Spectroscopic Investigation of the High-Pressure Behavior of Aliphatic Hydrocarbon: Implications for Planetary Processes
Spectroscopic Investigation of the High-Pressure Behavior of Aliphatic Hydrocarbon: Implications for Planetary Processes
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DOI：
10.1021/acsearthspacechem.0c00259
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发表时间：
2021-02-10
影响因子：
3.4
通讯作者：
Boehler, Reinhard
中科院分区：
文献类型：
--
作者：
Basu, Abhisek;Mookherjee, Mainak;Boehler, Reinhard
十八烷（C18H38）是一种富含碳质球粒陨石的脂肪族烃。在陨石中发现的这些碳氢化合物是原始的，还是在这些陨石被送到地球时发生了随后的变化，这是有争议的。众所周知，陨石在进入地球大气层时经常受到极端的压力和温度。为了探索十八烷在高压下的行为，即其分子结构对压缩的反应，我们将金刚石砧细胞与拉曼光谱结合使用。我们发现，在室温下，当压缩到5gpa时，线性链十八烷分子转变为弯曲链构型。在其他碳氢化合物中也有类似的从线性结构到弯曲结构的转变。我们发现从线性构型到弯曲构型的转变压力与烷烃的链长呈线性相关，即链长越长，在压缩下线性构型的烷烃稳定性越差。这些弯链构型中的扭结可能是长链烃解离成小链烃的位点。本研究中检测的十八烷样品没有经历任何额外的过渡到本研究中探索的最高压力（类似于18gpa）。
Octadecane (C18H38) is an aliphatic hydrocarbon that is abundant in carbonaceous chondritic meteorites. It is debated whether these hydrocarbons found in the meteorite are pristine or are a result of subsequent modifications as these meteorites are delivered to the Earth. It is well-known that meteorites are often subjected to extreme pressures and temperatures upon entering the Earth's atmosphere. To explore the behavior of octadecane at high pressures, that is, how its molecular structure responds to compression, we use a diamond anvil cell in conjunction with Raman spectroscopy. We find that at room temperatures, upon compression to similar to 5 GPa, a linear-chain octadecane molecule transforms into a bent-chain configuration. Similar transitions from linear to a bent configuration in other hydrocarbons have been documented. We find a linear correlation between the transition pressure from linear to bent configuration, and the chain length of the alkane, that is, longer chain lengths, is likely to be less stable in the linear configuration under compression. These kinks in the bent-chain configuration are likely sites for the dissociation of the longer chain hydrocarbons to smaller hydrocarbons. The octadecane sample examined in this study did not undergo any additional transition to the highest pressure (similar to 18 GPa) explored in this study.