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1.
2.
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
3.
C. Yannouleas U. Landman A. Herlert L. Schweikhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):81-85
Using Penning-trap experiments and a shell-correction method incorporating ellipsoidal shape deformations, we investigate
the formation and stability patterns of trianionic gold clusters. Theory and experiment are in remarkable agreement concerning
appearance sizes and electronic shell effects. In contrast to multiply cationic clusters, decay of the trianionic gold clusters
occurs primarily via electron autodetachment and tunneling through a Coulomb barrier, rather than via fission.
Received 9 January 2001 相似文献
4.
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
5.
K. Hamada T. Wada C. Guet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):359-368
Stability of highly charged metal clusters in the electric field of an external ion is investigated with the classical liquid
drop model. We study the optimum shape of the cluster which has a local minimum of the total energy, taking account of the
effects of the surface charge polarization on the Coulomb energy and the cluster deformation on the surface energy. We find
that the cluster deformation greatly affects the total energy of the system and that a cluster with a fissility larger than
some critical value 0.7-0.8 can become unstable against deformation. We investigate the local competition between the Coulomb
force and the surface tension at the cluster surface and show that the surface charge polarization which is induced by the
external electric field significantly affects the shape of the cluster and its stability.
Received 5 November 2002 / Received in final form 27 January 2003 Published online 11 March 2003
RID="a"
ID="a"e-mail: hamada@konan-u.ac.jp 相似文献
6.
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
7.
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
8.
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
9.
D. Ievlev I. Rabin W. Schulze G. Ertl 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):157-160
The Pick Up technique allows continuous formation of high density metal cluster beams in the otherwise hardly accessible size
range Me2 to about Me50. With an apparatus based on the use of cryo-condensation pumps, Ar as inert gas for production of the host clusters by adiabatic
expansion and silver as metal we demonstrate how the various source parameters influence the composition and mean size of
the resulting cluster distributions. The analysis in the gas phase by means fluorescence spectroscopy allows to conclude that
an Ar shell encapsulates the metal clusters.
Received 30 November 2000 相似文献
10.
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
11.
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
12.
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
13.
S. Pokrant J.A. Becker 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):165-168
Magnetic properties of isolated DyN clusters are studied in a molecular beam performing Stern-Gerlach experiments. The magnetizations μ
z
of DyN are measured in dependence of the magnetic field strength B
= 0-1.6 T and at nozzle temperatures T
n
= 18 K and T
n
= 300 K. At room temperature the magnetization augments linear with the field following a simple paramagnetic model. At T
n
= 18 K the magnetization curves saturate at field strengths B
≥0.8 T. To explain the magnetization process at low temperatures two models are discussed: A model for adiabatic magnetization
based on cluster rotation effects and a modified van-Vleck model.
Received 30 November 2000 相似文献
14.
15.
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
16.
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
17.
R.J. Tarento P. Joyes J. van de Walle 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):355-360
The present study focuses on electronic correlation effects on magnetic energy, the spin-spin correlation function of an octahedron
cluster in the (3↑, 3 ↓) electronic configuration threaded by a magnetic field. Some other spin configurations are also discussed
and various field directions are considered. An accurate diagonalisation technique has been used to solve the Hubbard Hamiltonian.
A result is analysed on a linear energy stabilisation at low magnetic flux. Moreover, two types of antiferromagnetic transition
versus the flux occurring for a correlation term larger than a critical one have been observed, i.e. the likelihood of a charge excitation before the antiferromagnetic transition. Finally, a comparison between the results
obtained from the exact diagonalisation and the Gutzwiller method has been carried out, leading to a suggested modification
of the Gutzwiller approach in order to improve it.
Received 23 June 1999 and Received in final form 28 July 2000 相似文献
18.
19.
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
20.
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