15min:
BROADENING AND SHIFT COEFFICIENTS IN THE 3-µm BANDS OF HCN.

M. A. H. SMITH, C. P. RINSLAND, Atmospheric Sciences, NASA Langley Research Center, Mail Stop 401A, Hampton, VA 23681-2199; V. MALATHY DEVI, D. CHRIS BENNER, Department of Physics, The College of William and Mary, Box 8795, Williamsburg, VA 23187-8795; AND M. DULICK, National Solar Observatory, P. O. Box 26732, Tucson, AZ 85726-6732.

While there have been a number of recent studies of room-temperature N2-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 N2-broadening in HCN have been reported, and air- and O2-broadening have been examined only at room temperature for single HC15N rotational line. We have recorded over 80 new infrared spectra of HCN broadened by N2, O2, 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\circC), and some spectra were successfully recorded at temperatures down to about -60\circC. 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 to determine N2-broadening and shift coefficients and their temperature dependences for transitions up to J''=30 in the nu1 fundamental band of H12C14N. The results for N2-broadening compare well with available values reported in the literature. In particular, the N2-broadening temperature-dependence exponent n shows a quantum-number dependence similar to that observed in the nu2 band by Schmidt et al. Analysis of air-broadening and shifts in the nu1 band is in progress, as well as work on the nu2 and 2 nu2 band systems.