BROADENING AND SHIFT COEFFICIENTS IN THE $3-{\mu}m$ BANDS OF HCN
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Date
2002
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Publisher
Ohio State University
Abstract
While there have been a number of recent studies of room-temperature $N_{2}$-broadening of spectral lines in various molecular bands of HCN, the corresponding pressure-induced line shifts have not been measured. Only three limited studies of the temperature-dependence of $N_{2}$-broadening in HCN have been reported, and air- and $O_{2}$-broadening have been examined only at room temperature for single $HC^{15}N$ rotational $line.^{a}$ We have recorded over 80 new infrared spectra of HCN broadened by $N_{2}, O_{2}$, or air at room temperature and low temperatures using a 50-cm coolable cell with the McMath-Pierce Fourier transform spectrometer (FTS) of the National Solar Observatory on Kitt Peak, Arizona. Most of these spectra cover bandpasses of either $2750-3950 cm^{-1}$ at $0.008 cm^{-1}$ resolution or $600-3000 cm^{-1}$ at $0.005 cm^{-1}$ resolution. Volume mixing ratios of HCN in the broadening gases were 0.1% or less, and total sample pressures ranged from 12 Torr to over 500 Torr. Most spectra were recorded at temperatures from room temperature down to near the freezing point of HCN $(-13^{\circ}C)$, and some spectra were successfully recorded at temperatures down to about $-60^{\circ}C$. Several spectra of low pressures (about 0.1 Torr) of purified HCN were also recorded to provide line positions unaffected by pressure-induced shifts. An initial group of 19 of these absorption spectra have been analyzed simultaneously using our multispectrum nonlinear least-squares $technique^{b}$ to determine $N_{2}$-broadening and shift coefficients and their temperature dependences for transitions up to $J^{\prime\prime} = 30$ in the $\nu_{1}$ fundamental band of $H^{12}C^{14}N$. The results for $N_{2}$-broadening compare well with available values reported in the literature. In particular, the $N_{2}$-broadening temperature-dependence exponent n shows a quantum-number dependence similar to that observed in the $\nu_{2}$ band by Schmidt $et al.^{c}$ Analysis of air-broadening and shifts in the $\nu_{1}$ band is in progress, as well as work on the $\nu_{2}$ and $2\nu_{2}$ band systems.
Description
$^{a}$J.-M. Colmont, J. Mol. Spectrosc. 114, 298-304 (1985). $^{b}$D. Chris Benner, C. P. Rinsland, V. Malathy Devi, M. A. H. Smith and D. Atkins, JQSRT 53, 705-721 (1995). $^{c}$C. Schmidt, J.-C. Populaire, J. Walrand, G. Blanquet and J.-P. Bouanich, J. Mol. Spectrosc. 158, 423-432 (1993).
Author Institution: Atmospheric Sciences, NASA Langley Research Center; Department of Physics, The College of William and Mary; Department of Physics, National Solar Observatory
Author Institution: Atmospheric Sciences, NASA Langley Research Center; Department of Physics, The College of William and Mary; Department of Physics, National Solar Observatory