Solvation Structures of cis- and trans-1,2-Dichloroethylene in Supercritical CO2 Investigated by Raman Spectroscopy and Attractive Energy Calculations
Solvation Structures of cis- and trans-1,2-Dichloroethylene in Supercritical CO2 Investigated by Raman Spectroscopy and Attractive Energy Calculations
复制标题
DOI：
10.1021/jp903240v
复制
发表时间：
2009-10-08
影响因子：
3.3
通讯作者：
Saitow, Ken-ichi
中科院分区：
文献类型：
--
作者：
Kajiya, Daisuke;Saitow, Ken-ichi
测量了顺式和反式1，2-二氯乙烯（C2 H2 Cl 2）在超临界二氧化碳（CO2）中C=C伸缩振动模式的振动拉曼光谱。通过将流体密度改变20倍，在固定的溶质摩尔分数下收集光谱。随着密度的增加，C=C伸缩模式的峰值频率移向低能量侧的等温线降低的温度，T-r = T/T-c = 1.02，1.06，和1.20。利用微扰硬球理论分析了这些密度依赖性，将位移分解为吸引分量和排斥分量。cis-C2 H2 Cl 2的排斥位移几乎与trans-C2 H2 Cl 2的排斥位移相当。然而，非极性的反式-C2 H2 Cl 2的吸引力的位移显着大于极性的顺式-C2 H2 Cl 2在所有的密度和温度。为了评估异构体的差异，我们计算了每个异构体的C=C伸缩模式的吸引力位移，包括溶质C2 H2 Cl 2和溶剂CO2分子之间的色散，偶极诱导偶极和偶极-四极相互作用。通过考虑分子构型和取向对这三种相互作用进行了量化，并通过3D示意图阐明了异构体周围的溶剂化结构。结果表明，在超临界CO2中，trans-C2 H2 Cl 2周围的各向异性溶剂化结构是导致较大吸引位移的原因。异构体之间的溶剂化结构的差异是显着的，在Tr = 1.02，但变得较小的温度升高到T-r = 1.20。
Vibrational Raman spectra of the C=C stretching modes of cis- and trans-1,2-dichloroethylene (C2H2Cl2) were measured in supercritical carbon dioxide (CO2). The spectra were collected at a fixed solute mole fraction by varying the fluid density by a factor of 20. As the density increased, the peak frequencies of the C=C stretching modes shifted toward the low-energy side at isotherms of reduced temperature, T-r = T/T-c = 1.02, 1.06, and 1.20. By analyzing these density dependences using the perturbed hard-sphere theory, we decomposed the shifts into attractive and repulsive Components. The repulsive shifts of cis-C2H2Cl2 were almost equivalent to those of trans-C2H2Cl2. However, the attractive shifts of nonpolar trans-C2H2Cl2 were significantly greater than those of polar cis-C2H2Cl2 at all densities and temperatures. To evaluate the difference in the isomers, we calculated the attractive shifts of the C=C stretching modes of each isomer, composing of dispersion, dipole-induced-dipole, and dipole-quadrupole interactions between solute C2H2Cl2 and solvent CO2 molecules. These three interactions were quantified by considering molecular configurations and orientations, and solvation structures around the isomers were elucidated by 3D schematic diagrams. As a result, it was shown that the anisotropic solvation structure around trans-C2H2Cl2 was responsible for the larger attractive shifts ill the supercritical CO2. The difference of solvation structures between the isomers was significant at Tr = 1.02 but became minor as the temperature increased to T-r = 1.20.