Elettra L. Piacentino, Aurelia Balkanski, Mahesh Rajappan and Karin I. Öberg
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引用次数: 0
摘要
芳香族结构是 RNA 和代谢物等关键生物分子的基础,因此年轻行星上芳香族分子的丰度备受关注。最近在星际云和彗星中探测到的苯甲腈和其他芳香族化合物揭示了丰富的芳香族天体化学。在恒星和行星形成的寒冷阶段,这些芳香族分子很可能大多存在于冰粒外壳中,可以通过红外光谱对它们进行观测。我们展示了苯和四种单取代苯分子--甲苯、苯酚、苯甲腈和苯甲醛--的实验室红外光谱,以确定它们在未稀释的芳香冰以及与水和 CO 的混合物中的红外冰吸收率。我们还利用温度编程解吸实验确定了芳香族冰解吸速率的特征,并提取了结合能和各自的预指数。我们利用这些来预测这些分子在原恒星和原行星盘的什么温度下升华为气相。我们发现苯和单取代苯衍生物的结合能在 5220-8390 K(43-70 kJ mol-1)范围内,属于低挥发性物质,这表明苯和官能化芳香分子的大部分化学反应预计会在恒星和行星形成过程中的冰相发生。
Aromatic structures are fundamental for key biological molecules such as RNA and metabolites and the abundances of aromatic molecules on young planets are therefore of high interest. Recent detections of benzonitrile and other aromatic compounds in interstellar clouds and comets have revealed a rich aromatic astrochemistry. In the cold phases of star and planet formation, most of these aromatic molecules are likely to reside in icy grain mantles, where they could be observed through IR spectroscopy. We present laboratory IR spectra of benzene and four monosubstituted benzene molecules—toluene, phenol, benzonitrile, and benzaldehyde—to determine their IR ice absorbances in undiluted aromatic ices, and in mixtures with water and CO. We also characterize the aromatic ice desorption rates, and extract binding energies and respective pre-exponential factors using temperature-programmed desorption experiments. We use these to predict at which protostellar and protoplanetary disk temperatures these molecules sublimate into the gas phase. We find that benzene and monosubstituted benzene derivatives are low-volatility with binding energies in the 5220–8390 K (43–70 kJ mol−1) range, which suggests that most of the chemistry of benzene and of functionalized aromatic molecules is to be expected to occur in the ice phase during star and planet formation.