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In this work, we measured the intensities of Q-branches of the ν 1 , ν 2 and ν 3 bands in the polarized and depolarized methane Raman spectra in the pressure range of 1-60 atm. It was established that the pressure dependence of depolarization ratios of the ν 2 and ν 3 bands are negligible. In turn, the depolarization ratio of the ν 1 band increases with increasing pressure and reaches approximately 0.0045 at 60 atm. These data are more precise than previously published ones because ν 1 band intensities were determined taking into account the contribution of overlapping lines of ν 3 band. The presented data will be useful in calculating the methane polarizabilities at high pressure, as well as in calculating methane Raman spectra for measuring the natural gas composition using Raman spectroscopy.

Changes in the spectral characteristics of the vibrational bands of n-butane have been studied in the spectral range 300–1100 cm–1 at a temperature varied from 285 to 365 K and a methane pressure varied in the range 2–40 atm. It was established that the enthalpy of the trans–gauche transition of n-butane in the gas phase is 657 ± 66 cal/mol. The methane pressure in the given range was found to have a negligible effect on the conformational equilibrium of n-butane. The impact of changes in the spectral characteristics of n‑butane on the accuracy of measuring the composition of natural gas using Raman spectroscopy was determined. [ABSTRACT FROM AUTHOR]

The peak positions and halfwidths of the Q-branch of the ν1 band and the ratios of intensities of the Q-branches of ν3 and 2ν2 bands of methane are measured in a methane–helium mixture at different pressures and concentrations. An empirical model is developed for estimation of the He concentration in a methane-containing medium from measurements of the above parameters. The error in the He concentration is found to be less than 1% when using the ν1 band halfwidth. The paths of improvement of this technique and enhancement of its accuracy are considered. [ABSTRACT FROM AUTHOR]

We have studied the particular features of the Raman spectra of gaseous n-butane, isobutane, n-pentane, and isopentane in a methane medium at a pressure of 25 atm. It has been found that, under these conditions, changes in the conformational equilibria of these molecules are negligible, and most significant changes in the spectra are observed in the range of 2850-3000 cm-1, in which bands corresponding to the stretching vibrations of CH2 and CH3 groups shift to lower frequencies. The data obtained will be usefull in determining the composition of natural gas using Raman spectroscopy. [ABSTRACT FROM AUTHOR]

We have developed a spectrometer designed to record spontaneous Raman scattering (SRS) spectra in gaseous media. The spectrometer has improved sensitivity due to using a high-performance spectral instrument and also a device for compressing the analyte gaseous medium. We present the results of an experimental test of the spectrometer, and show that its limiting sensitivity for methane is <1 ppm. [ABSTRACT FROM AUTHOR]