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Fine and hyperfine excitation of nitric oxide by collision with para-H2 at low temperature
Monthly Notices of the Royal Astronomical Society ( IF 4.7 ) Pub Date : 2021-09-15 , DOI: 10.1093/mnras/stab2630
M Ben Khalifa 1 , J Loreau 1
Affiliation  

Nitric oxide is an open-shell molecule abundantly detected in the interstellar medium. A precise modelling of its radiative and collisional processes opens the path to a precise estimate of its abundance. We present here the first rate coefficients for fine and hyperfine (de-)excitation of NO by collisions with the most ubiquitous collision partner in the interstellar medium, para-H2 hydrogen molecules, using a recently developed accurate interaction potential. We report quantum scattering calculations for transitions involving the first 74 fine levels and the corresponding 442 hyperfine levels belonging to both F1 and F2 spin–orbit manifolds. To do so, we have calculated cross-sections by means of the quantum mechanical close-coupling approach up to 1000 cm−1 of total energy and rate coefficients from 5 to 100 K. Propensity rules are discussed and the new NO–H2 rates are compared to those available in the literature, based on scaled NO–He rates. Large differences are observed between the two sets of rate coefficients, and this comparison shows that the new collision rates must be used in interpreting NO emission lines. We also examined the effect of these new rates on the NO excitation in cold clouds by performing radiative transfer calculations of the excitation and brightness temperatures for the two NO lines at 150.176 and 250.4368 GHz. This shows that the local thermodynamic equilibrium is not fulfilled for this species for typical conditions. We expect the use of the rates presented in this study to improve the constraints on the abundance of NO.

中文翻译:

低温下与对氢碰撞对一氧化氮的精细和超精细激发

一氧化氮是一种在星际介质中大量检测到的开壳分子。对其辐射和碰撞过程的精确建模为精确估计其丰度开辟了道路。我们在这里使用最近开发的精确相互作用势,通过与星际介质中最普遍的碰撞伙伴对 H2 氢分子的碰撞,展示 NO 的精细和超精细(去)激发的第一速率系数。我们报告了涉及前 74 个精细能级和属于 F1 和 F2 自旋轨道流形的相应 442 个超精细能级的跃迁的量子散射计算。为此,我们通过量子力学紧密耦合方法计算了高达 1000 cm-1 的总能量和从 5 到 100 K 的速率系数的横截面。讨论了倾向规则,并将新的 NO-H2 比率与文献中可用的比率进行了比较,基于缩放的 NO-He 比率。两组速率系数之间存在很大差异,这种比较表明,必须使用新的碰撞速率来解释 NO 排放线。我们还通过对 150.176 和 250.4368 GHz 的两条 NO 线的激发和亮温进行辐射传递计算,检查了这些新速率对冷云中 NO 激发的影响。这表明该物种在典型条件下不满足局部热力学平衡。我们期望使用本研究中提出的速率来改善对 NO 丰度的限制。两组速率系数之间存在很大差异,这种比较表明,必须使用新的碰撞速率来解释 NO 排放线。我们还通过对 150.176 和 250.4368 GHz 的两条 NO 线的激发和亮温进行辐射传递计算,检查了这些新速率对冷云中 NO 激发的影响。这表明该物种在典型条件下不满足局部热力学平衡。我们期望使用本研究中提出的速率来改善对 NO 丰度的限制。两组速率系数之间存在很大差异,这种比较表明,必须使用新的碰撞速率来解释 NO 排放线。我们还通过对 150.176 和 250.4368 GHz 的两条 NO 线的激发和亮温进行辐射传递计算,检查了这些新速率对冷云中 NO 激发的影响。这表明该物种在典型条件下不满足局部热力学平衡。我们期望使用本研究中提出的速率来改善对 NO 丰度的限制。我们还通过对 150.176 和 250.4368 GHz 的两条 NO 线的激发和亮温进行辐射传递计算,检查了这些新速率对冷云中 NO 激发的影响。这表明该物种在典型条件下不满足局部热力学平衡。我们期望使用本研究中提出的速率来改善对 NO 丰度的限制。我们还通过对 150.176 和 250.4368 GHz 的两条 NO 线的激发和亮温进行辐射传递计算,检查了这些新速率对冷云中 NO 激发的影响。这表明该物种在典型条件下不满足局部热力学平衡。我们期望使用本研究中提出的速率来改善对 NO 丰度的限制。
更新日期:2021-09-15
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