Laser Raman Spectroscopy (LRS) is a proven and powerful technique in geochemical analyses, especially in the study of
seawater and seafloor hydrothermal minerals anions, such as SO 42-,CO32-,HCO3-, etc. In our lab we have used LD
pumped Nd:YAG Laser operating at 532 nm which is selected for its relatively efficient propagation through seawater to
investigate the LRS of seawater, Na2SO4-NaHCO3 and Na2SO4-Na2CO3 aqueous mixed solutions of different established
concentrations. The sample is interrogated by a 532 nm laser and the Raman backscattering radiation passes through
grating and is recorded on a CCD camera.
In the Raman spectrum of seawater near Qingdao sea area, we find SO42- symmetric stretching band centered at ~981 cm-1 but neither CO32- nor HCO3- signal could be observed . We have detected Raman spectra of mixed solutions and
separated the Raman shift of anions from mixed Raman spectra, fitted the peak area and center with the method of the
multi-peaks Gaussian Fit, then, used the ratios of the fitted areas (the ~981cm-1 band in SO42-, the ~1066cm-1 band in CO32- and ~1016cm-1 band in HCO3-) and established concentrations to estimate the Raman cross-section rations. The results show Gaussian Fit can effectively separate the Raman shifts of anions in mixed solution which close to each other
and conform to the single solution's in the released papers. And we obtain relative Raman cross-sections ratios [SEE MANUSCRIPT FOR EQUATION] are 2.52 and 3.88 respectively at excitation wavelength 532nm.
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