TEMPERATURE-DEPENDENCE OF LORENTZ AIR-BROADENING AND PRESSURE-SHIFT COEFFICIENTS OF (CH4)-C-12 LINES IN THE 2.3-MU-M SPECTRAL REGION

High-resolution (0.01 cm-1) absorption spectra of lean mixtures of CH4 in dry air were recorded with the McMath-Pierce Fourier transform spectrometer (FTS) of the National Solar Observatory on Kitt Peak at various temperatures between 24 and -61-degrees-C. The spectra have been analysed to determine the values at room temperature of pressure-broadened widths and pressure-induced shifts of more than 740 transitions. The temperature dependence of air-broadened widths and pressure-induced shifts was deduced for approx. 370 transitions in the nu1 + nu4, nu3 + nu4, and nu2 + nu3 bands of (CH4)-C-12 located between 4118 and 4615 cm-1. These results were obtained by analysing a total of 29 spectra simultaneously using a multi-spectral non-linear least-squares fitting technique. This new technique allowed the determination of correlated spectral line parameters (e.g. intensity and broadening coefficient) better than the procedure of averaging values obtained by fitting the spectra individually. This method also provided a direct determination of the uncertainties in the retrieved parameters due to random errors. For each band analysed in this study the dependence of the various spectral line parameters upon the tetrahedral symmetry species and the rotational quantum numbers of the transitions is also presented.