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

At present gas analysis based on Raman, spectroscopy is actively developed. Inmost 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 ofmolecules and the gas pressure. In the present work, a theoreticalmodel 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 themodel, changes in the Raman signal intensities of vibrational bands of nitrogen and oxygen in the pressure range 1-80 atmand carbon dioxide in the pressure range 1-60 atmare investigated. Under these conditions, we observe a deviation of similar to 3% from a linear dependence for nitrogen, similar to 7% for oxygen and similar to 80% for carbon dioxide, which is in good agreement with the theoretical model. Raman shifts, half-widths of Q-branches of vibrational bands.v(1) (and 2v(2) for carbon dioxide) of these molecules and also ratio of integral intensities I(2v(2))/I(v(1)) for carbon dioxide under these conditions are investigated. Copyright (c) 2016 John Wiley & Sons, Ltd.