Lorentz half-width, pressure-induced shift and speed-dependent coefficients in oxygen-broadened CO 2 bands at 6227 and 6348 cm −1 using a constrained multispectrum analysis

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The McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory (NSO) on Kitt Peak, Arizona, was used to record infrared high resolution absorption spectra of CO 2 spectra broadened by O 2. These spectra were analyzed to measure O 2-broadened half-width coefficients, O 2-induced pressure-shift coefficients and speed dependent parameters for transitions in the 30013←00001 and 30012←00001 bands of 16O 12C 16O located near 6227 and 6348 cm −1, respectively. All spectra were obtained at room temperature using the long path, 6 m base path White cell available at NSO. A multispectrum nonlinear least-squares fitting algorithm employing Voigt line shapes modified to include line mixing and speed dependence was used to fit simultaneously a total of 19 spectra in the 6120–6280 cm −1 (30013←00001) and 6280–6395 cm −1 (30012←00001) spectral regions. 16 of the 19 spectra analyzed in this work were self broadened and three spectra were lean mixtures of CO 2 in O 2. The volume mixing ratios of CO 2 in the three spectra varied between 0.06 and 0.1. Lorentz half-width and pressure-induced shift coefficients were measured for all transitions in the P(50)–R(50) range in both vibrational bands. The results obtained from present analysis have been compared with measurements available in the literature for self-, air-, oxygen- and argon-broadening. No significant differences were observed between the broadening and shift coefficients of the two bands. The N 2-broadened half-width and pressure-shift coefficients were computed from measured air- and O 2-broadened width and shift coefficients.