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A brief review of the Raman spectroscopic studies of methane gas hydrates is given, supported by some new measurements done in our laboratory.

Raman spectra of a pure CH4 sample, two CH4C2 H6 mixtures and a CH4N2 mixture were obtained as a function of pressure at pressures up to 39.6 MPaA (MPa absolute). These spectra are presented in the region 3120–2980 cm−1. A clear pressure dependence of the area ratio between two weak methane bands, ν3 (asymmetric CH stretching) and 2ν2 (overtone of the asymmetric CH bending), is observed; the methane ν3 band intensity is lowered relative to the methane 2ν2 as the pressure is raised. The intensity ratios between these two bands, I(ν3)/I(2ν2), were determined and plotted as a function of pressure. Surprisingly it is observed that the ratio at a fixed pressure is independent of the composition and thereby of the surroundings in which the methane molecule is vibrating. A model function to predict the pressure is given. From a practical point of view, the present results could be useful for determining directly the total pressure in methane mixtures the composition of which is not known. Copyright © 2002 John Wiley & Sons, Ltd.

Raman spectra of methane and methane–ethane mixtures (100, 85, and 49 mole % CH4) have been obtained as a function of pressure in the pressure range 0.1 to 15.3 MPaA (MPa absolute). For these mixtures methane v1 (symmetric C–H stretching) band positions are given as a function of pressure; for pure methane they are in agreement with previous results. The new data on the methane v1 band position of ethane-containing mixtures clearly depend on the kind of molecules surrounding the vibrating methane molecule. The v1 band position decreases with increasing pressure; the stronger the dependency, the higher the content of ethane. The ethane v1 band position in the two mixtures showed the same kind of dependency. A qualitative explanation for this behavior is attempted, relating it to changes in van der Waals-type interactions on pressure.

A system for obtaining Raman spectra of gases at high pressure has been constructed. In order to ensure that a natural gas sample is totally representative, a high-pressure gas-measuring cell has been developed, built up by stainless steel fittings and a sapphire tube. The design and construction of this cell are described. A perfect pressure seal has been demonstrated up to 15.0 MPaA(MPa absolute). The cell has been successfully used to obtain Raman spectra of natural gas samples. Some of these spectra are presented and assigned. The most remarkable observation in the spectra is that it is possible to detect hydrogen sulfide at concentrations of 1–3 mg H2S/Nm3. An attempt to make a quantitative analysis of natural gas by the so-called “ratio method” is presented. In addition to this, the relative normalized differential Raman scattering cross sections for ethane and i-butane molecules at 8.0 MPaAand 10.2 MPaAhave been determined.

Low frequency Raman spectra of some nylon samples are presented. In order to ensure the reliability of near-IR (NIR) FT-Raman spectra at low frequencies, spectra obtained by excitation with a Nd—YAG laser are compared with spectra recorded with excitation in the visible region. Spurious laser emission lines appear due to the insufficiency of the spike filter at low frequencies. Samples of nylon 6, nylon 6.6 and nylon 12 are investigated. The NIR FT-Raman spectra are reliable down to approximately 50 cm−1, when corrections for spurious laser lines and spectrometer response are performed in a proper way. In order to avoid the influence of the intense Rayleigh line the spectra are also presented in the R( ν ) representation. A band around 100 cm−1 is assigned to a hydrogen bond mode. This band might depend upon the nylon structure.

Des spectres Raman de polyamides (nylons) ont ete realises par excitation a 1064 nm. Des spectres basses frequences ont ete obtenus aux alentours de 50 cm -1 . Une bande proche de 100 cm -1 a ete assignee a un mode correspondant. a des liaisons hydrogene. Des etudes quantitatives des bandes basses frequences ont ete realisees en utilisant les vibrations de «bending» du groupe methylene proche de 1450 cm -1 comme etalons internes. La bande proche de 100 cm -1 pourrait donner des informations sur la liaison hydrogene (c-a-d:structure secondaire) des polyamides

Improvement of a conventional JEOL Raman spectrometer with a single channel photo multiplier detector is described. New optical components [fibers, mirror, lens, and charge coupled device detector (CCD)] have been chosen to design a high quality and easy‐to‐use instrument. Tests have shown that with this modified spectrometer, Raman spectra can be acquired of a quality comparable to the spectra obtained previously, but the time needed to obtain a spectrum is markedly reduced. Selected test spectra and a simple calibration procedure to obtain the wavenumber values from the band CCD pixel position are presented.