Knowledge Bank

We have recorded a series of high-resolution absorption spectra of methane broadened by dry air and by $N2$ at temperatures from $-630C$ to $20C$ using the McMath Fourier transform spectrometer at the National Solar Observatory on Kitt Peak. The spectra cover a wavenumber range from approximately 500 $cm-1$ to 1500 $cm-1$ at a resolution of $0.01cm-1$. These spectra have been analyzed to determine pressure broadening and line shift coefficients at low temperatures for over 150 lines in the $\nu 4$ fundamental band of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$. These values, along with previous FTS measurements at room $temperature1$, have been used to determine the temperature dependence of the air- and $N2$-broadening and shift coefficients for these $CH4$ lines. Recent TDL measurements of low-temperature $N2$-broadening for a small group of $lines2$ are in excellent agreement with our results. Since the present results cover a wide range of rotational quantum numbers (J"" up to 13), the variation of the halfwidths and shift from line to line within the $\nu 4$ band will be examined.