Department of Chemistry, University of Minnesota-Twin Cities , 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States.
J Phys Chem B. 2013 Dec 12;117(49):15741-9. doi: 10.1021/jp4064627. Epub 2013 Sep 24.
Linear absorption spectroscopy of the iridium-bound carbonyl on an iodated adduct of Vaska's complex has shown that the mean vibrational frequency is insensitive to solvation by a broad range of solvents, while the spectral line width changes significantly. The spectral broadening is more significant in chloroform than benzyl alcohol, which is puzzling considering that benzyl alcohol is more polar. In this study, 2D-IR spectroscopy was performed on this vibrational mode to dissect the linear line shape into its homogeneous and inhomogeneous contributions in binary solvent mixtures of either chloroform or benzyl alcohol in d6-benzene. The full frequency-frequency correlation function was determined, including the homogeneous line width and fast spectral diffusion. We find that the frequency fluctuation magnitudes show the most notable changes in chloroform mixtures, while the time constants for spectral diffusion change more dramatically in benzyl alcohol mixtures. Nonetheless, we conclude that the frequency fluctuation magnitudes in both solvent mixtures most clearly explain the differences in their linear line widths. The homogeneous contributions were found to either stay the same or decrease as the more polar solvent was added to d6-benzene, thereby implicating inhomogeneous dynamics as the dominant broadening mechanism.
对 Vaska 配合物碘化物加合物中铱结合羰基的线性吸收光谱研究表明，平均振动频率对溶剂的影响不敏感，而光谱线宽变化显著。与苄醇相比，氯仿中的光谱展宽更为显著，这令人费解，因为苄醇的极性更大。在这项研究中，我们在这个振动模式上进行了二维红外光谱（2D-IR）实验，以将线性线形状分解为二氯甲烷或苄醇在氘代苯中的二元溶剂混合物中的均匀和非均匀贡献。确定了完整的频-频相关函数，包括均匀线宽和快速光谱扩散。我们发现，在氯仿混合物中，频率波动幅度变化最显著，而在苄醇混合物中，光谱扩散的时间常数变化更为剧烈。尽管如此，我们得出的结论是，在这两种溶剂混合物中，频率波动幅度最能清楚地解释它们的线性线宽差异。发现均匀贡献要么保持不变，要么随着更极性溶剂加入到氘代苯中而减小，从而暗示非均匀动力学是主要的展宽机制。
