arXiv 1609.025702016-09-08astro-ph.GA

未检测到HC $_{11}$ N向TMC-1转化：限制大碳链分子的化学性质

Non-Detection of HC$_{11}$N toward TMC-1: Constraining the Chemistry of Large Carbon-Chain Molecules

Ryan A. Loomis, Christopher N. Shingledecker, Glen Langston, Brett A. McGuire, Niklaus M. Dollhopf, Andrew M. Burkhardt, Joanna Corby, Shawn T. Booth, P. Brando… 展开作者

Ryan A. Loomis, Christopher N. Shingledecker, Glen Langston, Brett A. McGuire, Niklaus M. Dollhopf, Andrew M. Burkhardt, Joanna Corby, Shawn T. Booth, P. Brandon Carroll, Barry Turner, Anthony J. Remijan

备注：: 10 pages, 7 figures, 3 tables, accepted for publication in MNRAS
DOI：: 10.1093/mnras/stw2302

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摘要：

Bell等人（1997年）报告说，在冷暗云TMC-1中首次探测到氰基多炔HC $_{11}$ N;此后没有任何关于探测到任何来源的报告。氰基多炔和其他碳链分子对TMC-1的额外观察显示了分子大小和柱密度之间的对数线性趋势，并且为了进一步探索驱动这种趋势的潜在化学过程，我们分析了HC $_9$ N和HC $_{11}$ N对TMC-1的GBT观察。虽然我们发现HC $_9$ N柱密度与先前值一致，但未检测到HC $_{11}$ N，我们推导出的柱密度上限显著低于Bell等人报告的值。使用最先进的化学模型，我们研究了柱密度趋势中非线性的可能解释。尽管更新了化学模型，以更好地解释离子-偶极相互作用，我们无法解释HC $_{11}$ N的未检测，我们将其解释为以前未知的碳链化学的证据。我们认为环化反应可能是导致HC $_{11}$ N丰度耗尽的原因，并且这些环化反应的产物应作为候选星际分子进行研究。

英文摘要：

Bell et al. (1997) reported the first detection of the cyanopolyyne HC$_{11}$N toward the cold dark cloud TMC-1; no subsequent detections have been reported toward any source. Additional observations of cyanopolyynes and other carbon-chain molecules toward TMC-1 have shown a log-linear trend between molecule size and column density, and in an effort to further explore the underlying chemical processes driving this trend, we have analyzed GBT observations of HC$_9$N and HC$_{11}$N toward TMC-1. Although we find an HC$_9$N column density consistent with previous values, HC$_{11}$N is not detected and we derive an upper limit column density significantly below that reported in Bell et al. Using a state-of-the-art chemical model, we have investigated possible explanations of non-linearity in the column density trend. Despite updating the chemical model to better account for ion-dipole interactions, we are not able to explain the non-detection of HC$_{11}$N, and we interpret this as evidence of previously unknown carbon-chain chemistry. We propose that cyclization reactions may be responsible for the depleted HC$_{11}$N abundance, and that products of these cyclization reactions should be investigated as candidate interstellar molecules.

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