共查询到20条相似文献,搜索用时 15 毫秒
1.
J.M. Weber I.I. Fabrikant E. Leber M.-W. Ruf H. Hotop 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):247-256
Using laser photoelectron attachment to methyl iodide clusters in a differentially-pumped seeded supersonic helium beam and
mass spectrometric ion detection, we have measured the rate coefficients for formation of (q = 0-2) ions over the electron energy range 0-100 meV with an effective energy width of about 2.5 meV. Whereas a prominent
vibrational Feshbach resonance just below the onset for the C-I stretch vibration ( ) is observed for dissociative attachment to monomers (yielding I- ions), only weak and broad structure, shifted to lower energies, is detected for formation of ions and essentially no structure is left in the attachment spectrum for . These observations are interpreted by model R-matrix calculations which successfully describe the DA cross-section for the monomer and qualitatively recover the trend
observed for cluster ion formation. For the clusters, the effects of increased electron-target long-range interaction and
of solvation as well as coupling to soft vibrational modes lead to strong broadening and shifting of the vibrational Feshbach
resonance and, ultimately, to its disappearance.
Received 29 November 1999 and Received in final form 14 January 2000 相似文献
2.
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
3.
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
4.
Y. Tai J. Murakami C. Majumder V. Kumar H. Mizuseki Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):295-298
Fragmentation of germanium and tin cluster ions
in the low-energy
collisions with a Si surface has been investigated by means of a
tandem time-of-flight mass spectrometer. At low incident
energies, smaller clusters fragmented by an atom loss process,
whereas larger clusters decayed by fission. The favored
fragmentation paths for both cluster ions were similar to those
for Si cluster ions. The results support the structural
similarities among Si, Ge, and Sn clusters in the present size
range. For tin cluster ions, low-energy fragmentation patterns
were compared with those obtained from theoretical calculations
using generalized gradient approximation (GGA) and the B3PW91
exchange-correlation functional. It has been found that the
B3PW91 hybrid functional results are consistent with the
experimental observations. 相似文献
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.
Y. Ren R. Moro V. V. Kresin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):109-112
Individual amino acid molecules embedded in helium
nanodroplets fragment extensively when the beam is ionized by electron
bombardment. However, we find that when glycine and tryptophan are picked up
right after, or right before, a small amount of water, the mass spectra
become significantly altered. For glycine, the detected ions consist almost
entirely of intact protonated amino acids, with or without a few water
molecules attached. In other words, the presence of water exerts a striking
“buffering” effect on the ionization-induced fragmentation. For tryptophan
the effect is weaker but also present. In both cases, the hydroxyl group
lost upon ionization overwhelmingly comes from the water partner (in strong
contrast to the situation observed when amino acids are picked up by neat
water clusters). A complementary experiment involving DCl molecules
co-embedded with water shows that in this case Cl and/or DCl invariably
leave the droplet upon ionization. The observed patterns may be steered by
the analytes' dipole moments or by solvation effects. 相似文献
7.
C. Becker J. Gspann R. Krämer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):301-304
Reactive accelerated cluster erosion (RACE) of single crystal artificial diamond has been used to fabricate various nano-
and microstructures. Carbondioxide clusters of about 1000 molecules are accelerated to 100 keV to act as the eroding agent.
Using movable shadow masks, the accelerated cluster beam may erode staircase structures acting as an optical grating. A cycloid
gear has been generated via a stationary nickel mask. Non-reactive accelerated cluster erosion using argon clusters will be considered for comparison.
Received 30 November 2000 相似文献
8.
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
9.
W. Shi S. Böhm C. Böhme C. Brandau A. Hoffknecht S. Kieslich S. Schippers A. Müller C. Kozhuharov F. Bosch B. Franzke P.H. Mokler M. Steck Th. Stöhlker Z. Stachura 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):145-154
Recombination of fully stripped U92+ ions with electrons has been investigated at the Experimental Storage Ring (ESR) in Darmstadt. Absolute recombination rate
coefficients have been measured for relative energies from 0 to 33 eV. For energies greater than 20 meV the experimental result
is well described by the theory for radiative recombination (RR). Below 20 meV the experimental rate increasingly exceeds
the RR calculation as observed previously in the recombination of light bare ions as well as of Bi83+. This low-energy rate enhancement is shown to scale as Z2.6 for bare ions, where Z is the atomic number of the ion. The U92+ recombination rate enhancement is insensitive to changes of the electron density. Variation of the magnetic guiding field
strength from 80 mT to 120 mT resulted in oscillations of the recombination rate at 0 eV. The oscillations are partly attributed
to changes of the transverse electron temperature accompanying the change of the magnetic guiding field strength; partly they
may be caused by uncompensated small changes of the interaction angle between the two beams.
Received 1st March 2001 and Received in final form 20 April 2001 相似文献
10.
S. Martin J. Bernard L. Chen A. Denis J. Désesquelles 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):1-6
Electron capture by Ar8+ in collisions with C60 fullerene has been investigated using coincident measurements of the number n of ejected electrons, the mass and charge of multicharged Cr+
60
recoil ions and their fragments Ci+
m and the final charge state of outgoing projectiles Ar(8-s)+ (). The number of captured electrons r is the sum of the numbers of stabilized and emitted electrons: r
=
n
+
s. The ratio n
/
s decreases by a factor three with s increasing from 1 to 7 showing that the multiply excited states populated by capture of a large number of electrons are rather
stable against auto-ionisation. Each kinetic energy spectrum of Ar+ and Ar2+ projectiles is composed of two peaks which we attribute to collisions “inside” and “outside” the C60 cage. The measured energy shift of the projectile keV is consistent with the corresponding energy loss keV in a carbon foil with an equivalent thickness. Inside collisions are characterized by a strong dissociation of recoil
ions into light monocharged fragments and by a high multiplicity of ejected electrons.
Received: 25 March 1998 / Received in final form and Accepted: 9 June 1998 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.
K. Hashimoto M. Okamoto K. Takayanagi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):75-78
The stability of neutral, singly and multiply ionized silicon clusters, (N
= 2-7, M
= 0, , , ), has been investigated using an ab initio density functional method. We show that the fragmentation effect significantly affects the structure of mass-spectra of multiply
ionized silicon clusters. For clusters, the clusters with a large fragmentation energy are found to correspond to the high peaks at N = 4 and 6 in mass-spectra. For clusters, a peak at N = 5 in mass-spectra has been predicted to be especially high.
Received: 9 June 1997 / Revised: 8 January 1998 / Accepted: 25 February 1998 相似文献
13.
K. Guch J. Fedor S. Matt-Leubner R. Parajuli C. Mair A. Stamatovic O. Echt C. Lifshitz J. Harvey F. Hagelberg Z. Herman M. Probst P. Scheier T. D. Märk 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):131-136
The recent addition of (i) a third sector field to our two
sector field mass spectrometer (resulting in a BE1E2 field
configuration) and of (ii) a high performance electron gun
enables us now to study in detail the time dependence of the
kinetic energy release distribution (KERD) over a relatively
wide range of cluster ion lifetimes. Using this newly
constructed device we have studied here for the first time KERDs
and deduced binding energies BEs (using finite heat bath theory)
of large rare gas cluster ions (an upper size limit in earlier
studies arose from the fact that different naturally occurring
isotopes will contribute to a chosen metastable peak when the
size exceeds a certain value) and in addition of fullerene ions
smaller and larger than
(here again contaminating
coincidences did not allow such studies earlier). Moreover, high
precision KERD measurements for the decay of rare gas dimer ions
in conjunction with model calculations (using recently
calculated potential energy curves for the rare gas dimer ions)
also enable us to obtain information on the dynamics and the
mechanisms of the underlying spontaneous decay reactions
. In addition, we are also reporting
here a novel method (unified breakdown graph method) to
determine cluster ion binding energies using a recently
constructed tandem mass spectrometer BESTOF allowing us to
measure fragmentation patterns arising from the unimolecular
decay of molecular cluster ions induced by surface collisions.
The fragmentation and reaction patterns of protonated ethanol
cluster ions investigated here clearly demonstrate in contrast
to some of the earlier cluster ion studies that unimolecular
dissociation kinetics determines the formation of product ions
in the surface-induced decomposition. 相似文献
14.
L. Schweikhard K. Hansen A. Herlert G. Marx M. Vogel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):137-143
Ion traps are wall-less containers which allow the
extended storage of selected species. During the storage various
interaction steps may be repeatedly applied. To this end no
further hardware has to be added - in contrast to beam
experiments. In this progress report two examples of recent
developments are presented: the experiments have been performed
with metal clusters stored in a Penning (ion cyclotron
resonance) trap. A new experimental scheme has been developed
which allows precision measurements of the dissociation energies
of polyatomic species. It has been triggered by investigations
on the delayed photodissociation of stored metal clusters.
However, the technique is also readily available for application
to a broad variety of different species and it is not even
restricted to trapping experiments. The second development is
more closely connected with ion storage in Penning traps: by
application of an electron bath singly charged anionic
clusters can be converted into multiply charged species.
Subsequently, they are charge selected and investigated with
respect to their reaction upon excitation. In particular,
preliminary results indicate that dianionic metal clusters emit
two electrons upon photoexcitation whereas the singly charged
species show dissociation. 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.
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
17.
18.
R. S. Berry 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):5-6
We review some of the ways clusters offer special kinds
of insights both into properties of bulk matter and properties unique to
small systems. We then survey some of the tantalizing open questions that
lie ahead in cluster science. 相似文献
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.
M. Vogel K. Hansen A. Herlert L. Schweikhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):163-166
The dimer dissociation energies of gold cluster ions Au
+
n
, n
= 9, 11, 13, 15 have been determined with an extension of a recently developed model-independent method. Monomer-dimer decay
pathway branching ratios provide the energy dependent process which is needed in this method. The measured values are D
2
(
Au
+
9
) = 3.66(8)(9) eV, D
2
(
Au
+
11
) = 4.27(11)(8) eV, D
2
(
Au
+
13
) = 4.50(9)(7) eV and D
2
(
Au
+
15
) = 4.29(10)(6) eV.
Received 13 May 2002 / Received in final form 22 July 2002 Published online 24 September 2002
RID="a"
ID="a"e-mail: manuel.vogel@uni-mainz.de 相似文献