共面双对称条件下电子碰撞Ar原子单电离的一阶扭曲波Born近似

在共面双对称几何条件下,利用一阶扭曲波Born近似计算了中低能电子碰撞Ar原子(3p壳层电子)单电离的三重微分截面,并与最近的实验数据做了比较.结果表明,对于Ar原子,当入射电子能量比电离阈高40 eV以上,随着入射能量的增加,binary和recoil碰撞机理逐渐占据支配地位;在近阈能量范围,上述碰撞机理不再处于支配地位,扭曲效应明显.要完备地描述中低能入射条件下Ar原子的电子碰撞电离过程,理论模型必须同时考虑多种散射机理.     

Inner-shell ionization of atoms by electron,positron and photon impacts

Plane wave Born approximation with Coulomb, relativistic and exchange corrections is employed to obtain L1-, L2- and L3-subshell ionization cross sections of several atoms due to electron and positron impacts for projectile energy varying from the threshold of ionization to 60 times the threshold energy. Photoionization cross sections for all the three L-subshells of the atoms are also calculated using the hydrogenic approximation for the atomic wave functions. For L3-subshell the present cross sections due to electron impact are in good agreement with a number of experimental data for different atoms over the entire energy range investigated. For L1- and L2-subshells the present calculations yield qualitative agreement with the experimental data. The agreement between the present results and the limited experimental data for positron impact is also satisfactory. The hydrogenic approximation for the L-subshell photoionization is found to be good at small photon energies but it underestimates the cross sections at large photon energies.     

Ultrafast electronuclear dynamics of H(2) double ionization

The ultrafast electronic and nuclear dynamics of H(2) laser-induced double ionization is studied using a time-dependent wave packet approach that goes beyond the fixed nuclei approximation. The double ionization pathways are analyzed by following the evolution of the total wave function during and after the pulse. The rescattering of the first ionized electron produces a coherent superposition of excited molecular states which presents a pronounced transient H(+)H(-) character. This attosecond excitation is followed by field-induced double ionization and by the formation of short-lived autoionizing states which decay via double ionization. These two double ionization mechanisms may be identified by their signatures imprinted in the kinetic-energy distribution of the ejected protons.     

Dynamics of electronic and nuclear motion in a molecular hydrogen ion in a strong laser field

The dynamics of the electron and ion subsystems of a molecular hydrogen ion in the field of femtosecond titanium-sapphire laser radiation is investigated by using numerical simulation. The dependence of the probability of ionization and excitation of various electron states of H ₂ ⁺ on the radiation intensity and on the orientation of the molecule axis relative to the direction of polarization of the electric field of the wave is investigated. It is shown that the population of all electronic states of the molecule (except the ground state and the first excited state) is negligibly low in a wide range of radiation intensity. In such a situation, if the probability of system ionization is also low, the dynamics of vibration-rotation motion of nuclei in the molecule can be considered in the approximation of two potential surfaces (energy levels). The possibility of the effective orientation of the molecular axis along the direction of the electric field of the wave in the absence of dissociation of the system is considered.     

电子氢原子碰撞电离能量微分截面和总截面的理论计算

利用扭曲波玻恩交换（ＤＷＢＥ）近似方法对电子－氢原子碰撞电离截面进行了计算，计算所得总截面和能量微分截面均与最新的实验结果进行了比较，比较结果显示本计算与实验有较好的符合。还给出了能量微分截面的高斯拟合公式，文中对实验与理论计算存在的一些差距进行了讨论。 关键词：     

Ionization of the water by intense ultrashort half-cycle electric pulses

The ionization of the water molecule by intense ultrashort half-cycle electric pulses is studied theoretically. The formation of the electron wave packets in the continuum was investigated by calculating ionization probability densities using classical and quantum mechanical models. Single active electron and frozen core calculations were performed within the hydrogenic approximation. Electrons from the highest occupied molecular orbital 1b₁1b_1 were considered. We found good agreement between the classical and quantum mechanical calculation at high intensities, where the over-the-barrier ionization mechanism is dominant.     

Excitation-autoionization cross-sections and rate coefficients for Ge-like ions

Results of cross-section and rate coefficient calculations for electron impact direct and indirect ionization of ions belonging to the GeI isoelectronic sequence (ground 3d104s24p2) are presented. The cross-sections are given at near threshold energies for the five ions Kr4+, Mo10+, Xe22+, Pr27+ and Dy34+. The rate coefficients are computed for all the ions from Kr4+ to U60+ in the GeI sequence at seven electron temperatures (kTe = 0.1EI, 0.3EI, 0.5EI, 0.7EI, EI, 2EI and 10EI, where EI is the first ionization energy). The calculations include the contribution of direct ionization (DI) calculated with the Lotz formula approximation and the contributions of excitation-autoionization (EA) calculated in the framework of the distorted wave (DW) approximation for the 4s-nl, 3d-nl and 3p-nl resonant inner-shell excitations. The ionization enhancement due to the EA channels is shown as a function of Z along the GeI isoelectronic sequence.     

Theoretical study of the ionization of orbital-polarized p-excited alkali atoms by electron impact. 3D representation of the results

The Born-Coulomb approximation was used to study the electron impact ionization of p-excited Li and Na atoms with a given projection m of the orbital angular momentum on a specified axis. The wave function of the initial state of the atom electron was calculated using the effective charge approximation. The transformation of the initial wave function upon rotation of the coordinate system was considered. An analytical expression for the ionization amplitude was derived. Numerical results for the angular distributions of double differential cross sections of ionization were represented in the form of three-dimensional images.     

共面双对称几何条件下Ne原子(e,2e)反应的三重微分截面

利用标准一阶扭曲波玻恩近似方法（DWBA）计算了共面双对称几何条件下不同能量电子碰撞电离Ne原子的三重微分截面(TDCS),与Nixon和Murray 最新的实验测量数据进行比较.当入射电子能量较低时,理论计算结果和实验数据符合较差;随着入射电子能量的增加,而符合程度逐渐改善.     

共面双对称几何条件下Ne原子(e,2e)反应的三重微分截面

利用标准一阶扭曲波玻恩近似方法(DWBA)计算了共面双对称几何条件下不同能量电子碰撞电离Ne原子的三重微分截面(TDCS),与Nixon和Murray[1]最新的实验测量数据进行比较.当入射电子能量较低时,理论计算结果和实验数据符合较差;而随着入射电子能量的增加,符合程度逐渐改善.     

Plane wave born cross sections including exchange forK-shell ionization of light atoms

Cross sections forK-shell ionization by electron impact have been calculated in plane wave Born approximation (PWBA) including outer screening with allowance for electron exchange in Ochkur approximation. The results agree reasonably with available experimental data.     

Molecular above-threshold ionization with a circularly polarized laser field

Molecular above-threshold ionization by a circularly polarized laser field is investigated. Our theoretical approach is based on the modified molecular strong-field approximation. Various gauge-dependent versions of this approximation are considered and homonuclear and heteronuclear molecular species characterized by different symmetries are used as targets. As in the case of a linearly polarized field, the imprint of the molecular multicenter structure can be observed in the above-threshold ionization spectra. It manifests itself as minima in the rate of the ionized electrons as a function of their energy. The locations of these minima are strongly influenced by the symmetry of the corresponding highest occupied molecular orbital as well as the internuclear separation. Analyzing the interference structures of the electron spectra one can obtain information about the molecular symmetry.     

Multiphoton ionization of the hydrogen atom by a circularly polarized electromagnetic field

This paper examines the multiphoton ionization of the ground state of the hydrogen atom in the field of a circularly polarized intense electromagnetic wave. To describe the states of photoelectrons, quasiclassical wave functions are introduced that partially allow for the effect of an intense electromagnetic wave and that of the Coulomb potential. Expressions are derived for the angular and energy distributions of photoelectrons with energies much lower than the ionization potential of an unperturbed atom. It is found that, due to allowance for the Coulomb potential in the wave function of the final electron states, the transition probability near the ionization threshold tends to a finite value. In addition, the well-known selection rules for multiphoton transitions in a circularly polarized electromagnetic field are derived in a natural way. Finally, the results are compared with those obtained in the Keldysh-Faisal-Reiss approximation. Zh. éksp. Teor. Fiz. 116, 807–820 (September 1999)     

The effect of wave function orthogonality on the simultaneous ionization and excitation of helium

Within the framework of the first-order Born approximation, the triple differential cross sections （TDCSs） for simultaneous ionization and excitation of helium are calculated. The wave function of the ejected electron is chosen to be orthogonal or non-orthogonal to the wave function of the bound electron before ionization. It is found that the orthogonality has a strong effect on the TDCS, especially when plane waves and Coulomb waves are used to describe the projectile and the ejected electron.     

L-shell ionization in proton-atom collisions

The cross section of ionization of atoms by protons is calculated in the plane-wave approximation. It is shown that the wave function of the ejected electron must be orthogonal to all wave functions of the atom. A method taking into account a finite number of wave functions in the calculation of the ionization amplitude is proposed. The calculated cross sections of ionization of nitrogen, oxygen, and neon atoms by protons agree well with the experimental data and results of calculations carried out by other authors.     

Calculation of the cross section of helium ionization by an electron impact with the formation of a helium ion in an excited state

The total cross sections of He and He⁺ ionization by an electron impact are calculated in the first Born approximation. Calculations of the matrix elements are carried out by the Fock-Dirac multiconfiguration relativistic method using an intermediate type of coupling with orthogonal functions of the initial and final states. A single-electron wave function of the continuous spectrum for an Auger electron is obtained using the Fock-Dirac single-configuration method. The results of the calculations performed with orthogonal and nonorthogonal wave functions of the initial and final states are compared. The ionization cross sections are calculated for cases in which a knock-on electron of the continuous spectrum is described by both the orthogonal and nonorthogonal wave functions with respect to the wave functions of the core electrons.     

末态电子的关联在氢原子(e,2e)反应中的影响(英文)

在共面非对称几何条件下,利用双势公式解析计算了电子碰撞电离氢原子的三重微分截面.对快电子采用平面波近似,跃迁矩阵元可以表示成两个因子乘积的形式,即结构散射因子和出射道两电子的关联因子.在计算过程中对关联因子采取了最简单的近似,当入射能量为150 eV和54.4 eV时,计算结果与实验结果的符合说明对于这些入射能量该关联近似是有效的;而对于入射能量为27.2 eV时,计算结果与实验结果的较大差异说明这种关联近似是无效的.     

Scattering of atomic particles at relativistic energies

This article is concerned with excitation, ionization and electron capture collisions between charged particles and atomic systems involving a single active electron, at impact energies which are so great that Lorentz transformations between the frames of reference of the incident and target particles must be carried out as well as relativistic dynamics employed. For excitations and ionization it is sufficiently accurate to use the relativistic generalization of the first Born approximation, but for electron capture it is necessary to carry through the analysis using a relativistic generalization of the second Born approximation. Also relativistic wave functions are employed to describe the active atomic electron.     

强激光场中氢负离子双光子电离能量谱的研究

利用强场近似（Strong field approximation,SFA）方法研究氢负离子（H ）在强激光场中双光子电离的能量谱,所得到的电离谱随角度的变化规律与实验结果符合得很好.进一步的研究表明, H 离子在强激光场中双光子电离的能量谱与有质动力能有关.激光场强度越大,光电子的有质动力能也越大,能量谱向左移动越明显.我们的结果表明,使用强场近似是一种研究负离子在强激光场中电离过程的有效方法.