研究目的
To perform accurate measurements of line strengths and air-broadening coefficients in methane around 1.66 μm using cavity ring down spectroscopy, and compare the results with existing data from HITRAN 2016 database and other experimental studies.
研究成果
Accurate line strengths and air-broadening coefficients for methane lines were measured with uncertainties of 1-5%. The results showed good agreement with HITRAN 2016 database and other experimental studies, suggesting improvements in the accuracy of methane line parameters in spectroscopic databases.
研究不足
The study was limited to methane lines around 1.66 μm and pressures between 10 and 90 mbar. The accuracy of line strength and air-broadening coefficients was affected by the complexity of the methane spectrum and the purity of the gases used.
1：Experimental Design and Method Selection:
Cavity ring down spectroscopy was used to measure absorption spectra of methane mixtures in air at pressures between 10 and 90 mbar at 296 K. Voigt and Galatry profiles were employed for line shape analysis.
2：Sample Selection and Data Sources:
Mixtures of 12CH4/air and 13CH4/air with well-defined mole fractions were prepared. Spectra were recorded for 10 lines of 12CH4 and 2 lines of 13CH
3：List of Experimental Equipment and Materials:
A cavity ring down spectrometer operating around 1.65 μm, a continuous wave external cavity diode laser, an optical isolator, single-mode optical fiber, beam splitter, wavelength meter, acousto-optical modulator, CRD cell with highly reflective mirrors, pressure gauge, and avalanche photodetector were used.
4：65 μm, a continuous wave external cavity diode laser, an optical isolator, single-mode optical fiber, beam splitter, wavelength meter, acousto-optical modulator, CRD cell with highly reflective mirrors, pressure gauge, and avalanche photodetector were used. Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The laser beam was coupled to the CRD cell, and decay times were measured to determine absorption coefficients. Spectra were recorded at different pressures and analyzed using Voigt and Galatry profiles.
5：Data Analysis Methods:
Line strengths and air-broadening coefficients were determined from the linear dependence of line area on the concentration of absorbing molecules, considering uncertainties in line area, pressure, temperature, and mole fraction.
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cavity ring down spectrometer
Used to measure absorption spectra of methane mixtures in air.
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continuous wave external cavity diode laser
Used as a light source for the cavity ring down spectrometer.
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optical isolator
Prevents back reflections into the laser.
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single-mode optical fiber
Used to couple the laser beam to the spectrometer.
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beam splitter
Divides the laser beam for wavelength monitoring and absorption measurements.
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wavelength meter
Monitors the wavelength during spectra recording.
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acousto-optical modulator
Used to quickly and efficiently intermit the beam for measurements of the decay curves.
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CRD cell
A 50-cm long stainless steel cell with two highly reflective mirrors for measuring decay times.
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pressure gauge
Measures pressures up to 100 mbar in the CRD cell.
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avalanche photodetector
Detects light leaking out of the CRD cell for decay time calculations.
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