Line mixing effects in the ν2 + ν3 band of methane |
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Authors: | Adriana Predoi-Cross Anildev V Unni V Malathy Devi Linda R Brown |
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Institution: | a University of Lethbridge, Department of Physics, 4401 University Drive, Lethbridge, AB, Canada T1K 3M4 b The College of William and Mary, Department of Physics, Williamsburg, VA, USA c Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA |
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Abstract: | This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing in air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mixing for pure methane in the ν2 + ν3 band of 12CH4. The speed-dependent Voigt profile with line mixing is used with a multispectrum nonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spectra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm−1 resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix element coefficients of ν2 + ν3 transitions between 4410 and 4629 cm−1 are reported for eighteen pairs with upper state J values between 2 and 11. The observed line mixing coefficients for self broadening vary from 0.0019 to 0.0390 cm−1 atm−1 at 296 K. The measured line mixing coefficients for air broadening vary from 0.0005 to 0.0205 cm−1 atm−1 at 296 K. |
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Keywords: | Methane Line mixing Off-diagonal relaxation matrix element Widths Pressure shifts Speed-dependent Voigt Multispectrum retrievals |
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