The work deals with the effects that lead to changes in Raman intensities of nitrogen and oxygen as their pressure increases. It was found that when these gases are compressed up to 80 atm, the intensities of their rovibrational Raman bands per molecule increased by approximately 3%. A theoretical model is proposed for describing Raman intensities in high-pressure gaseous media.
Spectroscopic methods for pressure determination of methane-containing gaseous medium are discussed. The results of investigation of changes in the relative peak intensities of the main methane Raman bands in the pressure range 1-55 bar are presented. New methods for the non-contact pressure determination of methane-containing gaseous media are proposed.
The present work focuses on the influence of CH<sub>4</sub> environment on the changes in Raman spectra of n-C<sub>5</sub>H<sub>12</sub> and i-C<sub>5</sub>H<sub>12</sub> in the gaseous phase. It was found that in binary gas mixtures with an overwhelming content of CH<sub>4</sub>, the majority of the n-C<sub>5</sub>H<sub>12</sub> and i-C<sub>5</sub>H<sub>12</sub> Raman bands shifted toward lower wavenumbers. Moreover, there is also a redistribution of intensities between certain Raman bands of n-C<sub>5</sub>H<sub>12</sub> and i-C<sub>5</sub>H<sub>12</sub>. The obtained results will be essential for Raman diagnostics of natural gas composition.
The study is dedicated to the problems of wavenumber calibration of multichannel Raman spectrometers. We present a calibration method based on the combined use of the neon emission spectrum and pure rotational lines of the hydrogen Raman spectrum.
In the present work, the method of evaluation of component composition of natural gas is based on the decomposition of Raman spectrum into spectra of the individual components is described. To implementing of this method the spectral ranges 250-2500 cm<sup>-1</sup> and 3600-3700 cm<sup>-1</sup> were selected. The Raman spectra of the main components of natural gas are presented. Results of Raman gas analyzer approbation on a real natural gas sample are presented. A comparison of the experimental results obtained with the results of chromatographic analysis demonstrates their good agreement. It is experimentally established that the given Raman gas analyzer can reliably determine the content of all molecular natural gas components whose content exceeds 0.005% for 100 s.
A possibility of applying SERS effect to enhance the intensity of the Raman spectra of gaseous media is investigated. More than 6-fold increase in Raman signals of the main components of air has been experimentally recorded due to increasing the electromagnetic field near an aluminum holographic diffraction grating. The average gain of Raman signals in the 30-nm layer at the grating – gaseous medium boundary was ~ 3×10<sup>3</sup>.
Nowadays the sources of long-wavelength optical radiation (far infrared, terahertz range) are developed intensively. They have good perspectives in different fields of biology, medicine, security systems etc. This implies the need to have the detectors of radiation with advanced parameters <sup>1,2</sup>. Golay cell <sup>3</sup> is one of the most sensitive detector types available at the time being despite, the strong development of semiconductor detectors <sup>4 – 6</sup>. In Golay cell the energy is measured by the expansion of the gas in the sealed chamber: the gas absorbs the energy and presses the flexible membrane, thus the change of volume is registered. The disadvantages of these detectors are relatively high price, big size and vibration susceptibility. In our paper we consider the method of radiation detecting that is similar to one that is used in Golay cell but based on gas temperature measurement.
It is shown that the main problem, arising when designing a stationary Raman gas analyzer intended to monitor gaseous air pollutions, is to get SRS signals of sufficient intensity. The engineering solutions are presented that provide the required sensitivity (~ 50–100 ppb). It is achieved by compressing a gas medium under analysis and gaining intensity of the exciting laser radiation.
A prototype of a stationary Raman gas analyzer with the improved sensitivity is described. The improvement is provided by using both a device for compressing analyzed gas media and a specialized effective spectral device as a part of the gas analyzer. The experimental testing of the modified Raman gas analyzer was performed in the probing of atmospheric air that confirmed the extreme sensitivity of the prototype was equal to ~ 1 ppm.