Knowledge Bank

Room-temperature air-broadened Lorentz halfwidths for more than 150 transitions (for $J\le 15$) in the $\nu 4$ fundamental of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH4$ between 1200 and $1380cm-1$ have been determined by analyzing $0.01-Cm-1-1$ resolution spectra recorded with the Fourier transform spectrometer in the McMath telescope of the National Solar Observatory on Kitt Peak. A 99% $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$-enriched $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH4$ sample diluted to *** 0.5% by mixing the sample with approximately 200, 350 and 505 Torr of dry air was used in a 50-cm long absorption cell. The halfwidths were determined using nonlinear least-squares spectral curve fitting. The measured air-broadened halfwidths are compared with values determined previously for several transitions in the same band using a tunable diode laser spectrometer $system.1$ Comparisons with identical transitions in the $\nu 4$ band of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$ will also be made.