AIR-, NITROGEN-, AND OXYGEN-BROADENED HALFWIDTH COEFFICIENTS AND PRESSURE-INDUCED LINE SHIFTS IN THE $\nu_{3}$ FUNDAMENTAL OF $^{13}CH_{4}$

Author Institution: Department of Physics, College of William and Mary; Department of Physics, Atmospheric Sciences DivisionAir-broadened, nitrogen-broadened, and oxygen-broadened halfwidths and pressure-induced line shift coefficients have been determined for transitions in the $\nu_{3}$ fundamental band of $^{13}CH_{4}$ by analyzing room-temperature $0.01 cm^{-1}$ resolution absorption spectra recorded in the $2700-3200 cm^{-1}$ spectral region. These data were obtained with the McMath Fourier transform spectrometer of the National Solar Observatory on Kitt Peak. A 99\% ${^{13}}C-enriched$ methane diluted to mixing ratios of 0.003 to 0.01 were used in 5 and 25 cm absorption path cells with total sample pressures ranging between 75 and 500 Torr. The halfwidth and pressure-shift coefficients were retrieved from the data using a non-linear least-squares fitting technique. The unshifted line positions were determined from the spectra of pure ${^{13}}CH_{4}$ at low pressure. The air- to nitrogen-broadened halfwidth ratio was almost one while the air-to-oxygen-broadened halfwidth ratio was found to be -1.06. The derived halfwidth and pressure shift coefficients will be compared to values obtained for identical transitions in the $\nu_{3}$ fundamental of ${{^12}}CH_{4}$ as well as to those in the $\nu_{4}$ fundamental of $^{13}CH_{4}$