Phase transitions in benzene under dynamic and static compression,Journal of Raman Spectroscopy

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Phase transitions in benzene under dynamic and static compression
Journal of Raman Spectroscopy ( IF 2.4 ) Pub Date : 2020-11-24 , DOI: 10.1002/jrs.6047
Usha Rao _{1,

2} , S. Chaurasia _{1,

3} , Ajay K. Mishra _{1,

3} , John Pasley ₄

Affiliation

Phase transitions in liquid benzene under laser shocked conditions are studied using high‐resolution time‐resolved Raman spectroscopic technique. The C‐C ring breathing mode (υ₁) of benzene at 993 cm⁻¹ is analyzed to monitor the phase transitions occurring in the Raman spectra during shock wave propagation in the pressure range 1.3–5 GPa. Phase transition from liquid benzene to solid benzene (Phase I) is observed below 1.3 GPa, and above this pressure, another phase transition from Phases I and II occurs. We also performed Raman spectroscopic measurements under static compression employing diamond anvil cell (DAC) to compare the effect of shock wave on benzene with isothermal compression using DAC. In static pressure measurements, the first phase transition from liquid to solid benzene (orthorhombic) occurs at 0.3 GPa, and the second phase transition from benzene I (orthorhombic) to benzene Phase II (monoclinic) occurs at 2.3 GPa, which is higher than that observed in case of shock compression experiments. The observed high‐resolution spectrum enables us to determine the effect of pressure gradient upon the Raman spectrum of benzene in shocked condition. One‐dimensional radiation‐hydrodynamic simulations were performed to corroborate the Raman spectroscopic results under dynamic compression. Simulated spatial profiles of the shock wave propagation in benzene at different delay times are used to explain the observation of multiple Raman modes in the spectral region 990–1020 cm⁻¹. It is understood that different regions of the sample experience distinct pressure due to shock pressure gradient across the sample. The new Raman modes appearing in this spectral region are attributed to the Raman signals due to phase transition and from differently shocked regions of benzene under dynamic compression. The effect of reflected shock wave from benzene‐glass interface manifested in terms of red shifting and intensity enhancement of Raman modes at higher pressure is explained in this study.

中文翻译：

苯在动态和静态压缩下的相变

使用高分辨率时间分辨拉曼光谱技术研究了激光冲击条件下液态苯中的相变。的C-C环呼吸模式（υ ₁苯）在993厘米^-1分析以监测在1.3-5 GPa压力范围内冲击波传播期间拉曼光谱中发生的相变。在1.3 GPa以下观察到从液态苯到固态苯的相变（阶段I），而在该压力以上，则发生了相I和相II的另一相变。我们还使用金刚石砧盒（DAC）在静态压缩下进行了拉曼光谱测量，以比较冲击波对苯的冲击波与使用DAC的等温压缩的影响。在静压测量中，从液相苯到固态苯（斜方苯）的第一相转变发生在0.3 GPa，从苯Ⅰ（斜方苯）到苯第二相（单斜）的第二相转变发生在2.3 GPa，高于在冲击压缩实验中观察到。观察到的高分辨率光谱使我们能够确定压力梯度对冲击条件下苯的拉曼光谱的影响。进行了一维辐射-流体动力学模拟，以证实在动态压缩下的拉曼光谱结果。冲击波在不同延迟时间下在苯中传播的模拟空间轮廓用于解释在990-1020 cm光谱区域内多个拉曼模式的观察^-1。应当理解，由于样品上的冲击压力梯度，样品的不同区域经受不同的压力。出现在该光谱区域的新拉曼模式归因于相变引起的拉曼信号，并且来自在动态压缩下苯的不同受激区域。本研究解释了苯玻璃界面反射冲击波在较高压力下表现为红移和拉曼模强度增强的影响。

更新日期：2020-11-24

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