AIR-BROADENING AND SHIFT COEFFICIENTS AND LINE MIXING IN THE $\nu_{3}$ BAND OF $^{12}CH_{3}D$

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Title: AIR-BROADENING AND SHIFT COEFFICIENTS AND LINE MIXING IN THE $\nu_{3}$ BAND OF $^{12}CH_{3}D$
Creators: Devi, V. Malathy; Benner, D. Chris; Smith, M. A. H.; Rinsland, C. P.; Brown, L. R.
Issue Date: 1999
Publisher: Ohio State University
Abstract: A multispectrum nonlinear least squares fitting $technique^{a}$ has been used to determine Lorentz air-broadening coefficients and air-induced shift coefficients for transitions in the $\nu_{3}$ fundamental band of $^{12}CH_{3}D$ in the spectral region between 1154 and $1430 cm^{-1}$. Eleven high-resolution $(0.005 cm^{-1})$ room-temperature absorption spectra, recorded using the 1-m Fourier transform spectrometer (FTS) at the McMath-Pierce facility of the National Solar Observatory at Kitt Peak, were simultaneously analyzed. The data set included both low-pressure (1 to 3 Torr) spectra of 98\% pure $CH_{3}D$ and spectra of lean mixtures ($\sim 1\%)$ of $CH_{3}D$ in dry air at total pressures from about 100 Torr to 400 Torr. Cell path lengths of 25 and 150 cm were used. Air-broadening coefficients were determined for for more than $360 \nu_{3}$ transitions with rotational quantum numbers as high as $J^{\prime \prime} = 17$ and $K^{\prime \prime} = 17$. Air-induced shift coefficients were also determined for most of these transitions. The measured broadening coefficients range from 0.016 to $0.073 cm^{-1} atm^{-1}$ at 296K, and the shift coefficients range vary from about -0.0086 to $+0.0058 cm^{-1} atm^{-1}$. The majority of the shifts are negative, and the positive shifts often involve transitions with $J^{\prime \prime} = K^{\prime \prime}$. The $^{Q}Q$ sub-band $J^{\prime \prime} = K^{\prime \prime}$ transitions are also associated with the smallest broadening coefficients. Weak line mixing effects have been observed in a few high-J transitions with $K^{\prime \prime} = 3$, and we have determined off-diagonal relaxation matrix element coefficients for several $A^{+} A^{-} (A1A2)$ split components. At low to medium values of $J^{\prime \prime}$, the $A^{-} A^{-}$ splittings are very small, and the two components are practically unresolved. Variations of the measured parameters with rotational quantum numbers and differences between the A and E symmetry species will be discussed. We will also compare our measurements with the values on the current HITRAN $compilation^{b}$ and with other available measurements.
Description: $^{a}$ D. Chris Benner, C.P. Rinsland, V. Malathy Devi, M.A.H. Smith. and D. Atkins, JQSRT 53, 705-721 (1995). $^{b}$ L.S. Rothman et al., JQSRT 53, 665-710 (1998).
Author Institution: Department of Physics, The College of William and Mary; Atmospheric Sciences, NASA Langley Research Center; Jet Propulsion Laboratory, California Institute of Technology
URI: http://hdl.handle.net/1811/19570
Other Identifiers: 1999-WH-04
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