Department of Chemistry, School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan.
J Chem Phys. 2012 Jan 7;136(1):014508. doi: 10.1063/1.3671998.
Rotational dynamics of solvated carbon dioxide (CO(2)) has been studied. The infrared absorption band of the antisymmetric stretch mode in acetonitrile is found to show a non-Lorentzian band shape, suggesting a non-exponential decay of the vibrational and/or rotational correlation functions. A combined method of a molecular dynamics (MD) simulation and a quantum chemical calculation well reproduces the observed band shape. The analysis suggests that the band broadening is almost purely rotational, while the contribution from the vibrational dephasing is negligibly small. The non-exponential rotational correlation decay can be explained by a simple rotor model simulation, which can treat large angle rotations of a relatively small molecule. A polarized Raman study of the symmetric stretch mode in acetonitrile gives a rotational bandwidth consistent with that obtained from the infrared analysis. A sub-picosecond time-resolved infrared absorption anisotropy measurement of the antisymmetric stretch mode in ethanol also gives a decay rate that is consistent with the observed rotational bandwidths.
已研究了溶剂化二氧化碳（CO(2)）的旋转动力学。发现乙腈中反对称伸缩模式的红外吸收带呈现非洛伦兹带形状，表明振动和/或旋转相关函数的指数衰减。分子动力学（MD）模拟和量子化学计算的组合方法很好地再现了观察到的带形状。分析表明，带宽展宽几乎完全是旋转的，而来自振动去相的贡献可以忽略不计。非指数旋转相关衰减可以用简单的转子模型模拟来解释，该模型可以处理相对较小分子的大角度旋转。乙腈中对称伸缩模式的偏振拉曼研究给出了与从红外分析中获得的旋转带宽一致的结果。乙醇中反对称伸缩模式的亚皮秒时间分辨红外吸收各向异性测量也给出了与观察到的旋转带宽一致的衰减速率。
