Dielectronic Recombination of Fe XIX Forming Fe XVIII: Laboratory Measurements and Theoretical Calculations: Data

We have measured resonance strengths and energies for dielectronic recombination (DR) of Fe XIX forming Fe XVIII via N = 2 → N' = 2 and N = 2 → N' = 3 core excitations. All measurements were carried out using the heavy-ion Test Storage Ring at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We have also calculated these resonance strengths and energies using two independent, state-of-the-art techniques: the perturbative multiconfiguration Breit-Pauli (MCBP) and multiconfiguration Dirac-Fock (MCDF) methods. Overall, reasonable agreement is found between our experimental results and theoretical calculations. The most notable discrepancies are for the 3l3l' resonances. The calculated MCBP and MCDF resonance strengths for the n = 3 complex lie, respectively, ≈47% and ≈31% above the measured values. These discrepancies are larger than the estimated ≲ 20% total experimental uncertainty in our measurements. We have used our measured 2 → 2 and 2 → 3 results to produce a Maxwellian-averaged rate coefficient for DR of Fe XIX. Our experimentally derived rate coefficient is estimated to be good to better than ≈20% for kBTe ≥ 1 eV. Fe XIX is predicted to form in photoionized and collisionally ionized cosmic plasmas at kBTe Gt 1 eV. Hence, our rate coefficient is suitable for use in ionization balance calculations of these plasmas. Previously published theoretical DR rate coefficients are in poor agreement with our experimental results. None of these published calculations reliably reproduce the magnitude or temperature dependence of the experimentally derived rate coefficient. Our MCBP and MCDF results agree with our experimental rate coefficient to within ≈20%.

本研究针对铁十九离子（Fe XIX）通过N=2→N'=2与N=2→N'=3芯激发过程的双电子复合（dielectronic recombination, DR）生成铁十八离子（Fe XVIII）的共振强度与共振能量开展了实验测量。所有实验均依托德国海德堡马克斯·普朗克核物理研究所（Max Planck Institute for Nuclear Physics）的重离子实验储存环（Heavy-ion Test Storage Ring）完成。本研究同时采用两种独立的前沿技术对上述共振强度与共振能量进行了理论计算：微扰多组态Breit-Pauli（MCBP）方法与多组态Dirac-Fock（MCDF）方法。整体而言，实验结果与理论计算结果吻合度较好，但针对3l3l'共振态存在较为显著的偏差：针对n=3组态的MCBP与MCDF计算所得共振强度分别比实验测量值高出约47%与31%，该偏差大于本次实验估算的总实验不确定度（≤20%）。本研究利用测得的2→2与2→3过程实验数据，推导得到了铁十九离子双电子复合的麦克斯韦平均速率系数。经估算，当k_B T_e ≥ 1 eV时，本实验得到的速率系数的不确定度优于约20%。铁十九离子会在k_B T_e ≳ 1 eV的光致电离与碰撞电离宇宙等离子体中形成，因此本研究得到的速率系数可用于此类等离子体的电离平衡计算。已发表的相关理论DR速率系数与本实验结果吻合度较差，均未能可靠复现实验所得速率系数的幅值与温度依赖关系。本研究的MCBP与MCDF理论计算结果与实验速率系数的偏差均在约20%以内。