Electron impact excitation and ionization with atoms and ions within a dense plasma are fundamental microscopic processes that determine the ionization balance, physical properties (such as electron conductive opacity and thermal conductivity) and plasma formation and dynamics. While collision cross-sections and rates are well studied in dilute systems, similar investigations are scarce for dense plasmas under stellar interior conditions using an appropriate plasma-screening potential. Here we investigate the plasma-screening effect on the electron impact excitation and ionization cross-sections, effective collision strengths, and rate coefficients within plasmas under stellar interior conditions in a mass density range of 1–15.748 g cm−3 and a temperature range of 200–1000 eV. These investigations were carried out using our recently developed plasma-screening model, taking Fe16+ as an example. The results show that the cross-sections of the electron impact excitation are generally decreased, whereas they are always significantly increased for the collision ionization due to the plasma screening. In a plasma at a temperature of 200 eV and density of 15.748 g cm−3, the plasma screening causes a decrease in the excitation cross-section of 36 per cent for the dipole-allowed transition $2\mathrm{ s}^22\mathrm{ p}^6~^1\mathrm{ S}_0 \rightarrow 2\mathrm{ s}^22\mathrm{ p}^53\mathrm{ d}~^1\mathrm{ P}^o_1$ and of 50 per cent for the dipole-forbidden transition $2\mathrm{ s}^22\mathrm{ p}^6~^1\mathrm{ S}_0 \rightarrow 2\mathrm{ s}^22\mathrm{ p}^53\mathrm{ d}~^3\mathrm{ D}^o_1$. However, the collision ionization cross-section of a 2p electron from the ground level of Fe16+ is increased by 500 per cent and 100 per cent under an incident electron energy of 1500 and 10 000 eV, respectively. This results in the rate coefficient increasing by a factor of 18.5 at a temperature of 200 eV and density of 15.748 g cm−3.

中文翻译：

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等离子筛选对高密度环境下 Fe16+ 电子碰撞激发和电离的影响

电子撞击激发和与密集等离子体中的原子和离子的电离是决定电离平衡、物理性质（例如电子传导不透明度和热导率）以及等离子体形成和动力学的基本微观过程。虽然在稀释系统中对碰撞截面和碰撞速率进行了很好的研究，但对于在恒星内部条件下使用适当的等离子体筛选势的致密等离子体，类似的研究很少。在这里，我们研究了在质量密度范围为 1-15.748 g cm-3 和温度范围为200–1000 电子伏特。这些研究是使用我们最近开发的等离子筛选模型进行的，以 Fe16+ 为例。结果表明，由于等离子体屏蔽，电子碰撞激发的横截面普遍减小，而碰撞电离的横截面总是显着增加。在温度为 200 eV、密度为 15.748 g cm-3 的等离子体中，等离子体屏蔽导致偶极子允许跃迁 $2\mathrm{ s}^22\mathrm 的激发截面减少 36% { p}^6~^1\mathrm{ S}_0 \rightarrow 2\mathrm{ s}^22\mathrm{ p}^53\mathrm{ d}~^1\mathrm{ P}^o_1$ 和 50偶极禁止跃迁的百分比 $2\mathrm{ s}^22\mathrm{ p}^6~^1\mathrm{ S}_0 \rightarrow 2\mathrm{ s}^22\mathrm{ p}^53\ mathrm{ d}~^3\mathrm{ D}^o_1$。然而，在 1500 和 10 000 eV 的入射电子能量下，来自 Fe16+ 地平面的 2p 电子的碰撞电离截面分别增加了 500% 和 100%。这导致在 200 eV 的温度和 15.748 g cm-3 的密度下，速率系数增加了 18.5 倍。