Evidence of simultaneous double-electron promotion in F+ collisions with surfaces

A high-flux beam of mass-filtered F+ at low energy (100-1300 eV) was scattered off Al and Si surfaces to study core-level excitations of F0 and F+. Elastic scattering behavior for F+ was observed at energies <300 (500) eV off Al (Si) for a 90 degrees lab angle. However, above this energy threshold, orbital mixing in the hard collision step results in electronic excitation of F via molecular orbital promotion along the 4f sigma (F-2p), significantly reducing the observed ion exit energy. In addition, despite the electronegativity of F, scattering at energies >450 (700) eV off Al (Si) produces F2+-behavior which is remarkably similar to Ne+ off the same surfaces. Inelasticities measured for single collision events agree well with the energy deficits required to form (doubly excited) F** and F+** states from F0 and F+, respectively; these excited species most likely decay to inelastic F+ and F2+ via autoionization.     

用紧耦合方法研究C4+和O6+与He原子碰撞

用双中心原子轨道紧耦合方法计算了C4+-He以及O6+-He碰撞的单俘获总截面,入射离子的能量范围为10～100keV/amu,所得计算结果在实验误差范围内与实验值很好符合.对满壳层入射离子,研究了单俘获截面随入射离子电荷态的变化,并讨论了原子轨道展开波函数数目对计算结果的影响.p     

Angular dependence of double electron capture in collisions of C4+ with He

In charge-transfer collisions of C⁴⁺(1s^{2 1}S) with He (1s^{2 1}S), the process of double electron capture into the ground state C²⁺ is well-known to dominate other channels by an order of magnitude for projectile energies below 10 keV. This work presents a calculation of differential cross-sections resolved in the angle and energy gain variables, based on an ab initio treatment of electronic states, and compares with the measurements published in the literature (projectile energy E=270, 400, and 470 eV). We also briefly discuss the semi-empirical two-state models developed by experimentalists for this process.     

Double electron capture cross-sections by protons in collisions with He

Double electron capture (DEC) by protons from He was studied in collisions at energies in the keV regime, theoretically and experimentally. Theoretical cross-sections were calculated using the electron nuclear dynamic approach and a binomial distribution method in the energy range 1–100 keV. Experimental cross-sections were measured by means of the grow-rate method in the energy range of 4–10 keV. The cross-sections measured are consistent with those of the previous data at the high energies of the measured interval and show a different trend for the low energy. This behavior is consistent with those of other DEC cross-sections measured by protons from He-like targets. With the two collision models, it is proven that the reference data for this system are consistent only with the assumption of uncorrelated electrons and with independent target-projectile nuclei dynamics.     

低能He2+-He反应中单电子俘获微分散射过程的实验研究

利用冷靶反冲离子动量谱仪装置系统研究了20-40 keV He2+-He碰撞体系的态选择单电子俘获过程,实验获得了单电子俘获过程的态选择截面以及角微分截面.在所研究的能区范围,电子俘获到L壳层的截面最大,为主要的反应道,这与分子库仑过垒模型的反应窗理论的预测一致.实验测量的态选择截面与原子轨道紧耦合的计算结果很好地符合,与光谱方法的测量结果存在一定的差别,主要原因是光谱方法不能测量完整的反应通道信息.实验结果表明,总角微分截面在小角度范围主要来源于电子俘获到基态的贡献,在大角度范围主要来自电子俘获到激发态的贡献;电子俘获到基态的和激发态的角微分截面均出现振荡结构,这种振荡来源于电子俘获反应中分子轨道之间的相干效应.实验测量的角微分截面与其他实验和紧耦合方法的计算结果进行了比较和分析.     

O5+离子与H原子碰撞时电子俘获概率的计算

利用原子轨道作基函数展开系统波函数，附加电子转移因子修正O５＋离子和H原子相互作用时的边界条件，计算了初始通道的势能.在得出的理论值与实验值符合很好的情况下，验证了计算参数的可靠性.在碰撞参数b=80a.u.,碰撞速度v=2200a.u.的条件下，利用心核近似方法完成了O５＋离子和H原子碰撞过程中8个Σ状态的随时间变化电子俘获概率的理论计算. 关键词： O５＋离子 H原子 碰撞 电子俘获     

Charge distribution of He states, excited by electron capture in He+ (26 keV)-He collisions

Using anticrossing spectroscopy we investigated one-electron capture in He⁺ (26 keV) – He collisions. The intensity of the triplet line λ (1s4l ³D → 1s2p ³P) ≈ 447.2 nm emitted by the fast atoms was measured as a function of an external electric field in the collision volume varied from ?30 kV/cm to +30 kV/cm. The radiative decay of excited He atoms in an almost field-free region outside the collision volume was observed. The highly asymmetric intensity function could be reproduced theoretically using the density-matrix formalism. It indicates that the excited He atoms are in a state with a highly forward-backward asymmetric charge distribution, immediately after the charge-exchange collision.     

Two-electron description of electron transfer in He++He+ collisions

Electron transfer in He⁺ + He⁺ collisions is studied within the two-electron form of the atomic-orbital expansion method. The population of both singlet and triplet helium states is considered. The calculated total and partial transfer cross sections agree well with available experimental data. Deviations from results of other calculations and the transfer mechanism in the triplet channel are discussed.