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

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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.