Raman studies of solvent- and solute-molecule states in supercritical fluids

本工作旨在利用拉曼光谱同时研究超临界流体中溶剂和溶质的分子状态，以便更好地理解多组分超临界流体中的溶剂化。第一年，我们搭建了高压系统，改进了光学系统。第二年，我们对这些体系的性能进行了详细的测试，并对CO_2/苯和CO_2/氯苯二元样品进行了拉曼研究。对于高压系统的操作条件，我们认为以下方式是实现所需样品条件的最佳方式。也就是说，我们首先在恒定的温度和压力下，将溶剂和溶质流体以给定的流速引入拉曼细胞。当一段时间后溶质的浓度确定后，我们在拉曼测量时关闭了电池的进出口。在此之后，我们通过每次通过出口释放细胞内的内容物来降低细胞压力来重复测量。通过对初步测量结果的分析，我们得到了以下结果：(a)即使在溶质摩尔分数为0.01的样品中，我们也能获得足够质量的拉曼光谱；(b)当CO_2/苯的流量比为1:0.1时，我们发现在超临界态的类气区出现了额外的拉曼光谱。c当CO_2/氯苯的流量比为2:0.01时，我们发现氯苯的条带有明显的位移和带宽变化，这可能是具有偶极矩的溶质分子与CO_2之间的特定相互作用。

This work aimed at studying simultaneously the molecular states of both the solvent and solute in supercritical fluids by Raman spectroscopy for the better understanding of solvation in multi-components supercritical fluids. In the first year, we constructed the high-pressure system and improved the optical system. In the second year, we checked the performance of these systems in detail and carried out Raman studies on CO_2/benzene and CO_2/chlorobenzene binary samples.As to the operation condition of the high-pressure system, we concluded that the following manner is the best for realizing desired sample conditions. Namely, we first introduce into the Raman cell, at a constant temperature and a constant pressure, the solvent and solute fluids with a given flow rates. When the concentration of the solute was established after a certain period, we close the inlet and outlet of the cell during the Raman measurement. After this we repeat the measurement by reducing the cell pressure every time by releasing the content in the cell through the outlet.By the analysis of the preliminary measurements, we have obtained the following results, (a) We can obtain Raman spectra with sufficient quality even for the sample with 0.01 mole fraction of the solute, (b) With a CO_2/benzene sample of the 1:0.1 flow-rate ratio, we found additional Raman bands which appear in the gas-like region of the supercritical state. These bands are considered to be attributed the complex molecule between CO_2 and benzene, are worth being studied further in detail, c With a CO_2/chlorobenzene sample of the 2:0.01 flow-rate ratio, we found a remarkable shift and bandwidth change of the chlorobenzene bands, which is considered to indicate the specific interaction between solute molecules with dipole moment and CO_2.