Interstellar detection and chemical modeling of iso-propanol and its normal isomer
Interstellar detection and chemical modeling of iso-propanol and its normal isomer
复制标题
异丙醇及其正异构体的星际探测和化学建模
DOI：
10.1051/0004-6361/202243575
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发表时间：
2022
影响因子：
6.5
通讯作者：
Menten, K. M.
中科院分区：
文献类型：
--
作者：
Belloche, A.;Garrod, R. T.;Zingsheim, O.;Müller, H. S.;Menten, K. M.
背景阿塔卡马大毫米/亚毫米阵列(ALMA)的出现允许在高质量恒星形成的原始星团射手座(SGR)B2(N)中探测到分支烷基分子，揭示了星际化学的一个新维度。天体化学模拟随后预测，除了一定程度的分子复杂性外，支化分子甚至可以主宰其直链异构体。目的更广泛地，我们的目标是通过在初级或次级碳原子上连接一个官能团，进一步探索星际介质中存在的具有正常和异构体能力的复杂有机分子。方法我们利用ALMA在高角分辨率下进行的成像光谱线测量ReMoCA和最近对丙醇的光谱研究的结果，在热分子核SGR B2(N2)中寻找该分子的异构体和正异构体。在局部热力学平衡的假设下，对干涉光谱进行了分析。我们扩展了天体化学模型Magickal的网络，以探索丙醇的形成途径，并将观测结果置于更广泛的天体化学背景中。结果我们首次在星际探测到异丙醇-β-C3H7OH，其位置位于SGR B2(N2)的一个窄线宽位置。我们还报道了第一次在热核中安全地检测到丙醇的正常异构体n-C3H7OH。异丙醇的丰度比接近正丙醇，丰度比为0.6，这与我们以前在较低的角分辨率下在SGR B2(N_2)中获得的异丙基氰化物和正丙基氰化物的丰度比0.4相似，我们之前的ALMA测量EMoCA。观测结果与天体化学模型的结果很好地吻合，表明尘粒冰盖中的丙烯在水光解离的驱动下发生OH-自由基加成反应，可以生成适量的正丙醇和异丙醇。结论正丙醇和异丙醇的检测及其比值表明，在相似大小的星际分子中，对丙基氰化物正态形式的适度偏好可能是更普遍的特征。检测其他星际有机分子的官能团附着在伯碳或次碳上，可能有助于确定决定它们正常与iso比率的主要过程。丁醇及其异构体将是酒精家族下一个明显的候选者，但它们在高温岩心中的检测将是具有挑战性的。
ContextThe detection of a branched alkyl molecule in the high-mass star forming protocluster Sagittarius (Sgr) B2(N) permitted by the advent of the Atacama Large Millimeter/submillimeter Array (ALMA) revealed a new dimension of interstellar chemistry. Astrochemical simulations subsequently predicted that beyond a certain degree of molecular complexity, branched molecules could even dominate over their straight-chain isomers.AimsMore generally, we aim to probe further the presence in the interstellar medium of complex organic molecules with the capacity to exhibit both a normal and iso form, via the attachment of a functional group to either a primary or secondary carbon atom.MethodsWe used the imaging spectral line survey ReMoCA performed with ALMA at high angular resolution and the results of a recent spectroscopic study of propanol to search for the iso and normal isomers of this molecule in the hot molecular core Sgr B2(N2). We analyzed the interferometric spectra under the assumption of local thermodynamical equilibrium. We expanded the network of the astrochemical model MAGICKAL to explore the formation routes of propanol and put the observational results in a broader astrochemical context.ResultsWe report the first interstellar detection of iso-propanol, ¿-C3H7OH, toward a position of Sgr B2(N2) that shows narrow linewidths. We also report the first secure detection of the normal isomer of propanol, n-C3H7OH, in a hot core. Iso-propanol is found to be nearly as abundant as normal-propanol, with an abundance ratio of 0.6 which is similar to the ratio of 0.4 that we obtained previously for iso- and normal-propyl cyanide in Sgr B2(N2) at lower angular resolution with our previous ALMA survey, EMoCA. The observational results are in good agreement with the outcomes of our astrochemical models, which indicate that the OH-radical addition to propylene in dust-grain ice mantles, driven by water photodissociation, can produce appropriate quantities of normal- and iso-propanol. The normal-to-iso ratio in Sgr B2(N2) may be a direct inheritance of the branching ratio of this reaction process.ConclusionsThe detection of normal- and iso-propanol and their ratio indicate that the modest preference for the normal form of propyl cyanide determined previously may be a more general feature among similarly sized interstellar molecules. Detecting other pairs of interstellar organic molecules with a functional group attached either to a primary or secondary carbon may help in pinning down the processes that dominate in setting their normal-to-iso ratios. Butanol and its isomers would be the next obvious candidates in the alcohol family, but their detection in hot cores will be challenging.