Dynamical structures of intermolecular vibrational motions related with weak hydrogen bonding by terahertz time-domain spectroscopy

利用太赫兹时域光谱和中红外吸收光谱研究了dmso /环己烷溶液的弱氢键。通过在中红外区观察S=O拉伸振动，我们发现DMSO/环己烷溶液中存在DMSO单体和二聚体。我们还通过密度泛函理论的量子计算证明了弱氢键形成的DMSO二聚体的稳定性。与DMSO二聚体形成的浓度范围相对应，我们观察到较宽的太赫兹吸收，表明DMSO二聚体的分子间振动。研究了具有支链结构的饱和烃液体的太赫兹介电响应。我们观察了分支位置和分支结构对太赫兹介电响应的影响。用MD模拟具有环状结构的饱和烃，得到了由欠阻尼振动引起的介电宽响应，与我们的结果相一致。另一方面，我们未能再现介电响应对正构烷烃和支构烷烃的依赖关系。这一结果表明，要理解饱和烃的太赫兹介电响应，必须考虑多体效应。

We investigated weak hydrogen bonding ofDMSO/cyclohexane solution by terahertz time-domain spectroscopy and mid IR absorption spectroscopy. We showed that both of the DMSO monomers and dimers are present in DMSO/cyclohexane solution by the observation of S=O stretching vibrations in the mid-IR region. We also showed the stability of the DMSO dimers formed through weak hydrogen bonding by quantum calculations based on density functional theory. Corresponding to the concentration range of formation of DMSO dimers we observed the broad THz absorption, indicating the intermolecular vibration of the DMSO dimers. We investigated the THz dielectric response of saturated hydrocarbon liquids with branched structures. We observed THz dielectric response dependent on the branching positions and the branched structures. Using MD simulation saturate hydrocarbon with ring-shaped structures shows dielectric broad response originating in underdamped vibrations, corresponding to our results. On the other hand we have failed in reproducing dependence of the dielectric response on the normal alkanes and those with branched structures. This results indicate that considerations of many-body effects are necessary to understand the terahertz dielectric response of saturated hydrocarbon.