共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
S.W.H. Eijt R. Currat J.E. Lorenzo P. Saint-Grégoire B. Hennion Y.M. Vysochanskii 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):169-178
The low frequency lattice dynamics and its relationship to the second order paraelectric-to-ferroelectric transition in Sn2P2S6 is studied. The dispersion branches of the acoustic and lowest lying optical phonons in the a*-c* plane have been obtained in the ferroelectric phase, for x-polarized phonons. Close to the phase transition a considerable softening is found for the lowest optical mode (Px), comparable to the behaviour observed in previous Raman investigations. As found previously in Sn2P2Se6, a strong coupling between the TO(Px) and TA(uxz) phonons is observed, although, apparently, not strong enough to lead to an incommensurate phase. The soft TO(Px) mode at the zone center is observed. The temperature dependence of its frequency and damping shows that the transition is
not entirely displacive. At low temperatures an unusual apparent negative LO-TO splitting is observed which is shown to arise
from the coupling of the x-polarized soft mode to the nearby z-polarized optical phonon. For comparison, the soft TO(Px) dispersion in the a*-b* plane is measured in both the paraelectric and ferroelectric phases. Consistent frequency changes and LO-TO splitting are
observed, revealing a significant interaction between the TA(uyx) and LA(uxx) acoustics branches and the TO and LO soft optic branches, respectively. In contrast, the nearby y-polarized optic branch shows almost no temperature dependence. Finally, the influence of piezoelectric effects on the limiting
acoustic slopes in the ferroelectric phase is discussed.
Received: 11 May 1998 / Revised and Accepted: 15 June 1998 相似文献
3.
P. Müller B.A. Bushaw W. Nörtershäuser K. Wendt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):33-44
Isotope shifts and hyperfine structure have been measured in 4snp 1 P1 and Rydberg states for all stable calcium isotopes and the radioisotope 41Ca using high-resolution laser spectroscopy. Triple-resonance excitation via
Rydberg state was followed by photoionization with a CO2 laser and mass selective ion detection. Isotope shifts for the even-mass isotopes have been analyzed to derive specific mass
shift and field shift factors. The apparent isotope shifts for 41Ca and 43Ca exhibit anomalous values that are n-dependent. This is interpreted in terms of hyperfine-induced fine-structure mixing, which becomes very pronounced when singlet-triplet
fine-structure splitting is comparable to the hyperfine interaction energy. Measurements of fine-structure splittings for
the predominant isotope 40Ca have been used as input parameters for theoretical calculation of the perturbed hyperfine structure. Results obtained by
diagonalizing the second-order hyperfine interaction matrices agree very well with experimentally observed spectra. These
measurements allow the evaluation of highly selective and sensitive methods for the detection of the rare 41Ca isotope.
Received 17 December 1999 and Received in final form 29 March 2000 相似文献
4.
A. Qayyum M.N. Akhtar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):181-184
Light emission during sputtering of graphite targets with 1–10 keV Ne+, Kr+ and Xe+ beams has been investigated in the 180-600 nm wavelength range. Beside the characteristic lines of sputtered C1 and C1
+, a continuum superimposed with a number of broad structures was observed in the 250-520 nm range, and having a maximum at
386 nm. Mass analysis of the sputtered flux confirmed the presence of negative carbon clusters C
m
-
, C2
- being the dominant one. Ion beam parameters i.e. ion mass, energy, current density and ion dose were varied to identify the origin of the continuum emission. On the basis
of the experimental results, it is suggested that the continuum is predominantly due to the overlapping of various band systems
of sputtered C2 with a small contribution from the heavier sputtered carbon clusters Cm (m>2).
Received 24 September 1999 and Received in final form 11 February 2000 相似文献
5.
E. Chappel M.D. Núñez-Regueiro F. Dupont G. Chouteau C. Darie A. Sulpice 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):609-614
Magnetisation measurements up to 23 T and submillimeter wave ESR in the frequency region 48-380 GHz have been performed on
NaNiO2 powders at low temperature. Also typical spectra above the Néel temperature are shown. At 4 K the magnetisation shows a spin-flop transition at 1.8 T and saturation at 10 T. /Ni confirms the low spin state of the Ni3+ ions. The susceptibility exhibits a maximum at K with and K. NaNiO2 is an A-type antiferromagnet: we derive K and K for the interactions between Ni ions within and between adjacent layers, respectively. The AFMR spectra yield an energy
gap of 52.5 GHz, in agreement with the spin-flop value derived from the magnetisation. The anisotropy of the g factor observed at 100 K with can be attributed to the Jahn-Teller effect for Ni3+ ions in the low spin state, which stabilises the occupation. We finally comment on the isomorphic controversial Li1-xNi1+xO2 compound.
Received 9 March 2000 and Received in final form 13 July 2000. 相似文献
6.
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
7.
Multi-wavelength excimer ultraviolet sources from a mixture of krypton and iodine in a dielectric barrier discharge 总被引:1,自引:0,他引:1
New ultraviolet (UV) sources (excimer lamps) have been demonstrated using mixtures of krypton and iodine in a high-pressure
dielectric barrier discharge to provide intense multi-wavelength radiation at λ=183 nm (atomic iodine line, 4
P
5/2?2
P
3/2), 191 nm (KrI*, B
1/2?X
1/2), 206 nm (atomic iodine line, 2
P
3/2?2
P
1/2), and 342 nm (I*
2, D
1/2?X
1/2). The characteristics of the optical emission spectra of the atomic species and the excited dimers (excimers) formed for
different total gas pressures and in the presence of a buffer gas have been investigated. The highest intensity, at 183 nm,
is obtained at pressures up to 1 bar while the overall emission spectra can be controlled by adjusting the total pressure.
The results show that these strong multi-wavelength lamps offer an interesting alternative to conventional UV sources.
Received: 1 March 2000 / Revised version: 5 April 2000 / Published online: 30 June 2000 相似文献
8.
E. Träbert H.-P. Garnir P.-D. Dumont T. Bastin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):25-31
Peculiar properties of ion-atom collision systems, in particular deviations from statistical populations of singlet and triplet
levels, can be studied by optical spectroscopy. We have extended earlier studies by VUV spectroscopy of a number of collision
systems at various collision energies in the 0.01-MeV/nucleon to 1-MeV/nucleon range, involving H2
+, H+, He+, He2+, Ne+, Ar+, and N2
+ as projectiles and Ne, Ar, and N2 as target gases. Statistically significant deviations of the relative intensities of singlet and triplet lines from simple
ratios are observed in the displaced terms of the valence shell of Ne III, corroborating and extending earlier work. For Ar
III, the energy dependences of singlet-to-triplet excitation ratios are very different for different projectiles. For N II,
in contrast, all observed line ratios are practically independent of the projectile energy.
Received 17 November 2000 and Received in final form 31 January 2001 相似文献
9.
B. F. Parsons K. E. Strecker D. W. Chandler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(1):15-20
In our previous work we investigated electronically non-adiabatic effects in
using crossed molecular beam scattering
coupled with velocity mapped ion imaging. The prior experiments placed
limits on the cross-section for electronically non-adiabatic spin-orbit
excitation
and electronically non-adiabatic spin-orbit
quenching
.
In the present work, we investigate
electronically non-adiabatic spin-orbit quenching for
which is the required first step for the
reaction of Cl* to produce ground state HCl+H products. In these
experiments we collide Cl (2P) with H2 at a series of fixed
collision energies using a crossed molecular beam machine with velocity
mapped ion imaging detection. Through an analysis of our ion images, we
determine the fraction of electronically adiabatic scattering in
Cl* +H2, which allows us to place limits on the cross-section for
electronically non-adiabatic scattering or quenching. We determine the following
quenching cross-sections σ quench(2.1 kcal/mol) = 26 ±
21 ?2, σ quench(4.0 kcal/mol) = 21 ±
49 ?2, and σ quench(5.6 kcal/mol) = 14 ±
41 ?2. 相似文献
10.
S. Kramp M. Doerr M. Rotter M. Loewenhaupt R. v.d. Kamp 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):559-563
The magnetic (H
,
T)-phase diagram of the orthorhombic compound NdCu2 was investigated for external magnetic fields up to 15 T parallel to the crystallographic c-direction. Magnetization and magnetostriction measurements reveal an anomalous change of the magnetic properties as well
as giant magnetostriction (GMS) and large hysteretic effects. This behaviour is similar to that observed in some other RCu2 compounds where it has been interpreted as a conversion of the magnetic Ising axis. In contrast to these other RCu2 compounds, however, the easy axis of magnetization in NdCu2 is the b-axis. The macroscopic measurements are compared with neutron diffraction experiments which reveal GMS along the b-axis and a new magnetic phase with propagation vector in the converted crystal.
Received 27 March 2000 and Received in final form 11 September 2000 相似文献
11.
Production, isolation, and characterization of group-2 metal-containing endohedral metallofullerenes
T. John S. Dennis H. Shinohara 《Applied Physics A: Materials Science & Processing》1998,66(3):243-247
80 , Ca/Sr/Ba@C82, Ca/Sr/Ba@C84) are investigated for the first time by UV-Vis-NIR absorption spectroscopy and high-resolution 13C NMR. Direct evidence of the endohedral nature and cage structures are revealed by these measurements. Furthermore, we have
found that each metallofullerene has 2–4 structural isomers, which have been isolated by multistage high-performance liquid
chromatography. These isomers have different cage structures and give characteristic UV-Vis-NIR absorption spectra.
Received: 22 September 1997/Accepted: 16 October 1997 相似文献
12.
A. Fioretti E. Arimondo A. Crubellier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(2):219-225
The measurements of fine-structure changing collisions in a cesium magneto-optical trap, reported in a previous work [A. Fioretti
et al., Phys. Rev. A 55, R3999 (1997)], are reanalyzed within a model based on the flux enhancement effect, which takes place in cold atomic collisions.
In the present analysis, we consider the cooperative effect of the long-range and the shorter-range excitation by the strong
trap laser. We evidence also the important role of the hyperfine structure of the Cs2 molecular levels asymptotically connected to the ground-state and excited-state dissociation limits.
Received 22 July 1999 and Received in final form 4 May 2000 相似文献
13.
A. Campana R. Cantelli F. Cordero M. Corti A. Rigamonti 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):49-54
Anelastic relaxation and 139LaNQR relaxation rates in La2–xSrxCuO4 for Sr content around 2 and 3 percent are discussed in terms of spin and lattice excitations and of the related ordering
processes. It is argued how the phase diagram of La2–xSrxCuO4 at the boundary between the antiferromagnetic (AF) and the spin-glass phase (x
= 0.02) could be more complicate than previously thought, with a transition to a quasi-long range ordered state at K, as indicated by neutron scattering data. On the other hand, the 139LaNQR spectra are compatible with a transition to an AF phase around K, in agreement with the phase diagram commonly accepted in literature. In this case the peaks in NQR and anelastic relaxation
rates around 150 K and 80 K respectively in La1.98Sr0.02CuO4, yield the first evidence of freezing process involving simultaneously lattice and spin excitations, possibly corresponding
to motion of charged stripes.
Received 18 May 2000 and Received in final form 11 July 2000 相似文献
14.
A. Johansen H. Saleur D. Sornette 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):551-555
Significant advances, both in the theoretical understanding of rupture processes in heterogeneous media and in the methodology
for characterizing critical behavior, allows us to reanalyze the evidence for criticality and especially log-periodicity in
the previously reported chemical anomalies that preceded the Kobe earthquake. The ion (Cl-, K+, Mg++, NO3
- and SO4
-) concentrations of ground-water issued from deep wells located near the epicenter of the 1995 Kobe earthquake are taken as
proxies for the cumulative damage preceding the earthquake. Using both a parametric and non-parametric analysis, the five
data sets are compared extensively to synthetic time series. The null-hypothesis that the patterns documented on these times
series result from noise decorating a simple power law is rejected with a very high confidence level.
Received 21 January 2000 相似文献
15.
The effect of an external electric field on the local layer structure is investigated in the SmC*
A, SmC*
FI and SmC* phases using X-ray diffraction. X-ray scattering and spontaneous polarization measurements are performed under several increasing
(and decreasing) steps of AC applied voltage. The effects of the electric field differ significantly from one phase to the
other. The chevron-to-bookshelf transition occurs abruptly at a high field value in the SmC*
A phase whereas layer deformations are more progressive and occur at lower field values in the other phases. Comparison of
the different behaviours suggests that the destruction of the chevron structure is mainly affected by the local molecular
order.
Received 16 July 2001 and Received in final form 7 December 2001 相似文献
16.
Yves Galerne 《The European physical journal. E, Soft matter》2000,3(4):355-368
We propose complements to the Renn model of the liquid crystal TGBC* phase. We argue that the rotation angle per helislab is spontaneously in the radian range, not too small to limit the energy
cost of the twist grain boundaries between the helislabs, not too large to preserve the double twisting efficiency. Taking
the elastic interactions between the helislabs into account, we show that the structure may undergo two different lock-ins,
provided that the uncontrolled interactions at the sample surfaces are small enough. First, for appropriate values of the
elastic constants, an angular lock-in may fix the rotation angle per helislab at values exactly commensurate to π. Three characteristic
lengths of the TGBC* phase, the TGB period and the thicknesses of both the smectic blocks and of the helislabs are then commensurate to one another,
with moreover, integer ratios at the most efficient commensurabilities. The TGBC* phase could thus exist in several versions, incommensurate and commensurate, according to the steps of a restricted Devil's
staircase. A second elastic lock-in should then arise in the commensurate TGBC* phases, to set the arrays of disclination lines between the helislabs in simple rectangular lattices, arranged in a helical
manner. Being placed right behind one another, the disclination lines then coincide when observed along the TGB axis. This
could explain the typical textures with square or hexagonal grids, observed in oriented samples. The commensurability of the
TGBC* phases could be analyzed with X-ray scattering experiments in the same manner as already reported for the TGBC phase.
Received 30 November 1999 and Received in final form 5 May 2000 相似文献
17.
R. Tenzer N. Grün W. Scheid 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):347-353
Total and differential cross-sections for the production of free electron-positron pairs are calculated for the reactions
Au79+ (10.8 GeV/u) on Cu29+, Ag47+ and Au79+. The methods used are the semiclassical approach and the solution of the time-dependent Dirac equation by a coupled channel
method with free wavepakets describing the created fermions. The obtained total cross-sections are in good agreement with
the experimental data. The differential cross-sections give informations about the correlation between the electron and positron.
Received 21 December 1999 and Received in final form 6 March 2000 相似文献
18.
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
19.
A.V. Belozerov M.L. Chelnokov V.I. Chepigin T.P. Drobina V.A. Gorshkov A.P. Kabachenko O.N. Malyshev I.M. Merkin Yu.Ts. Oganessian A.G. Popeko R.N. Sagaidak A.I. Svirikhin A.V. Yeremin G. Berek I. Brida Š. Šáro 《The European Physical Journal A - Hadrons and Nuclei》2003,16(4):447-456
Heavy-ion fusion reactions 48Ca + 204Pb and 44Ca + 208Pb leading to the same compound nucleus 252No* were run in attempts to produce new neutron-deficient spontaneous-fission isotopes of 249,250No using the electrostatic separator VASSILISSA. Production cross-sections for the spontaneous-fission activities with the
half-lives 5.6 and 54 μs observed in these reactions are compared with the measured ones for the well-known isotopes of 251 - 255No formed in the heavy-ion fusion reactions 48Ca + 206Pb and 48Ca + 208Pb. The obtained excitation functions for the reaction products formed after the evaporation of 1-4 neutrons from the corresponding
compound No nuclei have been compared with similar data obtained earlier and results of statistical model calculations.
Received: 26 July 2002 / Accepted: 5 November 2002 / Published online: 18 March 2003
RID="a"
ID="a"e-mail: eremin@sunvas.jinr.ru
Communicated by J. ?yst? 相似文献
20.
R. Koç H. Tütüncüler M. Koca 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(3):467-472
It is now well-known that electron (hole)-vibron coupling and hence Jahn-Teller (JT) effect is important understanding the
properties of C60 and related molecules. In this paper, we study H(2) coupling case to find the potential energy surfaces for the positively charged C60 molecule due to distortion. The H(2) Jahn-Teller system is of particular importance as this will be the JT effect displayed by C60 molecules removed with an electron. C60
+ is obtained by removing one electron from fivefold degenerate Hu highest occupied molecular orbital (HOMO) and a hole in HOMO interacts with the vibrational modes of C60 and symmetry is broken. We apply the method of symmetry breaking mechanism to obtain expressions for the potential energy
surface.
Received 27 December 1999 and Received in final form 15 May 2000 相似文献