Ion effects on solution structure monitored by terahertz time-domain spectroscopy

Kondo, Masato; Oshima, Yasuhiro*; Tsubouchi, Masaaki

We investigated the dielectric relaxation of aqueous ionic solutions by applying the terahertz time-domain spectroscopy (THz-TDS) to obtain the global picture of ionic hydration. We measured the dielectric spectra in the 0.2-1.8 THz region, and found the significant effects of dissolved cations on the imaginary part of the spectra. Especially in the high frequency region, the dielectric spectra increased in intensity as compared to that of pure water, which cannot be explained by the hydration effect within first hydration shells. This result indicates the dielectric relaxation was enhanced in the ionic solution, implying the dissolved ions weaken the hydrogen bonding of water beyond ion hydration shells.