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1.
A model of electron detachment from negative ions is based on the approximation of instantaneous perturbation. A simple analytical representation for the ground state of the weakly bound electron is chosen to reproduce the radial distribution of electron density at any distance from the center of the ion. The probabilities of electron detachment from negative hydrogen and lithium ions are derived as functions of the transferred momentum of the laser field. The contribution of the inner shells of ions to the electron detachment is estimated. The momentum distribution of electrons in the final state is obtained. The effect of a pulse train on the total probability of detachment is considered for different pulse polarities. The conditions for the partial electron return to the initial state are revealed. 相似文献
2.
C. Blondel C. Delsart F. Dulieu C. Valli 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):207-216
Photodetachment of ions is performed in the presence of a static electric field. A high spatial resolution electron detector is used to map
out the ejected electron's wave function. Propagation over half a metre does not alter the stationary structure the electron
wave possesses in the direction orthogonal to the detachment motion. Nodes and antinodes of electron current density are observed,
that can be interpreted as direct imaging of the internal atomic wave function. Because detachment of a negative ion can be
represented accurately in the free-electron approximation, the obtained images can also be viewed as direct experimental representations
of the Green function of the uniform acceleration problem. Agreement of the measured distributions with the exact expression
of this wave-function appears quite satisfactory.
Received: 5 June 1998 / Accepted: 16 October 1998 相似文献
3.
L. Lammich S. Altevogt H. Buhr H. Kreckel S. Krohn M. Lange D. Strasser R. Repnow M. Grieser R. Schinke Z.-W. Qu H. Zhu D. Schwalm D. Zajfman A. Wolf 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):103-111
The fragmentation of LiH2
- anions after electron
impact was investigated at the heavy-ion storage ring TSR.
The main reaction channel was found to be electron detachment followed by a
breakup into LiH + H.
In the first ms after production of the molecular ions in a cesium
sputtering ion source, additional
contributions were observed in the Li + H2 and Li- + H2 channels,
hinting at an initial population of a short-lived state of the anion.
To gain a better understanding of the mechanisms underlying the observed
behavior of the system, ab initio calculations of relevant potential
energy surfaces were performed at selected geometries.
The experimental findings are discussed in the
light of these calculations. 相似文献
4.
对超短超强激光脉冲在大气中传播时形成的电离通道的寿命进行了理论研究.综合考虑了通道中自由电子,正离子,负离子的复合,自由电子和中性分子的吸附以及在后续 激光作用下的退吸附过程.推导出了退吸附激光强度恒定时通道中带电离子密度的速率方程 的解析解.计算结果表明,通过引入退吸附激光抑制电子和中性分子的吸附作用能够在微秒 的时间尺度上将电子密度维持在1012—1013cm-3的水平,在相同的波长 和平均功率下,短脉冲序列的退吸附效果要略好于连续激光
关键词:
等离子体通道
复合
吸附
退吸附
寿命 相似文献
5.
Z. Lj. Petrović J. V. Jovanović V. Stojanović Z. M. Raspopović Z. Ristivojević 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(1):87-94
We have used a simple semi-analytic — momentum transfer theory (MTT)
to develop negative halogen ions/noble gases momentum transfer
integral cross sections based on the available data for reduced
mobility at 300 K as a function of E/N. The unfolded cross
sections were validated or further improved by assuring a good agreement between our Monte
Carlo (MC) calculated transport data and the available
experimental results. The data are produced with an aim to provide plasma modellers with cross section data and transport
coefficients. We have also calculated the net
rates of elastic scattering and detachment. 相似文献
6.
C. Herwig J.A. Becker 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):51-54
The growth of small tellurium clusters in helium and the influence of a metal impurity (dysprosium atoms) on the cluster size
distribution are investigated in a double laser vaporization source. A model describing the role of the carrier gas as collision
partner is presented, emphasizing the crucial influence of the gas pressure on cluster formation. Changes in cluster reactivity
due to dysprosium addition are discussed in terms of ionic structures Dy
3 +(Te
N)3 - containing a radical electron.
Received 28 November 2000 相似文献
7.
M. Block O. Rehm P. Seibert G. Werth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):461-465
We have measured the lifetime of the metastable 3D
5/2
level in Ca+ using the “quantum jump" technique on a single stored and laser cooled ion in a linear Paul trap. We found a linear dependence
of the measured decay rate on the power of the laser which repumps the ions from the long lived 3D
3/2
level. This can be explained by off-resonant depletion of the 3D
5/2
level. The proper lifetime of this level is obtained by a linear extrapolation of the measured lifetime to zero laser power.
We obtain 1100(18) ms in agreement with theoretical calculations. The observed systematic change of the decay rate resolves
discrepancies between earlier experiments in which this effect had not been considered. Measurements on a linear chain of
10 laser cooled ions showed unexpected frequent coincidences of quantum jumps within our observation time of 20 ms. This indicates
a so far unexplained correlation between the ions in the chain at large distances.
Received 3 March 1999 相似文献
8.
报道了放电引发的非链式HF(DF)激光器中的激活介质由电子碰撞负离子分离引起的电离非稳定性。这种非稳性出现在电极空间分离、脉冲CO2激光加热的基于sF6的混合气体的大体积放电中。实验研究了自引发体放电过程中由激光加热引起的放电等离子体的自组织现象以及由此在放电间隙的大部分区域形成的准周期等离子体结构。重点分析了等离子体结构随气体温度和注入能量的变化,讨论了等离子体自组织对电子碰撞分离不稳定性所产生的影响,解释了混合气体中由于电子碰撞使负离子消失导致的单等离子体通道移动的产生机理。 相似文献
9.
G. Bilalbegović 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):43-49
The first 52 fs of a time evolution of the electron density in OCS after an interaction with an intense sub 10 fs laser pulse
are studied using the time-dependent density functional theory. The nuclear motion in this linear trimer is simulated by the
classical molecular dynamics method. Laser fields of intensity 1013 W/cm2 and 1015 W/cm2 are used. Details of the laser induced changes of the structure, as well as the ionization rate are sensitive to the applied
field intensity and its polarization. It is found that under suitable conditions the OCS molecule bends soon after an interaction
with a laser pulse. A deviation from the linear geometry of up to 23.6° and charged ions of up to +3 are observed. The time
evolution of electric dipole moments and the time-dependent electron localization function (ELF) are also studied. 相似文献
10.
T. Döppner Th. Diederich J. Tiggesbäumker K.-H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):13-16
Magnesium clusters grown in helium droplets and ionized with femtosecond laser pulses have been studied by high resolution
mass spectrometry. For moderate laser intensities the abundance spectra show characteristic features indicating electronic
shell effects. Compared to clusters of s1-electron metals additional shell closures appear resulting from an electron rearrangement. Irradiation with higher laser
intensities leads to a decomposition of the magnesium clusters into atomic ions. Due to charge exchange with the surrounding
helium matrix mainly singly and doubly charged magnesium ions remain. In addition, the occurrence of MgHeN
+-complexes is observed. Their abundance depends on the shape of the laser field, i.e. the laser width and the optical delay when applying the pump-probe technique.
Received 2 January 2001 相似文献
11.
Single electron detachment cross section for 10-40keV Si^- and Ge^- in collisions with Ar are measured and compared with other available experimental results. In our experimental energy region, the trend of cross sections is almost constant. The cross sections of Ge larger than Si can be understood by including electron affinity and size of negative ions. 相似文献
12.
W. Cui Y. Hu C. Lifshitz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):565-571
A new instrument has been constructed whose purpose is to study time-resolved photodissociation (TRPD) of small peptide ions.
Laser desorption of neutral peptides is combined with laser photoionization in an ion trap followed by thermalization, laser
photodissociation and time of flight mass analysis. Ionization and excitation take place through an aromatic chromophore at
the C-terminus of the peptide whereas dissociation produces the immonium ion at the N-terminus. The long-range purpose is
to uncover the role of IVR in unimolecular fragmentations of peptide radical cations. One avenue is the determination of microcanonical
rate constants at a well-defined internal energy E for a series of peptides possessing the same chromophore, undergoing the same fragmentation but having a variable number
of degrees of freedom. This paper demonstrates the feasibility of the method and provides the first attempts at rate measurements
for the peptide leucyl tyrosine (LeuTyr).
Received 6 January 2002 Published online 13 September 2002 相似文献
13.
J. T. Dickinson 《Applied Physics A: Materials Science & Processing》2008,92(4):1025-1030
Below laser fluences where a plasma is formed (the so-called plasma or plume formation threshold) a number of fundamental
phenomena can occur where particles such as atomic and molecular ions, atoms and molecular neutrals, and electrons can be
emitted. An understanding of such processes is necessary to develop predictive models for material removal from laser irradiated
surfaces—at the foundation of laser etching, machining, and pulsed laser deposition. We have reported on a number of the mechanisms
for such emission processes. Here, due to space limitations, we present a summary of our studies on the formation of negative
alkali ions from single crystal KCl during exposure to pulsed 248-nm radiation at fluences well below the threshold for plasma
formation. Despite the high electron affinities of the corresponding halogen atoms, negative halogen ions were not detected.
Significantly, the positive and negative alkali ion distributions overlap strongly in time and space, consistent with K formation
by the sequential attachment of two electrons to K+. Negative alkali ions are also observed under comparable conditions from LiF, NaCl, and KBr. In each material, the strong
overlap between the positive and negative alkali ion distributions, and the lack of detected negative halogen ions, suggest
that negative ion formation involves a similar mechanism. 相似文献
14.
A systematic theoretical study of laser-irradiated targets made of material with increasing atomic number has been performed.
The formation of energetic light ions resulting from the interaction of an intense ultrashort pulse laser with thin planar
targets is investigated theoretically with a two-dimensional relativistic electromagnetic particle-in-cell model. A common
parameter, the areal electron density of the foil, can be used to describe qualitatively targets made of different material.
By varying either the laser intensity or the target thickness we observe a gradual transition of various ion acceleration
mechanisms from one into another. Light ions, such as H+, Li3+, C6+, and Al13+, can be accelerated to GeV energies with existing laser systems at a laser fluence of 10–20 J/μm2. 相似文献
15.
S. Ali P. K. Shukla 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):319-324
By using a quantum hydrodynamic (QHD) model, we derive a generalized
dielectric constant for an unmagnetized quantum dusty
plasma
composed of
electrons, ions, and charged dust particulates. Neglecting the electron
inertial force in comparison with the electron pressure, and the force
associated with the electron correlations at a quantum scale, we discuss two
classes of electrostatic instabilities that are produced by streaming ions,
and dust grains. The effects of the plasma streaming speeds, the thermal
speed of electrons, and the quantum parameter are examined on the growth
rates. The relevance of our investigation to dense astrophysical plasmas is
discussed. 相似文献
16.
A mathematical model describing the discharge kinetics and lasing characteristics of copper bromide vapor laser with neon and hydrogen additives has been developed. The suggested model is based on a “zero-dimensional” model and offers simple mechanisms to explain discharge kinetics mechanisms, different physical processes and hydrogen additive effects on the copper bromide vapor laser.The model estimates the temporal evolution of discharge voltage and current, population densities, laser beam density, electron temperature and radial distribution of pressure and buffer gas temperature. The suggested mechanism assumes that the electron detachment from negative hydrogen ions does not contribute to the copper ionization process.Numerical solutions of a nonlinear rate equation system predict the generation of nanosecond pulses. The calculated maximum values of discharge voltage, current, average output laser power, electron temperature, etc. are in good agreement with other reported calculated and experimental data. 相似文献
17.
Absolute net nuclear polarizations and their time and concentration dependences are reported for the products of laser pulse initiated electron transfer from naphthalene and naphthalene derivatives to 1,2-dicyanoethenes. They represent different prototype cases for radical ion pair formation and decay pathways and are used to test predictions from the highfield radical pair theory of CIDNP. By quantitative analyses reaction efficiencies, rate constants for degenerate electron exchange and nuclear relaxation times of the radical ions are obtained. 相似文献
18.
M. Kubkowska P. Gasior M. Rosinski J. Wolowski M. J. Sadowski K. Malinowski E. Skladnik-Sadowska 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):463-466
This paper describes results of spectroscopic investigation of laser-produced tungsten plasma. The laser intensity on the
target surface reached up to 30 GW/cm2 depending on the focusing conditions. Optical spectra emitted from plasma plumes which were formed under vacuum conditions
in front of the tungsten target due to the interaction of Nd-YAG laser pulses (1.06 μm, 0.5 J), were characterised by means
of an optical spectrometer (λ/Δλ= 900) in the wavelength range from 300 to 1100 nm. The spectra were recorded automatically
with the use of a CCD detector with exposition time varied from 100 ns to 50 ms. On the basis of WI and WII lines it was possible
to estimate electron temperature and electron density which corresponded to the expansion phase of the plasma. Te and Ne were measured as 1.1 eV and 8×1016 cm-3, respectively. The spectra collected by the ion energy analyser showed that the plasma included tungsten ions up to 6+ ion
charge. Signals from the ion collector allowed to estimate the average value of ion energy of tungsten as 4.6 keV. Basing
on this value the electron temperature corresponding to the initial stage of the plasma formation was estimated to be about
320 eV. Optical microscope investigation showed that laser irradiation caused structural changes on the surface of the target. 相似文献
19.
We study partial detachment rate and photodetachment asymmetry of F− detached by half-cycle linearly polarized laser field using numerical simulation. Similar to photodetachment for negative ions in few-cycle laser fields, we find that partial detachment rates of a couple opposite directions in the above-threshold detachment of F− are not equal, the detachment is asymmetric. Furthermore, the photodetachment asymmetry degree increases with carrier-envelop phase (CEP) as the peak laser intensity becoming stronger or the pulse width becoming shorter. The maximal asymmetry degree is stronger with higher laser intensity. We confirm the effect of the CEP, laser intensity and pulse width on the above-threshold detachment of F− in half-cycle laser fields. It provides a possible way to determine the CEP of half-cycle laser fields by measuring detached photoelectrons. 相似文献
20.
M. Sewtz M. Laatiaoui K. Schmid D. Habs 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(1):139-145
The element specific electron configuration of ions directly reflects the two quantum mechanical observables 〈r2〉 and rmax, which denote the r2 expectation value of the electron density and the principle maximum of the wave function of the outermost electron orbital,
respectively. Thus, the determination of these observables may present a new access to element identification of single superheavy
nuclides. In this paper, we discuss how these observables are related to ionic radii deduced from ion-mobility data using
the most simple hard sphere model and
semi-empirical (n,6,4) model potentials for the interaction of heavy ions with noble gases.
A concept for a high resolution ion-mobility spectrometer is presented. Optimum extraction efficiency of the ions will be
achieved by decoupling the ion motion from the electric field drift by the friction force of the suitably shaped gas flow
at the exit nozzle. 相似文献