双电子复合过程的相对论理论研究 通道的变化特性

双电子复合是一种共振辐射复合过程,在这一过程中,一个具有特定能量的自由电子与电离度为q的离子A~(+q)碰撞,形成有两个电子激发的自电离态n_(?)l_(?)nl,该自电离态进一步发射光子,复合成A~(+(q-1))离子,一系列n(?)l_(?)nl自电离态(n_(?)l_(?)l固定,n从有限到无限变化)形成一个通道,本文在相对论单组态理论基础上,具体探讨了类氦铁离子(3s_(1/2)~nP_(1/2))J=(?)通道中,双电子复合速率随n的变化规律,根据本文得到的规律,可以很方便地计算任意离子的任意一 关键词：     

Detection of the 1pe series of doubly excited helium states below N=2 via the stark effect

The Stark effect on the doubly excited states of helium below the N=2 threshold has been studied by vacuum ultraviolet fluorescence yield spectroscopy. Two new series of states are observed at moderate fields (<10 kV/cm), and assigned to the previously unobserved even 1pe series, and a group of 1De series. The 1Se states are observed indirectly via their mixing with nearby 1 po states. The observations at moderate field contradict theoretical predictions that field strengths about an order of magnitude greater are necessary to observe the Stark effect on He doubly excited states at low quantum numbers.     

类铍Ar^14＋和类镁Ar^6＋离子双激发态能级的计算

用相态相互作用方法计算了类铍Ａｒ＾１４＋离子双激发态１ｓ＾２３ｌ３ｌ＇和类镁Ａｒ＾６＋离子双激发态１ｓ＾２２ｓ＾２２ｐ＾６４ｌ４ｌ＇的能级。两个外层电子与内层原子实１ｓ＾２或１ｓ＾２２ｓ＾２２ｐ＾６电子的作用用模型势表不。Ａｒ＾１４＋的双激发态可用量子数Ｋ，Ｔ和Ａ标记，而Ａｒ＾６＋的某些组态却不能用上述量子数表示。     

Investigation of the electronic structure of Be2+He and Be+He,and static dipole polarisabilities of the helium atom

The potential energy and spectroscopic constants of the ground and many excited states of the Be⁺He van der Waals system have been investigated using a one-electron pseudo-potential approach, which is used to replace the effect of the Be²⁺ core and the electron-He interactions by effective potentials. Furthermore, the core–core interactions are incorporated. This permits the reduction of the number of active electrons of the Be⁺He van der Waals system to only one electron. Therefore, the potential energy of the ground state as well as the excited states is performed at the SCF level and considering the spin–orbit interaction. The core–core interaction for Be²⁺He ground state is included using accurate CCSD (T) calculations. Then, the spectroscopic properties of the Be⁺He electronic states are extracted and compared with the previous theoretical and experimental studies. This comparison has shown a very good agreement for the ground and the first excited states. Moreover, the transition dipole moment has been determined for a large and dense grid of internuclear distances including the spin orbit effect. In addition, a vibrational spacing analysis for the Be²⁺He and Be⁺He ground states is performed to extract the He atomic polarisability.     

Young-type experiment using a single-electron source and an independent atomic-size two-center interferometer

Evidence is given for Young-type interferences caused by a single electron acting on a given double-center scatterer analogous to an atomic-size double-slit system. The electron is provided by autoionization of a doubly excited He atom following the capture of the electrons of H2 by a He2+ incoming ion. The autoionizing projectile is a single-electron source, independent of the interferometer provided by the two H+ centers of the fully ionized H2 molecule. This experiment resembles the famous thought experiment imagined by Feynman in 1963, in which the quantum nature of the electron is illustrated from a Young-like double-slit experiment. Well-defined oscillations are visible in the angular distribution of the scattered electrons, showing that each electron interferes with itself.     

超短脉冲激光场中间二氯苯的激发态动力学

利用飞秒时间分辨的飞行时间质谱技术研究了间二氯苯的激发态动力学.间二氯苯分子吸收一个200 nm或者267 nm的光子被抽运到激发态,随后再吸收多个800 nm的光子被电离.实验获得了电离产生的离子质谱信号及其随抽运探测激光延迟时间的变化曲线.在200 nm时,分子被抽运到激发态(π,π*),可观察到三个相互竞争的解离通道的寿命:内转换到排斥态(n,σ*)或者(π,σ*)并发生快速解离,其寿命约(0.15±0.01)ps;内转换到基态的高振动态,能量在基态"热"振动态间弛豫的寿命约为(4.94±0.08)ps;系间窜越到相邻的三重态从而发生预解离过程,其寿命约为(110.09±4.33)ps.在267 nm时,分子被抽运到第一激发态的低振动态,可观察到一个长寿命(约(1.06±0.05)ns)的系间窜越过程.除此之外,在碎片离子信号中还观察到了激发态与基态的高振动态之间的内转换过程.     

激发态之间的电离与复合过程对类氖锗19.6nm X射线激光增益系数的影响

考察了激发态之间的电离与复合过程对等离子体状态的影响,并对其原因进行了细致的分析,分别考察了对1.0ns,100ps和5ps激光驱动的类氖锗19.6nm Ｘ射线激光增益系数的影响.研究表明,对于5ps激光驱动的瞬态机理X射线激光来讲,因增益区处在高密度区,所以,激发态之间的电离与复合过程对X射线激光将不可以忽略.对于1.0ns和100ps激光驱动的亚稳态机理X射线激光来讲,在电子密度小于等于5×10²⁰cm^－3的区域,忽略激发态之间的电离与复合使增益的时间半高全 关键词： X射线激光 矩阵分块法 类氖锗 双电子激发态     

Nonperturbative treatment of ionization with excitation of helium by electron impact

We present cross sections for electron-impact ionization and simultaneous ionization plus excitation of helium by electron impact. The results are obtained from a fully nonperturbative close-coupling formalism using our B-spline R-matrix approach. A large number of pseudostates in the expansion of the wave function represent the coupling to the ionization continuum. We obtain excellent agreement with the directly measured experimental cross section ratios (Bellm et al., Phys. Rev. A 75, 042704 (2007)) for ionization leaving the residual He? ion in either the 1s ground state or the n = 2 (2s + 2p) excited states.     

Investigation of ion-atom collision dynamics through imaging techniques

The principle and technique details of recoil ion momentum imaging are discussed and summarized. The recoil ion momentum spectroscopy built at the Institute of Modern Physics (Lanzhou) is presented. The first results obtained at the setup are analyzed. For 30 keV He²⁺ on He collision, it is found that the capture of single electron occurs dominantly into the first excited states, and the related scattering angle results show that the ground state capture occurs at large impact parameters, while the capture into excited states occurs at small impact parameters. The results manifest the collision dynamics for the sub-femto-second process can be studied through the techniques uniquely. Finally, the future possibilities of applications of the recoil ion momentum spectroscopy in other fields are outlined. Supported by the National Natural Science Foundation of China (Grant No. 10434100)     

Breakup of H2 in singly ionizing collisions with fast protons: channel-selective low-energy electron spectra

Dissociative as well as nondissociative single ionization of H2 by 6 MeV proton impact has been studied in a kinematically complete experiment by measuring the momentum vectors of the electron and the H+ fragment or the H+2 target ion, respectively. For the two ionization pathways, the electron spectra reveal the role of autoionization of the doubly and singly excited states of H2. The latter explicitly involve the coupling between the electronic and the nuclear motion of the molecule. This is a clear manifestation of a breakdown of the Born-Oppenheimer approximation.     

Observation of triplet doubly excited states in single photon excitation from ground state helium

We have observed, for the first time, LS-forbidden triplet doubly excited states, in single photon excitation of ground state helium, below the second ionization threshold. These states are identified as (3)D(o) and (3)P(o) and their excitation is due to spin-orbit interaction that mixes them with the optically allowed (1)P(o) states. This observation is possible due to the very high efficiency in detecting metastable atoms created after the fluorescence decay of the doubly excited states, and the new capabilities of third generation synchrotron vacuum ultraviolet sources with high resolution beam lines.     

Electric field controlled, pulsed autoionization in two electron wave packets

In this paper, control of the evolution of a two electron wave packet through the application of a static electric field is demonstrated. Specifically, application of a small electric field is used to produce pulsed autoionization events, the timing of which can be controlled on a picosecond time scale. The technique is demonstrated by exciting calcium atoms using a short-pulsed laser to the 4p(3/2)19d doubly excited state, which is energy degenerate with the 4p(1/2)nk stark states. Evolution of the resultant wave packet is monitored through the application of a second short laser pulse, which stimulates the atoms to emit a photon producing singly excited Rydberg states which are detected using field ionization.     

Resonant coherent excitation of Ar17+ ions taking into account a fine structure of energy levels

The effect of a fine structure of the orbital electron energy levels of an Ar¹⁷⁺ ion on the resonant coherent excitation under planar channeling has been investigated by computer simulation technique. The obtained resonance curves are characterized by two closely situated peaks due to the transitions of an electron from the ground to excited states corresponding to the different components of a fine structure of the first excited state which differ in the value of the total electron momentum (1/2 or 3/2).     

Neutralization mechanisms in He-Al surface collisions

From a quantum mechanical calculation where the populations of He ground and first excited states are properly taken into account, we can identify for the first time the neutralization to the He first excited state as an operative mechanism in He⁺-Al surface collisions. This identification allows us to understand the presence of high energy electrons in the ion induced electron emission spectra, through the inclusion of Auger deexcitation as an electron emission source, as well as to suggest a possible cause for the disagreement still found between theory and experiments in low energy ion scattering (LEIS) for this system.     

Formation of doubly excited He atoms during scattering of He ions from a clean and oxygen covered Ni(1 1 0) surface

The formation of doubly excited states of He atoms during collisions of He²⁺ ions with energies between 60 eV and 1 keV with a Ni(1 1 0) surface is studied via Auger electron spectroscopy. We observe that the electron spectra from autoionization of doubly excited states of 2s², 2s2p, 2p² configurations show a pronounced dependence on the coverage of the target surface with oxygen. For a controlled O₂ adsorption on the Ni(1 1 0) surface we can explain the resulting changes in the electron spectra by the modification of the work function of the target surface. Thermal desorption and dissolution into the bulk of surface contaminations at elevated temperatures provides an alternative interpretation of recent work where the local electron spin polarization of a Ni(1 1 0) surface was deduced from changes in the electron spectra as function of target temperature.     

Effects of adsorbates on the formation of doubly excited He atoms during impact of He2+ ions on Fe(110) and Ni(110) surfaces

The formation of doubly excited states of He atoms during collisions of He²⁺ ions with projectile energies between 74 eV and 124 eV with an Fe(110) and a Ni(110) surface is studied via Auger electron spectroscopy. We observe that the electron spectra from autoionization of doubly excited states of 2s², 2s2p, 2p² configurations show a pronounced dependence on the coverage with oxygen for both surfaces. For a controlled O₂ adsorption on the Fe(110) and Ni(110) surfaces we can explain the resulting changes in the electron spectra by the modification of the measured work functions of the target surfaces. In terms of thermal desorption and dissolution into the bulk of surface contaminations at elevated temperatures, we present an alternative interpretation of similar previous studies by another group, where the local electron spin polarization of Fe(110) and Ni(110) surfaces was deduced from changes in the electron spectra as function of target temperature.     

Editorial

A high resolution electron spectroscopy technique is used to study the autoionization of noble gases excited by fast neutral noble gas atoms with 80–600 eV kinetic energy. The energy and notation of the excited states is determined by considering the proper quantum defects in the Rydberg series. The doubly excited states prevail over the singly excited ones. Like and unlike colliding pairs are studied and various excitation processes are suggested for the HeKr, ArKr and ArXe systems.     

Energies and electron correlation effects in two-electron doubly excited (nl)2 states

Energies of singlet doubly excited states 2p^{2 1}D, 3d^{2 1}G, 4f^{2 1}I of He isoelectronic series are calculated in the framework of the variational method by using Hylleraas-type wave functions and a real Hamiltonian. The results obtained show quantitatively the importance of electron correlation effects in the doubly excited states and they are in good agreement with some experimental data and other theoretical results. Received 30 March 2000 and Received in final form 4 July 2000     

S-matrix study on alignment dependence of single ionization of molecular ions with different active orbitals

The orientation-dependent single ionization rate of the diatomic molecular ion H_2^+ with different active orbitals in an intense field is studied by using S-matrix theory. Our results show that the orientation-dependent single ionization probability of H_2^+ is greatly dependent on the symmetry and the electron density distribution of its initial states, and it can be used to identify the excited state of the molecular ion in the dissociation process.     

高电荷态离子N6+与He原子碰撞激发过程的实验研究

利用电子迴旋共振(ECR)多电荷离子源产生的高电荷态离子束和LHT-30VUV真空紫外单色仪,对N⁶⁺与He碰撞激发过程进行研究,观察到三种碰撞激发过程:(1)单电子俘获;(2)双电子俘获;(3)入射离子直接激发过程。 关键词：