Spectroscopy of methane at 7.6 microns

Self- and air-broadening, pressure-induced shifts, and line mixing have been studied in infrared spectra of methane (CH4) in the 6-9 microns region. The laboratory absorption spectra used in this study were recorded at high resolution (0.006-0.01 cm −1 ) with the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory. Sample temperatures ranged from 210 to 314 K, and broadening gas pressures were between 0.06 and 0.72 atm. The line broadening, shift and mixing parameters (off-diagonal relaxation matrix elements) were obtained by using the multispectrum technique (Benner et al., 1995) to fit selected regions of 20 or more spectra simultaneously. In addition, accurate line center positions and absolute intensities were determined. The temperature dependences of the broadening and shift coefficients were determined for numerous transitions in the ν4 and ν2 bands of 12 CH4. Line mixing was observed in the Q branches and in the J-manifolds of the P and R branches of the ν4 bands of