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1.
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
2.
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
3.
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
4.
5.
M.L. Gardel R. Vandenbosch B.P. Henry C. Cooper D.I. Will 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):79-81
The destruction cross-section for 22.5 and 50 keV C1- , for 10 and 50 keV C8
1- and for 50 and 75 keV C60
1- clusters in collisions with H2 has been measured by an attenuation method. The destruction of the cluster anions is dominated by electron detachment rather
than fragmentation and is of the order of the geometric cross-section. The cross-sections vary little with bombarding energy.
Received: 16 September 1998 / Received in final form: 23 February 1999 相似文献
6.
L. Dukan L. del Fabbro P. Pradel O. Sublemontier J.M. Mestdagh J.P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):257-265
Photofragmentation of Fe(H2O)n
+
clusters (n
=1-9) is investigated at three different wavelengths, 532, 355 and 266 nm. Two fragmentation pathways are observed depending essentially
on the photon energy, but also on the parent size n. The fragmentation products belong to two ion families, Fe(H2O)m
+
and FeOH(H2O)m
+
, which correspond to dehydration and intracluster dehydrogenation reactions respectively. The ion yields are studied as a
function of the laser fluence in order to determine the number of photons implied in the photofragmentation process. This
allows us to estimate that the D[(H2O)n-1Fe+-(H2O)] bond energy is ranging between 0.44 eV and 0.55 eV for .Photon absorption cross sections are also derived from the fluence experiments, and two different behaviors are observed:
i) At 355 nm, far away from any transition, progressive solvation of the metal ion results in an increasing absorption cross section from n
=2 to n
=9. This can be attributed to a forbidden transition of bare , which becomes progressively allowed because of the interaction with more and more water ligands. ii) At 266 nm, close to
several allowed transitions of bare , a distinct maximum is observed for the absorption of ion. It may be attributed to a change in the spin multiplicity when switching from and on one hand to Fe(H2O) on the other.
Received: 11 November 1997 / Revised: 18 February 1998 / Accepted: 22 April 1998 相似文献
7.
J.M. Weber E. Leber M.-W. Ruf H. Hotop 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(4):587-594
Using a high resolution laser photoelectron attachment method, we have studied the formation of (H
2
O)
q
- (q = 2, 6, 7, 11, 15) cluster ions in collisions of slow free electrons (E = 1-80 meV) and Rydberg electrons (n = 12-300) with water clusters. Resonances at zero energy have been observed, the shapes of which are strongly dependent on
cluster size. The results are discussed in terms of the formation of metastable negative ions.
Received 8 March 1999 相似文献
8.
J. Hüfner Y.B. He B.Z. Kopeliovich 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):239-244
Prompt gluons are an additional source for charmonium suppression in nuclear collisions, in particular for nucleus-nucleus
collisions. These gluons are radiated as bremsstrahlung in N-N collisions and interact inelastically with the charmonium states
while the nuclei still overlap. The spectra and mean number <n
g> of the prompt gluons are calculated perturbatively and the inelastic cross section σabs
Ψg is estimated. The integrated cross sections σ(A B →J/ψX) for p-A and A-B collisions and the dependence on transverse energy for S-U and Pb-Pb can be described quantitatively with
some adjustment of one parameter <n
g>σabs
Ψg.
Received: 20 August 1999 相似文献
9.
V. Kasperovich K. Wong G. Tikhonov V.V. Kresin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):99-102
An analysis of integral cross sections for slow electron collisions with neutral sodium clusters and nanoparticles reveals
that, in addition to an effective negative ion formation channel, there exists a strong inelastic threshold-type process which
appears above a collision energy of 1-1.3 eV. We show that it can be plausibly associated with the onset of direct electron-induced
cluster fragmentation. This result highlights the importance of understanding the dynamics of electron-vibrational energy
transfer in nanoclusters, including the relative probability of direct vs. statistical energy transfer.
Received 24 November 2000 相似文献
10.
P. Hvelplund B. Liu S. Brøndsted Nielsen S. Tomita 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):133-136
We have measured electron capture cross sections in collisions between
higher order fullerene anions Cn
- (n=76, 78, 82, 84, 86, 90 and 96) and
Na atoms. The ions were produced in an electrospray ion source (ESI) and accelerated to an energy of 50 keV. The measured
cross section for dianion formation is three times larger for C96 than that for C60. The latter cross section was earlier found to be 36 ?2. The dramatic increase of the cross section with fullerene size is explained by means of the curve crossing model for electron
transfer. 相似文献
11.
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
12.
V. M. Apatin V. N. Lokhman G. N. Makarov D. D. Ogurok A. N. Petin E. A. Ryabov 《JETP Letters》2013,97(12):697-703
The fragmentation of homogeneous (CF3I) n clusters (where n ≤ 45 is the average number of molecules in a cluster) in a molecular beam, as well as (CF3I) n clusters inside of large (Xe) m clusters (where m ≥ 100 is the average number of atoms in a cluster) or on their surface, by laser ultraviolet radiation has been studied. It has been found that the indicated three types of (CF3I) n clusters have different stabilities with respect to fragmentation and strongly different dependences of the fragmentation probability on the energy of ultraviolet radiation. Fragmentation at low energies and the weakest energy dependence of the probability of fragmentation are observed for homogeneous clusters, a stronger dependence is characteristic of (CF3I) n clusters localized inside (Xe) m clusters, and the strongest dependence is observed for (CF3I) n clusters on the surface of (Xe) m clusters. Possible reasons for such a character of the observed dependences have been discussed. 相似文献
13.
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
14.
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
15.
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
16.
B. H. Yanga P. C. Stancil 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(3):317-324
Quantum close-coupling and coupled-state approximation scattering calculations for rotational energy transfer of rotationally
excited CH4 due to collisions with He are presented for collision energies between 10−7 and 3000 cm−1 using the MP4 potential of Calderoni et al. [J. Chem. Phys. 121, 8261 (2004)]. State-to-state cross sections and rate coefficients
from selected initial rotational states of CH4 in symmetries A, E, and F are studied from the ultra-cold to the thermal regime. Comparison of the cross sections with available theoretical results
and experimental data show good agreement. Applications to astrophysics and cold laboratory environments are briefly addressed. 相似文献
17.
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
18.
19.
M. Vogel K. Hansen A. Herlert L. Schweikhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):73-76
The decay pathway competition between monomer and dimer evaporation of photoexcited cluster ions Au
+
n, n = 2-27, has been investigated by photodissociation of size-selected gold clusters stored in a Penning trap. For n > 6 the two decay pathways are distinguished by their experimental signature in time-resolved measurements of the dissociation.
For the smaller clusters, simple fragment spectra were used. As in the case of the other copper-group elements, even-numbered
gold cluster ions decay exclusively by monomer evaporation, irrespective of their size. For small odd-size gold clusters,
dimer evaporation is a competitive alternative, and the smaller the odd-sized clusters, the more likely they decay by dimer
evaporation. In this respect, Au
+
9 shows an anomalous behavior, as it is less likely to evaporate dimers than its two odd-numbered neighbors, Au
+
7 and Au
+
11. This nonamer anomaly is typical for copper-group cluster ions M
+
9 (M = Cu, Ag, Au) and a similar behavior is found in the anionic heptamers M
-
7. It is discussed in terms of the well-known electronic shell closing at n
e = 8 atomic valence electrons.
Received 2 November 2000 相似文献
20.
Ş. Erkoç H. Kökten Z. Güvenç 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):361-365
The fragmentation of water clusters, [(H
2
O)n;n = 2-8], have been investigated by using molecular-dynamics simulation method. In the simulations a polarizable-dissociable
potential energy function for water has been used. Particular attention has bee paid to investigate the effect of structural
properties and cluster size on the fragmentation.
Received 27 April 2000 and Received in final form 6 October 2000 相似文献