Line mixing and speed dependence in CO2 at 6348 cm-1: Positions, intensities, and air-and self-broadening derived with constrained multispectrum analysis

Abstract Intensity and line shape parameters which predict spectral lines with absolute accuracies better than 0.3% have been determined for transitions of the 30012 ← 00001 band of 16 O 12 C 16 O centered near 6348 cm −1 from 26 high resolution, high signal-to-noise ratio spectra recorded at room temperature with the McMath–Pierce Fourier transform spectrometer. To maximize the accuracies of the retrieved parameters, the multispectrum non-linear least squares retrieval technique was modified to adjust the rovibrational constants ( G , B , D , etc.) and intensity parameters, including Herman–Wallis terms, rather than retrieving the individual positions and intensities. Speed-dependent Voigt line shapes with line mixing were required to remove systematic errors in the fit residuals. Self- and air-broadening (widths and pressure-induced shifts, speed dependence parameters) and line mixing (off-diagonal relaxation matrix elements) coefficients were thus obtained in the multispectrum fit. Remaining errors were minimized by fitting the weak 30011 ← 00001 band of 16 O 13 C 16 O as well as the weak hot bands 31112 ← 01101, 32212 ← 02201, 40012 ← 10001, and 40013 ← 10002 of 16 O 12 C 16 O that contribute interfering absorptions in this spectral window. This study presents the most extensive set of measurements to date for self- and air-broadening and self- and air-shift coefficients of a near infrared band of CO 2 . This is also the first study where line mixing parameters have been experimentally determined for any parallel CO 2 band.

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