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.

Raman spectrum of ethane in methane environment

“…To carry out research, an experimental setup based on the Raman spectrometer described in Petrov and Matrosov [6,12] was used. This instrument was based on a 90°-geometry of scattered light collection and equipped with a continuous wave laser with output power of 2 W at a wavelength of 532 nm.…”

“…In other words, this figure shows the change in the intensities of the ν 3 and ν 1 bands per unit of concentration as a function of concentration. The compressibility factors were calculated using the equation 2 [12] Z P; where R is the molecular gas constant, B(T) and C(T) are the second and third virial coefficients. According to Dymond et al, [15] B(T) = −182.7 cm 3 /mol, C(T) = 10,614 cm 6 /mol 2 for C 2 H 6 at temperature of~300 K. According to the data shown in Figure 3, we can note the following.…”

Quantitative In Situ Monitoring of Parahydrogen Fraction Using Raman Spectroscopy

“…[33][34][35] Therefore, to confirm if sufficient signal could be obtained using our Raman set-up, the spectra from an evacuated NMR tube (≈7 mbar), a tube filled to 4 bar with H 2 gas directly from the hydrogen generator (i.e. nH 2 ), and a tube filled to 4 bar from the pH 2 generator after it had been running for 2 h were compared.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…Petrov and Matrosov reported the pressure dependence of Raman intensities in high‐pressure gases. In the present work, the authors describe a theoretical model for Raman intensity as a function of the pressure of the gas medium considering the compressibility factor, the internal field factor, and the instrumental factor . Proctor et al describe the effect of structural changes on the Raman spectra of methane for pressures up to 165 GPa.…”

“…In the present work, the authors describe a theoretical model for Raman intensity as a function of the pressure of the gas medium considering the compressibility factor, the internal field factor, and the instrumental factor. [210] Proctor et al describe the effect of structural changes on the Raman spectra of methane for pressures up to 165 GPa. The predicted dissociation of CH 4 at ultrahigh pressure to form C 2 H 6 and H 2 is not observed, but an additional discontinuous change in the pressure-induced shift of the Raman peaks is observed at 110 GPa.…”