Aqueous Dissolved Gas Measurements Using Near-Infrared Raman Spectroscopy

Abstract

Near-infrared Raman spectra of several gases dissolved in an aqueous medium have been acquired and analyzed for the first time. Spectra of dissolved and gaseous CO2, SO2, N2O, dimethyl ether, and O2 are presented and compared. Raman-forbidden bands in the spectrum of gaseous dimethyl ether are observed in the dissolved spectrum; this result can be explained by relaxed selection rules due to lowered symmetry. Raman scattering enhancements in the dissolved phase are measured and shown to compare well with a theoretical prediction accounting for internal field enhancements in water. Dissolved CO2 is measured quantitatively at concentrations from 0 to 250 Torr with the use of the method of partial least-squares, with an average prediction error of 12 Torr.