Analytical Sciences

Abstract − Analytical Sciences, 23(7), 917 (2007).

Detecting a Sodium Chloride Ion Pair in Ice Using Terahertz Time-domain Spectroscopy
Rakchanok RUNGSAWANG, Yuko UENO, and Katsuhiro AJITO
NTT Basic Research Laboratories, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
The hydrogen bond resonance of a sodium chloride (NaCl) ion pair trapped in aqueous ice has been observed by transmission terahertz time-domain spectroscopy. The absorption peak of a sodium chloride ion pair in ice is 1.65 THz at 83 K. By investigating the interaction of the cation and anion with other chemical compounds, we deduce that the absorption peak originates from the hydrogen bond resonance of sodium chloride and water molecules. The charge redistribution that occurs when other ion pairs are added to aqueous salt solution changes the absorption spectrum. Furthermore, the results also indicate that simple molecules such as sodium halides have fingerprints in the terahertz region when the ions are trapped in ice. NaCl ion pairs in seawater and in Ringer's solution were examined.