Line mixing effects in the ν2+ν3 band of methane

Abstract:

This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixingin air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mix-ing for pure methane in the m2 + m3 band of 12CH4. The speed-dependent Voigt profile with line mixing is used with a multispectrumnonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spec-tra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm1 resolution with the McMath-PierceFourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix ele-ment coefficients of m2 + m3 transitions between 4410 and 4629 cm1 are reported for eighteen pairs with upper state J values between 2and 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 linemixing coefficients for air broadening vary from 0.0005 to 0.0205 cm1 atm1 at 296 K. 2007 Elsevier Inc. All rights reserved.

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