共查询到20条相似文献,搜索用时 46 毫秒
1.
《Physics letters. A》2002,299(1):65-72
Coulomb–Born approximation has been used to study three different types of ionization in positronium (Ps) and hydrogen scattering. The present Ps–H system contains four centers; we have considered all the Coulomb interactions and neglected exchange assuming the fact that at relatively higher energies above thresholds, the effect of exchange is not so important. All the important target elastic and inelastic channels are included. The non-unitarity problem in the target elastic channels, discussed by McAlinden et al. in 1996 in their positronium–atom scattering studies is overcomed in the present calculation using the orthonormality properties of target wavefunctions and a simple algebra. Comparative studies are made among ionization cross sections with different target excitations and different Ps-excitations together with summed Ps-ionization, summed H-ionization, both-ionization, summed excitation, total ionization and total cross sections. The present Letter indicates the importance of all the three different types of ionization and the importance of target elastic channels in Ps–H scattering. 相似文献
2.
《Physics letters. A》1999,252(6):316-320
A thorough and systematic study has been performed for positronium (Ps) and helium (He) atom scattering using the first Born approximation. As a first step, the direct scattering has been studied. Here excitations of both the Ps atom and He atom, the ionization of the Ps atom with all the excitations of the He atom, the ionization of the He atom with all the excitations of the Ps atom and the ionizations of both the Ps and He atoms are taken into consideration. For the different states of the He atom, the wavefunctions suggested by Winter and Lin [Phys. Rev. A 12 (1975) 434] are used. For the ionization channels the continuum Coulomb wavefunctions have been taken for the ionized electrons. 相似文献
3.
The atomic ionization processes induced by scattering of neutrinos play key roles in the experimental searches for a neutrino
magnetic moment. Current experiments with reactor (anti)neutrinos employ germanium detectors having energy threshold comparable
to typical binding energies of atomic electrons, which fact must be taken into account in the interpretation of the data.
Our theoretical analysis shows that the so-called stepping approximation to the neutrino-impact ionization is well applicable
for the lowest bound Coulomb states, and it becomes exact in the semiclassical limit. Numerical evidence is presented using
the Thomas-Fermi model for the germanium atom. 相似文献
4.
In strong-field double ionization,two electrons are ionized by intense laser field.These two electrons move in the laser field and the state is described by a Coulomb-Volkov state,where the repulsive Coulomb state describes the relative motion of the two electrons and the Volkov state describes the center-of-mass motion of the two electrons in the laser field.In the frame of scattering theory,we derive a simple analytical formula of the double ionization of He-like atoms.The effect of the Coulomb force between two electrons on the double ionization process is discussed.Numerical studies disclose that the Coulomb force enhances the ionization rate of high-energy electrons but suppresses the ionization rate of the lowest-energy electrons. 相似文献
5.
The differential and total cross sections are calculated for the ionization of helium-like ions that is accompanied by the excitation of residual ions to ns states owing to an electron impact. Nonrelativistic perturbation theory in electron–electron interaction with Coulomb functions used for a zero-order approximation underlies these calculations. The expressions obtained in this way have a universal character. They are applicable at moderate values of the target charge number Z and high energies of incident electrons. A comparison with total cross sections calculated for the helium atom within various theoretical approaches is performed. 相似文献
6.
Scattering solutions of the second-order Dirac equation for the case of the Coulomb potential and which are correct to first order in the coupling constantZe 2/hc are investigated and found to describe pure Coulomb scattering equally well as the Sommerfeld-Maue wave functions. Errors introduced by the use of these solutions are studied in a numerical calculation of cross sections for nuclear electric-quadrupole excitation by high-energy electrons. The use of these wave functions is suggested for simplified calculations of lowest-order Coulomb corrections to Born approximation results for various electron-nucleus processes. 相似文献
7.
Alpha particle and deuteron impactL-subshell ionization cross-sections of Ar, Cu, Ge, Br, Zr and Ag have been computed using Vriens’ expressions for ionization
cross-section of atoms due to impact of heavy charged particles. The effects of Coulomb deflection of the projectile and increase
in binding of the target electron in the presence of projectile have been incorporated. Hartree-Fock velocity distributions
for the target electrons have been used in the present calculations. The simple binary encounter approximation model is found
to give results which are in satisfactory agreement with those obtained from experiments and from other theories. 相似文献
8.
We explore the complete breakup of the Li atom after absorption of a single photon, the purest example of the so-called four-body Coulomb problem. The resulting strongly correlated three-electron continuum is investigated by calculating the angular distributions of the ionized electrons using advanced close-coupling techniques. We find that the distributions are dominated by the Coulomb interactions between the electrons, that multiple break-up processes can be identified, and that the complex dynamics of the fragmentation process are evident for most scattering geometries. 相似文献
9.
We explore the excitation of water molecules subject to short and intense laser pulses in the frame of time-dependent density function theory (TDDFT) at the level of the time-dependent local-density approximation (TDLDA), applied to valence electrons, coupled non-adiabatically to molecular dynamics (MD) of ions. We first study the optical absorption spectra of the water molecule as an observable in the "linear" domain and results are in good agreement with experiments. We then explore the influence of the laser frequency on the excitation. It is found that when the laser frequency is off-resonant or highly above the resonant region, the excitations are weak whereas for the resonant frequency case, the ionization is enhanced and bond lengths are enlarged. Furthermore, a direct coupling of ions with the laser pulse with the off-resonant frequency is found when investigating the OH bond lengths. We finally study the effect of laser intensity on the excitation of H 2 O and it is found that ionization increases when the laser intensity varies from low to high and we observe stable vibrations to Coulomb fragmentation when the ionization is up to typically two more charge units. 相似文献
10.
To improve the Coulomb-Born approximation (CBA) theory of ionization in positronium (Ps) and atom scattering, the effect of
exchange is introduced. The nine-dimensional exchange amplitude for ionization of Ps in Ps—H scattering is reduced to a two-dimensional
integral using the present Coulomb-Born-Oppenheimer approximation (CBOA). The methodology is extremely useful to evaluate
ionization parameters for different target systems and for different types of ionization processes. It is then applied to
evaluate the Ps-ionization cross-section and to estimate the effect of exchange on Psionization in Ps-H system. We establish
the importance of exchange at lower energy region. 相似文献
11.
A. I. Mikhailov I. A. Mikhailov 《Journal of Experimental and Theoretical Physics》1999,89(6):1023-1029
Double ionization and excitation ionization in Compton scattering for heliumlike ions in metastable states are investigated.
The electron energy distribution for double ionization and the total cross sections for both processes are calculated. The
calculations are carried out in the zeroth order of perturbation theory with respect to electron-electron interaction, using
Coulomb wave functions as the first approximation. The resulting equations are valid only in the high-energy nonrelativistic
range. It is assumed that Z≫1, but αZ≪1 (Z is the charge of the nucleus, and α is the fine-structure constant).
Zh. éksp. Teor. Fiz. 116, 1889–1902 (December 1999) 相似文献
12.
V. D. Kagan 《Physics of the Solid State》2005,47(2):217-224
Inelastic electron-phonon scattering in which the electron is captured or escapes from the Coulomb field of an impurity is taken into account in the kinetic equation for conduction electrons. This scattering is shown to become strong in a certain energy range. In this range, the distribution functions of free and bound electrons are correlated in such a way that there is a balance between the trapping and ionization processes. The existence of a region of strong scattering is the decisive factor in calculating the experimentally measurable trapping and ionization coefficients, which enter into the electron balance equation. 相似文献
13.
A. Yu. Elizarov I. I. Tupitsyn 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(1):67-74
The plane wave Born approximation is used to calculate total
electron impact ionization cross section of silver and copper.
Wavefunctions of the target and residual ions were modeled by non orthogonal
Hartree-Fock and Dirac-Fock orbitals. The wave
functions of the atom and residual ion
are calculated with allowance for relaxation effects.
The one-electron wavefunction of the continuous spectrum for the ejected
electron is obtained using single-configuration Hartree-Fock and
Dirac-Fock method. The orthogonalization of the ejected electron wave
functions to all occupied orbitals of the target atom is performed.
Results of calculations are compared to available experimental measurements
and theoretical calculations performed by non relativistic one-electron
PWBA, where the ejected electrons is modeled by the hydrogenic Coulomb
wave function. 相似文献
14.
入射电子被中性原子散射过程中的库仑波描述 总被引:1,自引:0,他引:1
在前期工作的基础上,给出了有效电荷Zeff的解析形式.研究发现:有效电荷Zeff与入射电子的能量和散射角有关.我们早期工作的一个重要缺陷是:对于初、末通道,分别使用了解析的平面波和库仑波,而现有的波函数与早期工作之间的一个重要差别在于:在初通道,现有的波函数包含有入射电子与中性原子之间的短程相互作用效应,而早期文章则没有这种效应.这里使用的末态波函数与以前是相同的.当入射电子处在有效电荷库仑场的情形下,我们计算了电子入射离化氦原子的三重微分截面,并发现现有的理论计算与实验结果很好的一致. 相似文献
15.
16.
利用修正的BBK理论,考虑入射道的库仑相互作用及出射道电子的交换对称性,在共面-等能分享-垂直角度碰撞几何中,计算了能量分别为85.6、105.6、227.6和375.6eV的入射电子碰撞Li+(ls)电离的三重微分截面.讨论了干涉效应、关联效应及入射道库仑场对截面的影响.Based on revised BBK theory, triple differential cross sections (TDCS) have been calculated for ionization of Li + (ls) by electron impact. A coplaner, equal energy, fixed re1ative angle kinematics are chosen and the particular case where the scattered and ionized electrons emerge perpendicular to each other is emphasized. The incoming electron state is considered by a Coulomb wave from the long range... 相似文献
17.
Fischer D Moshammer R Dorn A Crespo López-Urrutia JR Feuerstein B Höhr C Schröter CD Hagmann S Kollmus H Mann R Bapat B Ullrich J 《Physical review letters》2003,90(24):243201
Double ionization of helium by 6 MeV proton impact has been explored in a kinematically complete experiment using a "reaction microscope." For the first time, fully differential cross sections for positively charged projectiles have been obtained and compared with data from 2 keV electron impact. The significant differences observed in the angular distribution of the ejected electrons are attributed to the charge sign of the projectile, resulting in different dynamics of the four-particle Coulomb system, which is not considered in the first Born approximation. 相似文献
18.
C. Cornaggia 《Laser Physics》2009,19(8):1660-1670
Multiple ionization of small molecules leads to multifragmentation called Coulomb explosion. The atomic positions prior to the fragmentation event are determined from the multicharged fragments trajectories. Following the pioneering contribution of Prof. N.B. Delone on atomic ionization using strong laser fields, intense femtosecond laser pulses in the 1015 W cm?2 range permit an efficient removal of valence electrons. Pulse durations have to be reduced to a few cycles in order to avoid any significant molecular stretching during multiple ionization. Pumpprobe excitation schemes offer promising perspectives for straightforward ultrafast Coulomb explosion imaging of excited and ionized molecular species. 相似文献
19.
V. V. Serov V. L. Derbov T. A. Sergeeva S. I. Vinitskii 《Physics of Particles and Nuclei》2013,44(4):757-790
A number of recently developed methods for calculating multifold differential cross sections for photoionization and electron impact ionization of atoms and molecules with two active electrons are reviewed. The methods are based on unique approaches to the calculation of three-body Coulomb wave functions. The exterior scaling method and the driven Schrödinger equation formalism are considered. The effectiveness of the time-dependent approaches to the scattering problem, such as the paraxial approximation and the time-dependent scaling, is demonstrated. A novel numerical method is formulated, which has been developed by the authors to solve the six-dimensional Schrödinger equation for an atom with two active electrons on the basis of the Chang-Fano transformation and the discrete variable representation. The threshold behavior manifested by the angular distributions of the two-electron photoionization of a negative hydrogen ion and a helium atom and the multifold differential cross sections for the electronimpact ionization of hydrogen and nitrogen molecules are analyzed on the basis of numerical simulations. The Wannier law for the angular distribution of double ionization is demonstrated to be incorrect even at very low energies. 相似文献
20.
In this paper the processes of excitation and ionization inside the cathode of a hollow cathode are discharge will be studied. The electron energy distribution function is calculated from the kinetic equation. For this we take into account the following processes: elastic and inelastic collisions of electrons with atoms, Coulomb interaction between emitted fast electrons and electrons of the plasma. 相似文献