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低能高电荷态离子与H原子电荷交换X射线发射及天文应用

X-ray Emission Following Charge Exchange Between Slow Highly Charged Ions and Atomic H and Its Astronomical Application

  • 摘要: 低能高电荷态离子与H原子电荷交换X射线的实验和理论研究为天体环境中非平衡态等离子体的诊断和建模提供了重要原子数据。本工作利用半经典多通道Landau-Zener (MCLZ)方法计算了全裸和类氢的C、N、O离子与H原子电荷交换截面并与已报道实验结果进行了比较。我们发现,对于 \rm C^5++H 碰撞体系,理论计算的总截面和实验测量相差较大。同时,也对比了太阳风离子速度(或能量)区间MCLZ方法和全量子分子轨道紧耦合(QMOCC)方法计算的态选择截面。发现,对于俘获到 n=3 壳层,MCLZ方法计算的态选择截面随碰撞能量升高而增加;对于俘获到 n = 4 壳层,MCLZ方法计算的态选择截面随碰撞能量升高而减小;在低能端比QMOCC方法计算的截面小两个量级之多。最后,采用天文领域发展的Kronos程序包,通过Janev推荐的截面数据Atomic Data and Nuclear Data Tables, 1999, 55(2):201 计算了1 keV·u−1 \rm O^8+ + H 电荷交换X射线谱、线强比及硬度比,并与MCLZ计算结果比较。我们认为,MCLZ计算方法结合 l 分布模型具有较大的不确定性,会影响天体环境建模的准确性。亟需发展更加准确的全量子理论。

     

    Abstract: Experimental and theoretical research on X-ray emissions following charge exchange between slow highly charged ions and atomic Hydrogen supply vital atomic data for the study of diagnosing and modeling plasmas in non-equilibrium astrophysical environment. In the present paper, employing the semiclassical multi-channel Landau-Zener (MCLZ) method, we calculated the total cross-section of bare and hydrogenic C, N, and O ions charge exchange with hydrogen atoms, and compared it with previously reported experimental results. In \rm C^5+ + H collision, theoretically calculated cross-sections have large differences with experimental cross-sections. We also compared state-selective cross-sections calculated by classical MCLZ and quantum-mechanical molecular orbital close-coupling (QMOCC) methods in the solar wind ion velocity (or energy) range. For capture to n = 3 shell, MCLZ calculated state-selective cross-section increases with collision energy increasing; For capture to n = 4 shell, MCLZ calculated state-selective cross-section decreases with collision energy increasing; It is lower than two magnitudes as the QMOCC method calculated cross-section at the low energy end. Finally, using the Kronos program package developed in the astrophysical field, we calculated the X-ray emission spectrum, line ratio, and hardness ratio of charge exchange of 1 keV·u−1 \rmO^8++\rmH by means of the recommended cross-section by Janev Atomic Data and Nuclear Data Tables, 1999, 55(2): 201, and contrast with the MCLZ method calculated results. We consider that the MCLZ calculation combine with l distribution model has a large uncertainty, which could affect the accuracy of the astrophysical environment modeling. It is required to develop a more accurate full quantum theory.

     

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