THz-TDS Study on Tetrabutylammonium Bromide Hydrate

Tetrabutylammonium bromide (TBAB) hydrate, a semi-clathrate hydrate was investigated by terahertz time-domain spectroscopy (THz-TDS) in the region from 0.1 to 1.5 THz. The high absorption was observed in the whole region in comparison with that in ice and propane hydrate. In addition, absorption band was clearly observed around 1.1 THz, though ice and propane hydrate does not have such a peak at this frequency. This peak in TBAB hydrate may be caused by intermolecular vibration of tetrabutylammonium ion because TBAB crystal also has infrared activity at 1.4 THz. In TBAB hydrate, tetrabutylammonium ion is isolated by hydrogen-bonded water molecules, which might cause the absorption peak shift to lower frequency. THz- TDS is worthwhile to observe the interaction of guest-guest and/or guest-host molecules.