ALMA-PILS调查：在星际介质中首次探测到亚硝酸（HONO）
The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium
摘要：
氮氧化物被认为作为氮库发挥重要作用，并可能参与形成更复杂的物种。到目前为止，在星际介质中只探测到NO、$_2$ O和HNO。我们报告了第一次星际探测到亚硝酸（HONO）。利用阿塔卡马大型毫米/亚毫米波天线阵在低质量原恒星双星IRAS~16293--2422的B分量方向上发现了12条谱线，它们位于NO和N $_2$ O的位置。局部热力学平衡模型用于推导该分子的柱密度（在0.5“束中的$\sim$ 9 $\times$ 10 $^{14}$ cm $^{-2}$）和激发温度（$\sim$ 100 K）。还在数据中检索了HNO、NO $_2$、NO $^+$和HNO $_3$，但未检出。我们使用更新版本的化学代码Nautilus模拟了HONO形成，并将结果与观测结果进行了比较。化学模型能够满意地再现HONO、N $_2$ O和NO $_2$的丰度，但不能再现NO、HNO和NH $_2$ OH的丰度。这可能是由于某些热解吸机制是破坏性的，因此限制了气相中存在的HNO和NH $_2$ OH的量。其他的选择是这些物种在冰中的紫外线光破坏或在原恒星温度下可能相关的缺失反应。
英文摘要：
Nitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in the formation of more complex species. Until now, only NO, N$_2$O and HNO have been detected in the interstellar medium. We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component B of the low-mass protostellar binary IRAS~16293--2422 with the Atacama Large Millimeter/submillimeter Array, at the position where NO and N$_2$O have previously been seen. A local thermodynamic equilibrium model was used to derive the column density ($\sim$ 9 $\times$ 10$^{14}$ cm$^{-2}$ in a 0.5'' beam) and excitation temperature ($\sim$ 100 K) of this molecule. HNO, NO$_2$, NO$^+$, and HNO$_3$ were also searched for in the data, but not detected. We simulated the HONO formation using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical model is able to reproduce satisfactorily the HONO, N$_2$O, and NO$_2$ abundances, but not the NO, HNO, and NH$_2$OH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NH$_2$OH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures.
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