Knowledge Bank

Air-broadened and $N2$-broadened width coefficients and pressure shifts of transitions in the $\nu 4$ and $\nu 2$ baneds of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$ have been measured from room temperature $0.01cm-1$ resolution absorption spectra recorded at a signal-to-rms noise of -500 with the Fourier transform spectrometer in the McMath telescope of the National Solar Observatory. Total pressures of up to 550 Torr were employed with absorption paths of 5 to 150 cm and a $CH4$ volume mixing ratio of 2.5=% or less. A nonlinear least-squares spectral fitting techinque has been utilized to retrieve the positions, intensities, and the halfwidths of several hundred spectral lines from each of the 22 measured spectra. Unshifted line positions were determined from additional FTS spectra of pure $CH4$ at low pressure, and all spectra were calibrated using well-determined $H2O$ standards near $7\mu m$. The measured positions and widths from the various spectra have been combined to determine the broadening coefficients $(cm-1atm-1)$ and pressure shifts $(cm-1$) and their uncertainties. Lines up to $J\prime \prime =18$ have been analyzed. The experimentally determined halfwidths and pressure shifts will be presented and compared with previously published measurements and calculations.