Citation:
Abstract:
Room temperature Lorentz air-broadened halfwidth and pressure-induced air-shift coefficients were measured for 1011 transitions inthe octad region of methane between 4100 and 4635 cm1. These measurements were made by analyzing 10 laboratory absorption spec-tra recorded at 0.011 cm1 resolution using the McMath–Pierce Fourier transform spectrometer located at the National Solar Observa-tory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 2.05 and 150 cm. The total samplepressures ranged from 99 to 400 torr with CH4 volume mixing ratios of 0.01 in dry air. The spectral line parameters were retrieved using amultispectrum nonlinear least squares technique. Transitions belonging to five bands of the octad polyad were observed, namely m2 +2m4,m1 + m4, m3 + m4,2m2 + m4, and m2 + m3. The numbers of measurements by bands are: 33 for m2 +2m4, 180 for m1 + m4, 635 for m3 + m4, 33 for2m2 + m4, and 130 for m2 + m3. Transitions with rotational quantum number J up to 16 are included in the analysis. The measured widthand shift coefficients vary according to the tetrahedral symmetry species and the rotational quantum numbers of the transitions. Theretrieved parameters from this study are compared with prior results, in part to estimate absolute accuracy and determine the extentof vibrational dependence of widths and shifts. 2006 Elsevier Inc. All rights reserved.
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