Experimental air-broadened line parameters in the\bm{ u}\textsubscript band of CH\textsubscriptD

Abstract

In this study, we report the first experimental measurements of air-broadening and air-induced pressure-shift coefficients for approximately 378 transitions in the ν2 fundamental band of CH3D. These results were obtained from analysis of 17 room-temperature laboratory absorption spectra recorded at 0.0056 cm–1 resolution using the McMath–Pierce Fourier transform spectrometer located on Kitt Peak, Ariz. Three absorption cells with path lengths of 10.2, 25, and 150 cm were used to record the spectra. The total sample pressures ranged from 0.129 × 10–2 to 52.855 × 10–2 atm with CH3D volume mixing ratios of approximately 0.0109 in air. The spectra were analyzed using a multispectrum nonlinear least-squares fitting technique. We report measurements for air pressure-broadening coefficients for transitions with quantum numbers as high as J′′ = 20 and K = 15, where K′′ = K′ ≡ K (for a parallel band). The measured air-broadening coefficients range from 0.0205 to 0.0835 cm–1atm–1 at 296 K. All the measured pressure-shift coefficients are negative and are found to vary from about –0.0005 to –0.0080 cm–1 atm–1 at the temperature of the spectra. We have examined the dependence of the measured broadening and shift parameters on the J′′, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = –J′′, J′′, and J′′ + 1 in the QP-, QQ-, and QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%.PACS Nos.: 33.20.Ea, 39.30+w