SELF- AND AIR-BROADENING AND SHIFT COEFFICIENTS OF $CH_{4}$ LINES IN THE $3 \mu$m REGION

Abstract

Self- and air-broadening and shift coefficients for numerous $CH_{4}$ transitions in the $3 \mu$m region have been determined through analysis of high-resolution absorption spectra recorded by two different Fourier transform spectrometer (FTS) systems. The first set of spectra was recorded using the 1-m FTS at the McMath-Pierce facility of the National Solar Observatory at Kitt Peak; resolution was $0.01 cm^{-1}$. This data set included both self-broadened $CH_{4}$ spectra with cell path lengths of 5,10,25,150, and 2500 cm and pressures ranging from 0.4 Torr to 456 Torr, and air-broadened spectra of $^{12}CH_{4}$ and $^{13}CH_{4}$ with cell path lengths of 5,25,50, and 150 cm and total pressures from about 100 Torr to 400 Torr. A second set of self-broadened $CH_{4}$ spectra was recorded at higher resolution $(0.0027 cm^{-1})$ using the FTS of the Laboratoire de Physique Moleculaire et Applications in Orsay. Path lengths for these spectra varied from 1.7 cm to 4 m, and pressures ranged from less than 1 Torr to over 500 Torr. A multispectrum nonlinear least-squares $procedure^{a}$ was used to fit over 40 spectra simultaneously to determine self- and air-broadening and shift coefficients for more than 500 lines; most of these are in the $\nu_{3}$ and $\nu_{2} + \nu_{4}$ bands. Differences between air- and self-broadening and shifts of $^{12}CH_{4}$ lines will be discussed, and air-broadening and shift coefficients for $^{12}CH_{4}$ and $^{13}CH_{4}$ will be compared. We will also compare our measurements with the values on the current HITRAN $compilation^{b}$ and with other available measurements.