共查询到20条相似文献,搜索用时 31 毫秒
1.
G.M. Koretsky M.B. Knickelbein 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(3):273-278
The photoionization spectra of Pr2-Pr21 and Ce2-Ce17 have been measured near threshold. The ionization potentials (IPs) of and vary discontinuously with size, but trend downward toward the work function of the bulk metals. In general, the IPs of cerium
clusters display more variation than those of praseodymium clusters. The sudden discontinuities observed in the IPs of both
and is akin to that displayed by clusters of transition metal atoms, suggesting that as in transition metal clusters, the rapid
evolution in geometric structure with size is the source of these discontinuities.
Received: 2 January 1998 / Accepted: 10 March 1998 相似文献
2.
G. Mattei F. Toigo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):245-256
The effect of non-local norm-conserving pseudo-potentials on the static and dynamic properties of Nan and Lin cluster with n=6,8 is investigated in the frame of self-consistent LDA calculations with spherically averaged ionic density (SAPS model).
A comparison with previous calculations which use local pseudo-potentials as well with uniform averaged non-local pseudo-jellium
calculation has been carried out. A better quantitative agreement with experiments has been found in the calculation of the
photoresponse cross-section with respect to either simple jellium or pseudo-jellium model, even in very small clusters, where
deviations from sphericity are not negligible.
Received: 3 March 1998 / Received in final form and Accepted: 2 June 1998 相似文献
3.
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
4.
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
5.
R. Guirado-López D. Spanjaard M.-C. Desjonquères A.M. Oleś 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):437-446
We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (Oh) and icosahedral (Ih) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence
of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of
Oh and Ih clusters as a function of the atomic number along the 4
d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior
as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations.
Received: 20 November 1997 / Received in final form: 9 March 1998 / Accepted: 30 March 1998 相似文献
6.
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
7.
J. Lermé B. Palpant B. Prével E. Cottancin M. Pellarin M. Treilleux J.L. Vialle A. Perez M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):95-108
The optical response of free and matrix-embedded gold metal clusters AuN is investigated in the framework of the time-dependent local-density-approximation (TDLDA). The characteristics of the surface
plasmon resonance are carefully analyzed as a function of the model parameters and the particle radius. The strong influence
of the frequency-dependence of the 5d core-electron dielectric function in the vicinity of the interband threshold is emphasized. The size evolution of the Mie-frequency
in free gold clusters exhibits a noticeable blue-shift trend as the particle size decreases, much stronger than in silver
clusters. The width and shape of the resonance, essentially ruled by the decay via the interband transitions, are found closely correlated to the imaginary component of the core-electron dielectric function.
In presence of a surrounding matrix the blue-shift trend is largely rubbed out. Agreement with recent experimental results
on size-selected gold clusters embedded in an alumina matrix may be achieved by taking into account the porosity effects at
the metal/matrix interface. The comparison with the predictions of classical models is also provided.
Received: 9 March 1998 / Revised: 5 June 1998 / Accepted: 3 July 1998 相似文献
8.
K. Ohshimo H. Tsunoyama F. Misaizu K. Ohno 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):107-110
Intracluster electron transfer and oligomerization reaction were investigated by mass spectrometry of clusters of alkali metal
atom (M) with acrylonitrile (AN; CH2=CHCN). In the photoionization mass spectra of M(AN)n, magic numbers were clearly observed at n = 3k (k = 1-4 for M = Na and K, k = 1 for M = Li). The results of photodissociation of neutral K(AN)n indicate that the n = 3 cluster has an anomalous stability relative to other sizes of clusters. The C=C bond in vinyl molecules is also found
to be necessary to form the magic numbers by measuring the photoionization mass spectrum of K atom with propionitrile. These
results strongly support the intracluster anionic oligomerization reaction initiated by electron transfer from the alkali
atom. The quantum chemical calculations have revealed that the evaporation induced by excess energy generated by intracluster
oligomerization is important to form the magic numbers in the present clusters.
Received 29 November 2000 相似文献
9.
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
10.
The stability and electronic properties of the Rh-doped ruthenium clusters and their reactivity towards NH3 molecule have been studied using DFT calculations with the BLYP-D3/SDD level of theory. The results show that the doping of Ru clusters with Rh atom improves the catalytic performances of pure Ru clusters, and the Ru5Rh and Ru7Rh clusters are assumed to be less reactive than their neighbours. The interaction of NH3 with clusters exhibits that the Ru atoms are preferred adsorption sites for the NH3 molecule, and the adsorption takes place between the Ru atom of clusters and the N atom of NH3 molecule. The adsorption energies of NH3 on RunRh clusters are in the range of ?101.5 to ?218.4?kJ?mol?1, suggesting a strong adsorption between both species. Upon adsorption process, the electronic properties of the RunRh clusters were substantially changed. The variation of Eg (ΔEg) for the RunRh (n?≥?7) clusters is very important (ΔEg?≥?55%), suggesting that these clusters are very sensitive to the NH3 molecule. Hence, these clusters can be employed as nanosensors for the detection of the NH3 gas. 相似文献
11.
J. Akola A. Rytkönen H. Häkkinen M. Manninen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(1):93-99
The ionization potential of sodium clusters () at a finite temperature is studied using density functional theory and ab initio molecular dynamics. The threshold regions of the photoionization efficiency curves are deduced from the integrated IP distributions,
which are obtained from the energy eigenvalues of the highest occupied Kohn-Sham states during molecular dynamics by applying
a theoretically well-defined shift. The calculated ionization potentials are directly compared to the experimental values.
The energetically best geometry of Na55 is found to be a slightly distorted icosahedron.
Received 16 April 1999 and Received in final form 6 July 1999 相似文献
12.
J. Sun G. Yu Y. Jiang S. Zhang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):83-88
The additivity rule is employed to obtain the total (elastic+inelastic) cross-sections for positron scattering from molecules
including a number of diatomic, polyatomic molecules (H2, N2, HCl, CO2, NH3, SF6, CH4, C2H4 and C3H8) over an incident energy range of 10-1000 eV. The total cross-sections (TCS) of the constituent atoms of molecules are obtained
by employing a complex optical model potential (composed of static, polarization and absorption potential). The present results
are compared with experimental data and other theoretical calculations, good agreement is obtained in intermediate- and high-energy
region.
Received: 11 November 1997 / Revised: 23 March 1998 / Accepted: 16 June 1998 相似文献
13.
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
14.
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
15.
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
16.
E. Luc-Koenig M. Aymar M. Millet J.-M. Lecomte A. Lyras 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(2):205-223
We have investigated theoretically the asymmetrical photoionization yields into the 6s
1/2, 5d
3/2 and 5d
5/2 continuum channels of atomic barium observed by Wang, Chen and Elliott [Phys. Rev. Lett. 77, 2416 (1996)] in the study of coherent control through two-color resonant interfering paths. The atomic parameters obtained
from a theoretical approach based on a combination of jj-coupled eigenchannel R-matrix and Multichannel Quantum Defect Theory are used to analyze the photoionization spectra from the and 6s7p
states with polarized light beams. The studied energy range includes the 6p7p autoionizing resonances. The dynamics of the two-color photoionization is governed by the coherent excitation of the 6s6p and intermediate states. This excitation is described as an adiabatic process in the rotating wave approximation. The influence
of the radiative decay, spatial distribution of the intensities of the laser beams and hyperfine interaction is discussed.
Received 28 September 1999 相似文献
17.
D.D. Nelson M.S. Zahniser J.B. McManus C.E. Kolb J.L. Jiménez 《Applied physics. B, Lasers and optics》1998,67(4):433-441
2 O, and NO2 emissions have been measured with this instrument. The system is also capable of measuring CO, NH3, H2CO, CH3OH, and other small molecules in vehicle exhaust.
Received: 18 May 1998/Revised version: 1 July 1998 相似文献
18.
J.M. Mestdagh M. Berdah N. Auby C. Dedonder-Lardeux C. Jouvet S. Martrenchard-Barra D. Solgadi J.P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):291-302
The photodissociation of a chlorine molecule in the environment of a xenon cluster has been studied experimentally using the
real time pump and probe technique through the formation of an XeCl reaction product. The photodissociating system is probed
in such a way that the movement of a single chlorine atom in the xenon environment is detected. Various XenCl2 cluster sizes have been investigated leading to the distinction between uncapped, half-capped and doubly capped structures
for these clusters. These structures have a profound influence on the photodissociation dynamics. Retrapping of one chlorine
atomic fragment and stabilization of the XeCl reaction product is only observed for the half and doubly capped clusters. The
experimental work is complemented by classical molecular dynamics calculations to get a full picture of the photodissociation.
Received: 17 February 1998 / Received in final form and Accepted: 28 July 1998 相似文献
19.
A. Nossov J. Pierre J. Beille V. Vassiliev B. Slobodin 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):467-472
The influence of hydrostatic pressure on the transport properties of (La1-xRx)0.67Ca0.33MnO3 (,Tb) ferromagnetic manganites is investigated. The enhancement of the Curie temperature TC under pressure agrees with previous data. In the paramagnetic range, the resistivity can be represented by a Mott localisation
law, with a characteristic temperature T0 decreasing with pressure. The variation of TC with pressure is compared to the effect induced by replacing La by a magnetic rare earth in (La1-xRx)0.67Sr0.33MnO3 manganites (, ..., Tm). The main effect is not related to the decrease of the mean radius of the cation, but to an additional scattering
by the magnetic moment of the rare earth.
Received: 15 May 1998 / Revised: 6 July 1998 / Accepted: 16 July 1998 相似文献
20.
C. Meneghini M. Maret V. Parasote M.C. Cadeville J.L. Hazemann R. Cortes S. Colonna 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):347-357
Polarized X-ray absorption fine structure (XAFS) measurements at the Co K and Pt L3 edges show that the perpendicular magnetic anisotropy found in epitaxial fcc CoPt3 (111) films stems from the existence of anisotropic local ordering. Such ordering, induced during the codeposition process
and dependent on the growth temperature, is characterized by preferential CoCo pairs in the film plane, balanced by preferential
CoPt pairs out of the plane, resulting from some Co 2D-segregation. Polarized XAFS at the Pt edge reveals similar anisotropic
local ordering in epitaxial hcp Co3Pt (0001) films exhibiting a larger magnetocrystalline anisotropy compared to that of bulk hcp Co. Besides, a polarization
dependence of the Co XANES profile is observed only for the Co3Pt films exhibiting hcp symmetry.
Received: 29 April 1998 / Revised: 27 July 1998 / Accepted: 31 August 1998 相似文献