Relationship between Raman spectral features and fugacity in mixtures of gases
Relationship between Raman spectral features and fugacity in mixtures of gases
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DOI：
10.1002/jrs.5304
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发表时间：
2018-03-01
影响因子：
2.5
通讯作者：
Bodnar, Robert J.
中科院分区：
文献类型：
--
作者：
Lamadrid, Hector M.;Steele-MacInnis, Matthew;Bodnar, Robert J.
拉曼光谱产生关于共价键合分子的内部振动模式的信息，其对局部分子环境敏感。因此，在不同温度和/或压力下收集的由共价键合的分子组成的气体的拉曼光谱显示带位置和其他光谱特征的变化，反映了与局部物理和化学环境相关的气体颗粒之间的分子尺度相互作用（吸引和排斥）。由于分子间的相互作用，气体是非理想的，逸度是描述气体分压的基本热力学量，经过调整以解释非理想性。物质的逸度通常是通过热力学计算而不是直接分析或测量获得的，因此在概念上是模糊的。在这里，我们进行光谱分析的气体混合物的已知组成的可变和已知的压力和耦合这些结果与热力学计算的气体逸度。我们表明，气体混合物中的拉曼峰位移直接相关的组分气体物种的逸度。因此，我们的研究结果提供了实验证据，气体的逸度可以估计从现场收集的拉曼光谱。通过这种方法，热力学量逸度和相关的热力学性质活动直接与潜在的分子尺度现象，根据分子物种的振动特性。这代表了一种易于处理的方法，有效地获得大型数据集的气体混合物的热力学性质，并与一些调整，可能会导致一个可行的方法，为其他物质，如结晶固溶体，水离子和电解质的非理想的混合规则。
Raman spectroscopy yields information about the internal vibrational modes of covalently bonded molecules, which are sensitive to the local molecular environment. As such, Raman spectra of a gas composed of covalently bonded molecules collected at different temperatures and/or pressures show variations in band positions and other spectral features, reflecting molecular-scale interactions (attraction and repulsion) among gas particles associated with the local physical and chemical environment. Because the molecules interact, gases are nonideal, and fugacity is the fundamental thermodynamic quantity that describes partial pressures of gases, adjusted to account for the nonideality. The fugacity of a substance is generally obtained from thermodynamic calculations rather than by direct analysis or measurement and, as such, is conceptually nebulous. Here, we perform spectroscopic analyses of a gas mixture of known composition at variable and known pressures and couple these results with thermodynamic calculations of gas fugacities. We show that Raman peak shifts in gas mixtures are directly correlated to fugacities of the component gas species. Our results thus provide experimental evidence that fugacities of gases can be estimated from Raman spectra collected in situ. By this approach, the thermodynamic quantities fugacity and the related thermodynamic property activity are linked directly with underlying molecular-scale phenomena, according to the vibrational properties of molecular species. This represents a tractable method to efficiently obtain large datasets on thermodynamic properties of gas mixtures, and with some adjustments, may lead to a viable method for developing nonideal mixing rules for other substances, such as crystalline solid solutions, aqueous ions, and electrolytes.