PI) and infrared ion dip spectra have been recorded for 4-phenylimidazole
(4PI) and its singly and multiply hydrated clusters 4PI(H2O)n = 0 - 4, under supersonic expansion conditions. In the case of 4PI(H2O)0,1, it has also been possible to record infrared spectra in both the ground (S0) and excited (S1) states. Combining the experimental data with the results of ab initio calculations has led to the structural assignment of each cluster. In each case, the water molecules bind primarily to the
NH site of the imidazole ring. Clusters with n≥ 2 incorporate linear water chains, in which the proton donating terminus bridges either to the π-electron system (n = 2) or to the >N: atom site (n = 3, 4) on the imidazole ring. Despite the creation of a “water wire”, connecting the donor and acceptor sites of imidazole,
there is no evidence of proton transfer in either the ground or excited state.
Received 20 December 2001 Published online 13 September 2002 相似文献
4.
A. Chaudhuri M. Block S. Eliseev R. Ferrer F. Herfurth A. Martín G. Marx M. Mukherjee C. Rauth L. Schweikhard G. Vorobjev 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(1):47-53
A carbon-cluster ion source has been installed and tested
at SHIPTRAP, the Penning-trap mass spectrometer for precision mass
measurements of heavy elements at GSI. Carbon-cluster ions
12Cn
+, 5 ≤n ≤23, were produced by
laser-induced desorption and ionization from
a
carbon sample. They
were tested for the first time as reference ions in an on-line mass
measurement of the radionuclides 144Dy, 146Dy and
147Ho. In addition, carbon clusters of various sizes were used
for an investigation of the systematic uncertainty of SHIPTRAP
covering a mass range from 84 u to 240 u. The mass-dependent
uncertainty was found to be negligible for the case of
(m-m ref)< 100 u. However, a systematic uncertainty of 4.5
×10-8 was revealed. 相似文献
5.
E. M. Fernández G. Borstel J. M. Soler L. C. Balbás 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):245-248
The ionic and electronic structure of
(Al2O3)n(Ox)
clusters with n
16 and x
= 0,
1, 2 is studied by means of first principles density functional
calculations, norm-conserving pseudopotentials and a numerical
atomic basis set. The equilibrium geometries have been
determined by total energy minimization, starting with several
initial geometries for each cluster size. The trends obtained
for the atomic arrangements (structural isomers, coordination
numbers, disordered versus
ordered structures, etc.) and the electronic properties
(binding energies, Homo-Lumo gap and dipole moments) are
discussed. For most of the oxidized clusters studied here we
find that the Homo-Lumo gap and the magnitude of dipole moment
of isomeric species can vary drastically. 相似文献
6.
A. Herlert L. Schweikhard M. Vogel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):65-68
Singly charged silver-cluster anions are produced in a laser vaporization source and transferred into a Penning trap. After
size selection the clusters are subjected to an electron bath in the trap, which results in the attachment of further electrons.
The relative abundance of dianions or trianions as a function of the clusters' size is analyzed by time-of-flight mass spectrometry.
Silver-cluster dianions are observed for sizes n≥ 24 and trianions for n > 100. In addition, a detailed study of the cluster sizes 24 ?n? 60 shows a pronounced resistance to electron attachment for singly charged anions Agn
- with a closed electronic shell, in particular Ag29
-, Ag33
-, and Ag39
-. Both the threshold size for the observation of dianionic silver clusters and the shell effects in the production yield correlate
favorably with previous theoretical investigations of the respective electron affinities.
Received 24 November 2000 相似文献
7.
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
8.
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
9.
C. Bréchignac Ph. Cahuzac B. Concina J. Leygnier I. Tignères 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):185-192
The cross-sections for collisional charge transfer between singly charged free clusters M
n
+ (M = Li, Na; n=1...50) and atomic targets A (cesium, potassium) have been measured as a function of collisional relative velocity in laboratory
energy range 1–10 keV. For each cluster size, the experimental values of the charge transfer cross-section are fitted with an universal parametric curve with two independent parameters and vm, the maximum cross-section and the corresponding velocity. For small size clusters (), the characteristic parameters show strong variations with the number of atoms in the cluster. Abrupt dips observed for n=10 and n=22 are attributed to electronic properties. Charge transfer patterns observed for various collisional systems present similarities,
which appear more sensitive to cluster quantum size effects than to collision energy defects. In their whole, the and vm parameters show differences in both their size evolution and their absolute values discussed in term of projectile and target
electronic structures.
Received 13 April 2000 and Received in final form 29 June 2000 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.
B. Klipp M. Grass J. Müller D. Stolcic U. Lutz G. Ganteför T. Schlenker J. Boneberg P. Leiderer 《Applied Physics A: Materials Science & Processing》2001,73(5):547-554
A PACIS (pulsed arc cluster-ion source) developed for high average cluster-ion currents is presented. The performance of the
PACIS at different operational modes is described, and the suitability for cluster-deposition experiments is discussed in
comparison with other cluster-ion sources. Maximum currents of mass-selected cluster ions of 3–6 nA of small Sin
- (n=4–10) clusters and 0.3–0.5 nA of large Aln
+/- (n=20–70) clusters are achieved. The mass-selected cluster ions are soft-landed on a substrate at residual kinetic energies
lower than 1 eV/atom, and the samples are characterized by X-ray photoelectron spectroscopy and scanning tunneling microscopy.
First results on the soft landing of “magic” Si4
- clusters on graphite are presented.
Received: 30 May 2001 / Accepted: 14 June 2001 / Published online: 2 October 2001 相似文献
12.
M. Bertolus V. Brenner P. Millié 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):387-394
An ab initio study of the Nan(OH)n, Nan(OH)n-1
+, Agn(OH)n, and Agn(OH)n-1
+ clusters with n up to four is presented. The results of this study show that, in accordance with experimental observations, the sodium hydroxide
clusters are almost purely ionic, while the Ag-O bond exhibits a significant covalent character. The perturbation caused by
the non-spherical OH- group relatively to an atomic anion, as well as the influence on structures and energies of the covalent character of the
metal-oxygen bond are determined. The appearance of metal-metal bonds in the silver hydroxide clusters is also discussed.
Finally, the theoretical results obtained on the Na-OH clusters are compared to experimental results available on the dissociation
of the Nan(OH)n-1
+ clusters.
Received 9 August 1999 and Received in final form 1st December 1999 相似文献
13.
A. Heidenreich I. Last J. Jortner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):195-202
We present a theoretical and computational study of the properties and the
response of the nanoplasma and of outer ionization in Xen clusters (n =
55–2171, initial cluster radius R0 = 8.7–31.0 ?) driven by
ultraintense near-infrared laser fields (peak intensity IM = 1015–1020 Wcm-2, temporal pulse length τ= 10–100 fs, and frequency ν= 0.35 fs-1). The positively charged high-energy nanoplasma produced by inner ionization nearly follows the oscillations of
the fs laser pulse and can either be persistent (at lower intensities of IM = 1015–1016 Wcm-2 and/or for larger cluster sizes, where the electron energy distribution is nearly thermal) or transient (at higher intensities
of IM = 1018–1020 Wcm-2 and/or for smaller cluster sizes). The nanoplasma is depleted by outer ionization that was semiquantitatively described by
the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity and pulse length
dependence of the outer ionization yield. The electrostatic model was further utilized for estimates of the laser intensity
and pulse
width dependence of the border radius R0
(I) for the attainment of complete outer ionization at
,
while at R0 > R0
(I) a persistent nanoplasma prevails. R0
(I)
establishes an interrelationship between electron dynamics and nuclear Coulomb explosion dynamics in ultraintense
laser-cluster interactions. 相似文献
14.
Metastable fragmentation of silver bromide clusters 总被引:2,自引:0,他引:2
J.-M. L'Hermite F. Rabilloud L. Marcou P. Labastie 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):323-330
The abundance spectra and the fragmentation channels of silver bromide clusters have been measured and analyzed. The most
abundant species are AgnBrn - 1
+ and AgnBrn + 1
- and Ag14Br13
+ is a magic number, revealing their ionic nature. However, some features depart from what is generally observed for alkali-halide
ionic clusters. From a certain size, AgnBrn - 1
+ is no more the main series, and AgnBr n - 2, 3
+ series become almost as important. The fast fragmentation induced by a UV laser makes the cations lose more bromine than
silver ions and lead to more silver-rich clusters. Negative ions mass spectra contain also species with more silver atoms
than required by stoichiometry. We have investigated the metastable fragmentation of the cations using a new experimental
method. The large majority of the cations release mainly a neutral Ag3Br3 cluster. These decay channels are in full agreement with our recent ab initio DFT calculations, which show that Ag+-Ag+ repulsion is reduced due to a globally attractive interaction of their d orbitals. This effect leads to a particularly stable trimer (AgBr)3 and to quasi-planar cyclic structures of (AgBr)n clusters up to n = 6. We have shown that these two features may be extended to other silver halides, to silver hydroxides (AgOH)n, and to cuprous halide compounds.
Received 9 November 2000 and Received in final form 25 January 2001 相似文献
15.
R. von Pietrowski K. von Haeften T. Laarmann T. Möller L. Museur A. V. Kanaev 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):323-336
The electronic and geometric structure of rare gas clusters doped with
rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation
spectroscopy in the VUV spectral range. Several absorption bands are
observed in the region of the first electronic excitations of the impurity
atoms, which are related to the lowest spin-orbit split atomic 3P1
and 1P1 states. Due to influence of surrounding atoms of the
cluster, the atomic lines are shifted to the blue and broadened
(“electronical cage effect”). From the known interaction potentials and
the measured spectral shifts the coordination of the impurity atom in
ArN, KrN, NeN and HeN could be studied in great detail.
In the interior of KrN and ArN the Xe atoms are located in
substitutional sites with 12 nearest neighbours and internuclear distances
comparable to that of the host matrix. In NeN and HeN the cluster
atoms (18 and 22, respectively) arrange themselves around the Xe impurity
with a bondlength comparable to that of the heteronuclear dimer. The results
confirm that He clusters are liquid while Ne clusters are solid for N≥
300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is
strong, small Rgm-clusters (Rg = Xe, Kr, Ar, m≤10 2) are formed
in the interior sites of the host cluster made of Ne or He. Specific
electronically excited states, assigned to interface excitons are observed.
Their absorption bands appear and shift towards lower energy when the
cluster size m increases, according to the Frenkel exciton model. The
characteristic bulk excitons appear in the spectra, only when the cluster
radius exceeds the penetration depth of the interface exciton, which can be
considerably larger than that in free Rgm clusters. This effect is
sensitive to electron affinities of the guest and the host cluster. 相似文献
16.
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
17.
T. Döppner J. P. Müller A. Przystawik J. Tiggesbäumker K.-H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):261-266
Silver clusters embedded in helium nanodroplets are
exposed to intense femtosecond laser pulses (1013 - 1016 W/cm2).
The signal of highly charged (q≤11) atomic fragments is maximized by
delayed plasmon enhanced ionization using stretched laser pulses. Further
details with respect to the dynamics of the charging process can be obtained,
when the intensity distribution within the laser focus is taken into
account. For the first time, the z-scan method is applied to clusters
which offers a route to investigate the explicit dependence of the ion signals
with respect to the laser intensity. By taking advantage of the volumetric
weighting effect ionization thresholds are determined, yielding values well
below 1014 W/cm2 for Agq+ ions with q≤11. 相似文献
18.
B. Kalita R. C. Deka 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(1):51-58
Density functional calculations have been performed to investigate CO adsorption on neutral, cationic and anionic Pdn (n=1–7) clusters. From the results, it is observed that the binding of CO molecule to neutral and cationic palladium clusters
takes place via 1-, 2- and 3-fold coordination. On the other hand, only terminal adsorption of CO molecule is possible in
anionic clusters barring bridging adsorption in Pd7
- cluster. 相似文献
19.
A. Kanaev L. Museur F. Edery T. Laarmann T. Möller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):261-268
We have studied the fluorescence of electronically excited OH*, H* and H2O+* dissociation fragments after VUV excitation ( h
ν≥11.6
eV) of rare-gas clusters (Rg = Ne, Ar) doped with H2O molecules. In contrast to a free molecule, where Balmer H-series dominate the UV-visible spectra, only the OH
*
(
A
2
Σ
+
↦
X
2
Π) emission band is observed in neon clusters. No emission of excited water ions has been observed. We find that while higher
excitation energies (Ne vs. Ar) induce higher vibrational excitation of the OH*
(
A
) fragment, the rotational temperature is lower. This effect is attributed to the difference in the geometric position of the
H2O molecule on the surface or inside the Rg-cluster. The rotational relaxation in neon clusters is rapid while the vibrational
relaxation is slow because of the coupling with the low energy matrix phonons.
Received 7 March 2002 / Received in final form 27 May 2002 Published online 19 July 2002 相似文献
20.
M. B. Torres L. C. Balbás 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):217-220
We present a first-principles pseudopotential optimization of
the lower energy equilibrium structure of SinSc- anions for
n=14-18. We find that Si16Sc- is more stable than its
neighbors clusters, in agreement with recent experimental mass spectra. We
also optimize the geometry of pure Sin neutral clusters in the range
n=14-18, and compare our results with those from previous
first-principles calculations. 相似文献