AIR-BROADENING, N2-BROADENING, AND O2-BROADENING AND SHIFT COEFFICIENTS IN THE NU-3 SPECTRAL REGION OF (CH4)-C-12

Pressure-broadening and pressure-induced shift coefficients have been measured for more than 450 transitions in the nu3 region of (CH4)-C-12, between 2650 and 3200 cm-1. The results were obtained by analyzing 29 room-temperature laboratory absorption spectra recorded with 0.01-cm-1 resolution using the McMath Fourier transform spectrometer of the National Solar Observatory (NSO). Absorption cells with path lengths of 5, 25, and 150 cm, sample pressures of 60-550 torr, and CH4 volume mixing ratios of 0.01 or less in dry air, N2 or O2 were used. The broadening and shift coefficients were determined using a nonlinear least-squares spectrum fitting technique. Absorption lines belonging to nu3, nu2 + nu4, 2nu4(2) and 2nu2(2) bands of (CH4)-C-12 were observed in the spectra. Transitions up to J'' = 17 in the nu3, J'' = 12 in the nu2 + nu4, J'' = 9 in the 2nu4(2) and J'' = 4 in the 2nu2(2) bands were included in the analysis. Variations of the measured parameters with tetrahedral symmetry species and rotational quantum numbers of the transitions involved are discussed. Comparisons of the retrieved parameters in various bands in both (CH4)-C-12 and (CH4)-C-13 are performed in order to determine the extent of vibrational dependence.