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本文利用“二态矢量模型”详细研究了高电荷态O7+、N6+离子入射Al表面时中间里德堡态的形成过程,给出了电子被俘获至不同量子数nA=2-7)的几率,以及电子俘获至里德堡态最可能的离子-表面距离。计算结果表明,较大的主量子数nA对应较小的里德堡态几率,因此O7+、N6+离子入射Al表面时辐射的X射线主要来源于较小的nA至基态的退激。为了验证计算结果,我们测量了O7+、N6+ 离子入射Al 表面的X射线发射谱,并运用FAC程序计算了不同高里德堡态退激到基态的跃迁能(np-1s)。实验测量到O、N 的K-X射线峰,其特征峰的中心值接近主量子数n=2至n=1的跃迁能,说明发射的X 射线主要来源于2p-1s的跃迁,与“二态矢量模型”理论计算的几率一致。The study of the interaction between highly charged ions and solid surfaces not only has great significance for basic scientific research such as atomic physics, astrophysics, and high energy density physics but also has promising application prospects in biomedicine, nanotechnology, surface analysis, and microelectronics. In this paper, the intermediate Rydberg states formed during highly charged O7+ and N6+ ions incident on Al surface are studied theoretically by using the two-state vector model. Both the probability of electron capture into different Rydberg states (nA = 2 − 7) and the most probable neutralization distances are given. The calculation shows that the larger principal quantum number nA is relevant to smaller probability. Therefore, the X-rays emitted by O7+ and N6+ ions incident on the Al surface come mainly from the de-excitation of the smaller nA to the ground state. In order to confirm the calculations, we measured the X-ray emission spectra of O7+ and N6+ ions in collisions with the Al surface in the energy range of 3-20 keV/q. The experiments were performed at an ECR ion source located in Institute of modern physics. We also calculated the transition energies (np-1s) from different high Rydberg states to the ground state by using the FAC code. The center of the measured K X-ray peak is close to the calculated transition energy from the principal quantum number n=2 to n=1, it is consistent with our results obtained by the two-state vector model as well. In addition, we found the experimental K X-ray yield for O7+ ions incidence at lower energy collisions is almost the same with N6+ ions, but larger at higher energy collisions. When the ion incident kinetic energy is low, the X-ray emission is mainly owing to the decay of “above the surface”hollow atoms. Because of the small difference in the critical distances for the capture of electrons by O7+ and N6+ to form hollow atoms, the X-ray yields produced in both cases are almost the same at low energy collisions. In contrast, as increasing the incident energy, the ions have a long-range in the target, so the contribution from the decay of “above the surface” and “below the surface”hollow atoms need to be considered at the same time.
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Keywords:
- highly charged ions /
- Rydberg states /
- the twostate vector model /
- X-rays
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