FT-IR spectra of NaCl–H2O in the region from near to beyond the critical state

Abstract

Water and NaCl–H2O solutions and their molecular spectra at high temperatures and pressures were observed and examined using a new design of hydrothermal diamond anvil cell (HDAC) connected to both a light and an infrared microscope. We have modified the diamond window of the HDAC to have a wide angle to allow the infrared beam to pass the window. Fourier-transform infrared (FT-IR) spectra of NaCl–H2O–D2O were examined at high temperatures and pressures up to 850 °C and 3 GPa. The effect of increasing temperature on water spectra differed from that of increasing pressure. The O–H stretching frequency of water molecules increases with increasing temperature (from 20 to 600 °C), and also with increasing salinity of the solution.