一氧化氮与para-H2碰撞的精细和超精细激发
Fine and hyperfine excitation of nitric oxide by collision with para-H2
摘要：
一氧化氮是一种开壳层分子，在星际介质中大量存在。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。我们在这里提出的第一速率系数的罚款和超精细（去）激发NO的碰撞与最普遍存在的碰撞伙伴在星际介质中，$para$-H $_2$氢分子，使用最近开发的准确的相互作用势。我们报告的量子散射计算的过渡涉及的前74个精细水平和相应的442个超精细水平属于$F_1$和$F_2$自旋轨道流形。为此，我们已经计算的横截面的量子力学紧耦合方法的装置高达1000厘米$^{-1}$的总能量和速率系数从5至100 K。倾向性规则进行了讨论，新的NO-H $_2$率进行了比较，在文献中提供的基础上缩放NO-He率。两组速率系数之间存在较大差异，这种比较表明，新的碰撞率必须用于解释NO发射线。通过对150.176和250.4368 GHz两条NO谱线的激发温度和亮度温度进行辐射转移计算，我们还研究了这些新速率对冷云中NO激发的影响。这表明，局部热力学平衡是不满足这种物种的典型条件。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。
英文摘要：
Nitric oxide is an open-shell molecule abundantly detected in the interstellar medium. A precise modeling 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, $para$-H$_2$ 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 $F_1$ and $F_2$ 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-H$_2$ 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.
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