Millimeter wave spectrum and search for vinyl isocyanate toward Sgr B2(N) with ALMA
Millimeter wave spectrum and search for vinyl isocyanate toward Sgr B2(N) with ALMA
复制标题
使用 ALMA 进行毫米波谱并搜索 Sgr B2(N) 的异氰酸乙烯酯
DOI：
10.1051/0004-6361/202243627
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发表时间：
2022
影响因子：
6.5
通讯作者：
Müller, H. S.
中科院分区：
文献类型：
--
作者：
Vávra, K.;Kolesniková, L.;Belloche, A.;Garrod, R. T.;Koucký, J.;Uhlíková, T.;Luková, K.;Guillemin, J.-C.;Kania, P.;Müller, H. S.
对异氰酸（HNCO）、异氰酸甲酯（CH3NCO）和最近的异氰酸乙酯（C2H5NCO）的星际探测引发了一个问题：在星际介质中是否可以探测到异氰酸乙烯酯（C2H3NCO）。在文献中只有低频光谱数据（<40 GHz）可用于该物种，这使得在较高频率下的预测相当不确定，这反过来又阻碍了使用毫米波天文学在空间中搜索该分子。第一次，它的存在下，在高质量的恒星形成区域Sgr B2，在那里其他异氰酸酯和过多的复杂的有机分子observed.MethodsWe记录的纯旋转光谱的乙烯基异氰酸酯在频率区域127.5 - 218和285 - 330 GHz的使用布拉格毫米波光谱仪。光谱分析得到了高级量子化学计算的支持。在天文学方面，我们假设局部热力学平衡来计算乙烯基异氰酸酯的合成光谱，并在阿塔卡马大型毫米/亚毫米阵列（阿尔马）对高质量恒星形成原星团Sgr B2（N）进行的ReMoCA调查中寻找它。此外，我们寻找相关的分子乙基异氰酸酯在同一source.ResultsThe旋转和离心畸变常数的准确值的反式和顺式乙烯基异氰酸酯的基态振动状态的分析超过1000个转换。我们报告未检测到乙烯基和乙基异氰酸酯对Sgr B2（N）的主要热核心。我们发现，乙烯基和乙基异氰酸酯是至少11和3倍少丰富的甲基异氰酸酯在此source.ConclusionsAlthough星际甲基异氰酸酯本身的精确形成机制仍然不确定，我们推断，从现有的天体化学模型，我们的观测上限为CH3NCO：Sgr B2（N）中的C2H5NCO比例与通过从异氰酸甲酯中提取或光解离H原子在尘粒上形成的异氰酸乙酯一致，然后加入甲基。这种用于异氰酸乙酯生产的方法的优势，结合不存在用于异氰酸乙烯酯的类似机理，将表明比率C2H3NCO：C2H5NCO应小于1。尽管在Sgr B2（N）中没有检测到乙烯基异氰酸酯，但这项工作的结果代表了对先前低频研究的重大改进，并将有助于天文学界继续在宇宙中寻找这种物种。
ContextThe interstellar detections of isocyanic acid (HNCO), methyl isocyanate (CH3NCO), and very recently also ethyl isocyanate (C2H5NCO) invite the question of whether or not vinyl isocyanate (C2H3NCO) can be detected in the interstellar medium. There are only low-frequency spectroscopic data (<40 GHz) available for this species in the literature, which makes predictions at higher frequencies rather uncertain, which in turn hampers searches for this molecule in space using millimeter (mm) wave astronomy.AimsThe aim of the present study is on one hand to extend the laboratory rotational spectrum of vinyl isocyanate to the mm wave region and on the other to search, for the first time, for its presence in the high-mass star-forming region Sgr B2, where other isocyanates and a plethora of complex organic molecules are observed.MethodsWe recorded the pure rotational spectrum of vinyl isocyanate in the frequency regions 127.5–218 and 285–330 GHz using the Prague mm wave spectrometer. The spectral analysis was supported by high-level quantum-chemical calculations. On the astronomy side, we assumed local thermodynamic equilibrium to compute synthetic spectra of vinyl isocyanate and to search for it in the ReMoCA survey performed with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming protocluster Sgr B2(N). Additionally, we searched for the related molecule ethyl isocyanate in the same source.ResultsAccurate values for the rotational and centrifugal distortion constants are reported for the ground vibrational states of trans and cis vinyl isocyanate from the analysis of more than 1000 transitions. We report nondetections of vinyl and ethyl isocyanate toward the main hot core of Sgr B2(N). We find that vinyl and ethyl isocyanate are at least 11 and 3 times less abundant than methyl isocyanate in this source, respectively.ConclusionsAlthough the precise formation mechanism of interstellar methyl isocyanate itself remains uncertain, we infer from existing astrochemical models that our observational upper limit for the CH3NCO:C2H5NCO ratio in Sgr B2(N) is consistent with ethyl isocyanate being formed on dust grains via the abstraction or photodissociation of an H atom from methyl isocyanate, followed by the addition of a methyl radical. The dominance of such a process for ethyl isocyanate production, combined with the absence of an analogous mechanism for vinyl isocyanate, would indicate that the ratio C2H3NCO:C2H5NCO should be less than unity. Even though vinyl isocyanate was not detected toward Sgr B2(N), the results of this work represent a significant improvement on previous low-frequency studies and will help the astronomical community to continue searching for this species in the Universe.