Pressure dependence of the Raman signal intensity in high‐pressure gases

Abstract

At present gas analysis based on Raman, spectroscopy is actively developed. In most cases, to achieve the required Raman signal intensity, compression of the gas medium is used. However, in comparison with normal conditions, the character of motion of molecules and their electric properties change in high‐pressure gas media, thereby violating a linear dependence of the Raman signal intensity on the concentration of molecules and the gas pressure. In the present work, a theoretical model is presented that describes the Raman signal intensity as a function of the pressure of the gas medium considering the compressibility factor, the internal field factor, and the instrumental factor. To verify the model, changes in the Raman signal intensities of vibrational bands of nitrogen and oxygen in the pressure range 1–80 atm and carbon dioxide in the pressure range 1–60 atm are investigated. Under these conditions, we observe a deviation of ~3% from a linear dependence for nitrogen, ~7% for oxygen and ~80% for carbon dioxide, which is in good agreement with the theoretical model. Raman shifts, half‐widths of Q‐branches of vibrational bands ν1 (and 2ν2 for carbon dioxide) of these molecules and also ratio of integral intensities I(2ν2)/I(ν1) for carbon dioxide under these conditions are investigated. Copyright © 2016 John Wiley & Sons, Ltd.