Knowledge Bank

Self- and air-broadening and shift coefficients for numerous $CH4$ 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 $0.01cm-1$. This data set included both self-broadened $CH4$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH4$ 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 $CH4$ spectra was recorded at higher resolution $(0.0027cm-1)$ 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 $procedurea$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$ lines will be discussed, and air-broadening and shift coefficients for $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH4$ will be compared. We will also compare our measurements with the values on the current HITRAN $compilationb$ and with other available measurements.