Air- and self-broadened half widths, pressure-induced shifts, and line mixing in the ν2 band of 12CH4

Abstract:

Lorentz self- and air-broadened half width and pressure-induced shift coefficients andtheir dependences on temperature have been measured from laboratory absorptionspectra for nearly 130 transitions in the ν2 band of 12CH4. In addition line mixingcoefficients (using the relaxation matrix element formalism) for both self- and air-broadening were experimentally determined for the first time for a small number oftransitions in this band. Accurate line positions and absolute line intensities were alsodetermined. These parameters were obtained by analyzing high-resolution (0.003 to0.01 cm1) laboratory spectra of high-purity natural CH4 and air-broadened CH4 recordedat temperatures between 226 and 297 K using the McMath–Pierce Fourier transformspectrometer (FTS) located at the National Solar Observatory on Kitt Peak, Arizona.A multispectrum nonlinear least squares technique was used to fit short (5–15 cm1)spectral intervals in 24–29 spectra simultaneously. Parameters were determined for ν2transitions up to J″¼16. The variations of the measured broadening and shift parameterswith the rotational quantum number index and tetrahedral symmetry species areexamined. The present results are also compared with previous measurements availablein the literature.Published by Elsevier Ltd.

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