Aqueous Dissolved Gas Measurements Using Near-Infrared Raman Spectroscopy

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 CO 2 , SO 2 , N 2 O, dimethyl ether, and O 2 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 CO 2 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.