Structural Change of Water with Solutes and Temperature up to 100 °C in Aqueous Solutions as Revealed by Attenuated Total Reflectance Infrared Spectroscopy

Abstract

The attenuated total reflectance infrared (ATR-IR) spectra of several aqueous solutions have been measured by using a newly developed heatable rod-type ATR cell. The OH stretching bands showed systematic change with increasing solute concentrations and these changes can be explained by four different OH components based on curve-fitting results. NaCl solutions show longer H-bond distance character, while carbonate solutions present shorter ones. The Na₂CO₃ 1 M solution conserves this shorter H-bond nature up to 100 °C. On the other hand, the loose nature of NaCl solutions becomes less pronounced at higher temperatures because of the dissociation of pure water clusters. These in situ observations of water structures are generally in agreement with the expected nature of fluids within the earth.