Modeling carbon chain anions in L1527
Modeling carbon chain anions in L1527
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DOI：
10.1086/590468
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发表时间：
2008-09-20
影响因子：
4.9
通讯作者：
Herbst, Eric
中科院分区：
文献类型：
--
作者：
Harada, Nanase;Herbst, Eric
低质量原恒星区域L1527是不寻常的，因为它含有可观察到的丰富的不饱和碳链分子，包括CnH自由基、H2Cn碳烯、氰聚乙烯和负离子C4H-和C6H-，所有这些都与冷核的关系比与原恒星区域的关系更密切。Sakai等人认为，这些分子是在L1527中由化学前体甲烷形成的，甲烷在该地区升温期间从颗粒中蒸发出来。随着osu.03.2008气相网络扩展到包括C-n（-）和CnH-家族的负离子，以及新检测到的C3N-，我们模拟了甲烷在温度接近25-30 K时蒸发后发生的化学反应。我们能够在大约5 x 10(3)年的时间内重现L1527中观察到的大部分分子丰度。在较晚的时间内，阴离子的总体丰度大于电子的总体丰度，这对许多有机物种和离子有影响。在我们的计算中，阴离子与中性的比值与C6H-的观测值很好地吻合，但C4H-的阴离子与中性的比值比观测值高出3个数量级以上。为了解释这种差异，需要进一步研究电子附着和其他阴离子反应的速率系数。
The low-mass protostellar region L1527 is unusual because it contains observable abundances of unsaturated carbon-chain molecules including CnH radicals, H2Cn carbenes, cyanopolyynes, and the negative ions C4H- and C6H-, all of which are more associated with cold cores than with protostellar regions. Sakai et al. suggested that these molecules are formed in L1527 from the chemical precursor methane, which evaporates from the grains during the heat-up of the region. With the gas-phase osu.03.2008 network extended to include negative ions of the families C-n(-), and CnH-, as well as the newly detected C3N-, we modeled the chemistry that occurs following methane evaporation at T approximate to 25-30 K. We are able to reproduce most of the observed molecular abundances in L1527 at a time of approximate to 5 x 10(3) yr. At later times, the overall abundance of anions become greater than that of electrons, which has an impact on many organic species and ions. The anion-to-neutral ratio in our calculation is in good agreement with observation for C6H-, but exceeds the observed ratio by more than 3 orders of magnitude for C4H-. In order to explain this difference, further investigation is needed on the rate coefficients for electron attachment and other reactions regarding anions.