Electron impact excitation of helium-like oxygen up to n = 4 levels including radiation damping
Electron impact excitation of helium-like oxygen up to n = 4 levels including radiation damping
复制标题
类氦氧的电子碰撞激发高达 n = 4 级，包括辐射阻尼
DOI：
10.1088/0953-4075/35/16/301
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
A. Pradhan
中科院分区：
文献类型：
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作者：
F. Delahaye;A. Pradhan
类氦离子的初级X射线诊断线主要由基态到n=2能级的电子碰撞激发，但在高温下n≥2能级也被激发。为了更完整地描述原子过程，首次计算了原子碰撞强度，包括：(I)相对论精细结构，(Ii)n=4能级，(Iii)自电离共振的辐射衰减。计算采用Breit-Pauli R-矩阵方法和31级本征函数展开。详细描述了直到n=4阈值的碰撞强度中的共振结构。对于高电荷态类氦离子，自电离共振的辐射衰减在某些能量范围内是显着的。我们对这一效应进行了详细的研究，发现当级数极限n→∞从下到下时，共振受到明显的辐射抑制，但对有效截面和速率系数的总体影响很小。给出了X射线等离子体诊断中重要的主线w，x，y和z的碰撞强度，它们对应于到基态1s2(1s0)←1s2p(1P1o)，1s2p(3p2o)，1s2p(3p1o)，1s2s(3s1)的四个跃迁。在几个转变上与以前的工作发现了显著的差异。研究发现，从n=4到复数n=4能级的共振对某些跃迁的贡献是显著的，并且可以将速率提高到原来的四倍。这项工作是作为Iron Project-RMAX网络的一部分进行的。
The primary x-ray diagnostic lines in He-like ions are mainly excited by electron impact from the ground level to the n = 2 levels, but at high temperatures n≥2 levels are also excited. In order to describe the atomic processes more completely, collision strengths are computed for O VII including for the first time all of the following: (i) relativistic fine structure, (ii) levels up to n = 4, and (iii) radiation damping of autoionizing resonances. The calculations are carried out using the Breit–Pauli R-matrix method with a 31-level eigenfunction expansion. Resonance structures in collision strengths are delineated in detail up to the n = 4 thresholds. For highly charged He-like ions radiation damping of autoionizing resonances is known to be significant in certain energy ranges. We investigate this effect in detail and find that while resonances are discernibly damped radiatively as the series limit n → ∞ is approached from below, the overall effect on effective cross sections and rate coefficients is found to be very small. Collision strengths for the principal lines important in x-ray plasma diagnostics, w, x, y and z, corresponding to the four transitions to the ground level 1s2(1S 0) ← 1s2p(1P 1o), 1s2p(3P 2o), 1s2p(3P 1o), 1s2s(3S 1), are explicitly shown. Significant differences are found with previous works for several transitions. The contribution from the resonances converging to the levels from the complex n = 4 is found to be significant for some transitions and can increase the rate by a factor of four. This work is carried out as part of the Iron Project-RmaX Network.