In the range of 2500–3500 cm –1 of methane Raman spectrum there are two bands (2ν4 and 2ν2) which are under Fermi resonance with an intense ν1 band. It was found that when the pressure changes from 1 to 55 atm, the peak intensity of the 2ν4 band increases by ~ 9% and peak intensity of the 2ν2 band increases by ~ 6.5% relative to the ν1 intensity. An analysis of the integrated intensities showed that in this pressure range the ratio 2ν4/ν1 increases by ~ 7%, the ratio 2ν2/ν1 (taking into account the additional contribution of the lines of the ν3 band) increases by ~ 0.7%.
This work is aimed to study of the ν1 band of the methane Raman spectrum in the pressure range of 1–80 atm. The wavenumber calibration was performed using the rotational–vibrational structure of the ν3 methane band. It was established, that pressure shift coefficient is about –0.02 cm–1 /atm, pressure broadening coefficient is about 0.005 cm– 1 /atm. According to the obtained experimental data, in the region of 2914–2916 cm–1 , with an increase in pressure, either the van der Waals methane complexes begin to make a noticeable contribution to the intensity of the ν1 band, or collision–induced Raman scattering increases in this range.
The results of the retrievals of methane total column in the atmosphere of Western Siberia using high resolution IR solar spectra registered in May and June 2019 by the Bruker IFS125M Fourier spectrometer are presented. The obtained time series of methane total column are analyzed and compared with the collocated IASI satellite data.
Surface-enhanced Raman spectroscopy is a promising method for analysis of gas media composition. In this work we present an analysis of resonant metal-dielectric holographic gratings providing an essential local field enhancement due to excitation of the surface plasmon-polaritons. It is shown that structure parameters yielding an optimum far-field resonance excitation are not necessarily correspond to optimum local field maximum.
This paper presents a technique for simulation the nitrogen Raman vibrational-rotational band, which is one of the main gaseous components of combustion products. The deviation of the temperature values obtained by fitting the spectra from the reference data was less than 3 K in the range of 300-600 K. It is shown that neglecting of the effects of vibrational-rotational interaction leads to an increase in the measured temperature by 3 K.
The description of the developed automatic weather station for the Arctic region is presented. The station provides information to the remote user measured data such as three-component vector of wind velocity, air temperature and humidity, atmospheric pressure, precipitation parameters, solar radiation intensity, snow cover depth, and soil temperature profile (including ground surface temperature). The solution to this problem is possible only through the use of automated systems that can data acquisition, process and transmit meteorological information to a remote user in an automatic mode without human intervention.
The main components of the synthesis gas are hydrogen, carbon monoxide, methane and carbon dioxide. In this work, we studied the spectral characteristics of the most intensive Raman bands of these components as a function of environment at a fixed pressure of 25 bar. It has been established that, under these conditions, the change in the characteristics of pure rotational hydrogen lines is negligible, and the vibrational bands of methane, carbon monoxide and carbon dioxide shift to a few tenths of cm–1. The data obtained allow to improve the accuracy of determining the composition of the synthesis gas using Raman spectroscopy.
The effect of methane environment and increased pressure (up to 25 bar) on the stability of the conformational equilibrium of gaseous n-butane was investigated using Raman spectroscopy. It is established that under these conditions the change in the concentration of trans and gauche-conformers of n-butane is less than 1%. The results obtained will be useful for Raman diagnostics of natural gas composition.
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 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.
The present work focuses on the influence of CH4 environment on the changes in Raman spectra of n-C5H12 and i-C5H12 in the gaseous phase. It was found that in binary gas mixtures with an overwhelming content of CH4, the majority of the n-C5H12 and i-C5H12 Raman bands shifted toward lower wavenumbers. Moreover, there is also a redistribution of intensities between certain Raman bands of n-C5H12 and i-C5H12. The obtained results will be essential for Raman diagnostics of natural gas composition.
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 1,2. Golay cell 3 is one of the most sensitive detector types available at the time being despite, the strong development of semiconductor detectors 4 – 6. 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.
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-1 and 3600-3700 cm-1 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 ~ 3×103.
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.