Measurements of air broadened width and air induced shift coefficients and line mixing in the ν5 band of 12CH3D

Abstract In this study we report the first experimental measurements of air-broadening and air-induced pressure-shift coefficients for approximately 400 transitions in the ν5(E) perpendicular band of 12CH3D in the spectral region 1276– 1600 cm −1 . These results were obtained from analysis of 11 room temperature laboratory absorption spectra recorded at 0.005 cm −1 resolution with the McMath–Pierce Fourier transform spectrometer located on Kitt Peak National Solar Observatory. A multispectrum non-linear least-squares fitting algorithm was used in retrieving the results. The measured broadening coefficients vary from to 0.0265 to 0.0735 cm −1 atm −1 at 296 K for transitions up to J″=17 and K″=12, including 12 forbidden lines with Δ K=±2 (5 O Q and 7 S Q) . The corresponding pressure-induced shift coefficients range from +0.0003 and −0.0088 cm −1 atm −1 and the majority of these are negative. Subsets of air-broadened width coefficients vary somewhat smoothly as a function of the rotational quanta, and this behavior has been modeled to ±5% using empirical expressions. The off-diagonal relaxation matrix coefficients, Wij, in cm −1 atm −1 at 296 K which are associated with line mixing were determined for a few transitions with K″=3 ( A + A − splitting) in the PP and PQ sub-bands. The broadening and pressure-shift coefficients obtained from the analysis are compared with values previously determined by us for similar transitions in the ν6(E) perpendicular band of 12CH3D and with other values reported in the literature.