Behavior of Long-Chain Hydrocarbons at High Pressures and Temperatures
Behavior of Long-Chain Hydrocarbons at High Pressures and Temperatures
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DOI：
10.1021/acs.jpcb.1c10786
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发表时间：
2022-04-07
影响因子：
3.3
通讯作者：
Boehler, Reinhard
中科院分区：
文献类型：
--
作者：
Basu, Abhisek;Mookherjee, Mainak;Boehler, Reinhard
尽管陨石中记录了长链脂肪族碳氢化合物，但人们对其来源知之甚少。一个关键的问题是，它们是原始的还是陆地变化的副产品？为了了解这些长链碳氢化合物是否为本土碳氢化合物，重要的是要探讨它们在进入和通过大气层期间外星物体所经历的条件下的热力学和机械稳定性。陨石经历的极端压力和温度可能会改变这些长链碳氢化合物的分子组织。这些与极端条件相关的结构变化通常通过实验室的拉曼光谱测量来记录下来。到目前为止，拉曼光谱测量已经研究了静态压缩对脂肪烃的影响。温度对结构变化的影响还没有得到很好的研究。为了弥补这一差距，在这项研究中，我们探索了两种脂肪族碳氢化合物在同时高压和高温下的行为。我们已经使用了一个电阻加热的钻石砧座电池。关于压缩到中等压力，在低能区出现新的振动模式证实了先前的研究，并与线性链的弯曲有关。当加热到接近220摄氏度时，我们注意到新的低能量模式经历了软化。模式软化可能是由于烷烃链的不弯曲和模式的非谐性的共同作用。
Although long-chain aliphatic hydrocarbons are documented in meteorites, their origin is poorly understood. A key question is whether they are pristine or a byproduct of terrestrial alteration? To understand if these long-chain hydrocarbons are indigenous, it will be important to explore their thermodynamic and mechanical stability at conditions experienced by extraterrestrial objects during atmospheric entry and passage. Extreme pressures and temperatures experienced by meteorites are likely to alter the molecular organization of these long-chain hydrocarbons. These structural changes associated with extreme conditions are often documented via laboratory-based Raman spectroscopic measurements. So far, Raman spectroscopic measurements have investigated the effect of static compression on the aliphatic hydrocarbons. The effect of temperature on the structural changes remains poorly explored. To bridge this gap, in this study, we have explored the behavior of two aliphatic hydrocarbons at simultaneously high pressures and temperatures. We have used a resistively heated diamond anvil cell. On compression to moderate pressures, the appearance of new vibrational modes in the low-energy region confirms prior studies and is related to the bending of the linear chains. Upon heating to similar to 220 degrees C, we note that the new low-energy mode undergoes softening. The mode softening is likely due to the combination of unbending of the alkane chain and mode anharmonicity.