Auroral N2 emissions and the effect of collisional processes on N2 triplet state vibrational populations
Auroral N2 emissions and the effect of collisional processes on N2 triplet state vibrational populations
复制标题
极光 N2 排放和碰撞过程对 N2 三重态振动群体的影响
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
W. Benesch
中科院分区：
文献类型：
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作者：
J. Morrill;W. Benesch
以前的模型结果表明，极光中的N_2三重态能级布居受到原子和分子氧的级联和猝灭的强烈影响。随着极光穿透到较低的高度(不到100公里)，原子氧猝灭的作用变得不那么重要，而涉及氮气碰撞的过程开始发挥更重要的作用。我们正在开发一个模型，它将产生N_2的单重态和三重价态的稳态振动能级布居。该模型目前提供了七个低位N 2三重态(A 3Σu+，B3IIg，W3Δu，B‘3Σu−，C3IIu，D3Σu+，和E3Σg+)的结果。这些状态负责从紫外线(Vegard-Kaplan(VK)，第二正(2PG))到可见光到红外(第一正(1PG)，红外余辉(IRA)，Wu-Benesch(WB))的极光发射。我们在目前的模型中包括了两个以前没有处理的额外的碰撞过程。这是B态与A、W和B‘态之间的系统间碰撞激发转移(ICT)和A态振动流形内的振动重分布，两者都是由于与基态N_2的碰撞而引起的。本工作将我们目前的模型结果与以前的模型以及地面、空中和火箭观测的结果进行了比较。由我们的模型预测的N_2(A)(VK)和N_2(B)(1PG)振动能级布居与大量极光观测结果的比较表明，目前的模型在计算和观测之间的吻合程度有了显著的提高。此外，目前的模型预测了1PGΔν=3序列的波段强度分布将在较低高度(小于90公里)从红外向可见红色移动，以及整个1PG系统的整体增强。因此，这为b型极光的一个主要特征提供了可能的解释，即极光红色下边界。
Previous model results have shown that the N2 triplet vibrational level populations in the aurora are strongly affected by cascade and quenching by atomic and molecular oxygen. As the aurora penetrates to lower altitudes (less than 100 km) the role of quenching by atomic oxygen becomes less important and processes involving N2 collisions begin to play a more prominent part. We are developing a model which will yield steady state vibrational level populations for both the singlet and triplet valence states of N2. The model currently provides results for the seven low-lying N2 triplet states (A 3Σu+, B 3IIg, W3Δu, B′ 3Σu−, C3IIu, D3Σu+, and E3Σg+). These states are responsible for auroral emissions from the UV (Vegard-Kaplan (VK), second positive (2PG)) through the visible to the infrared (first positive (1PG), infrared afterglow (IRA), Wu-Benesch (WB)). We have included two additional collisional processes in the current model which were not treated previously. These are the intersystem collisional transfer of excitation (ICT) between the B state and the A, W, and B′ states and vibrational redistribution within the A state vibrational manifold, both due to collisions with ground state N2. The present work compares our current model results with those of a previous model, as well as ground, airborne, and rocket observations. The comparison between N2(A) (VK) and N2(B) (1PG) vibrational level populations predicted by our model and a number of auroral observations indicate that the current model achieves a significant improvement in the fit between calculation and observation. In addition, the current model predicts a shift in the band intensity distribution of the 1PG Δν = 3 sequence from the infrared into the visible red at the lower altitudes (less than 90 km) as well as an overall enhancement in the entire 1PG system. Consequently, this provides a possible explanation of a dominate feature of type b aurora, the auroral red lower border.