HIGH RESOLUTION INFRARED SPECTRA AND VIB-ROTATIONAL ANALYSIS OF THE $\nu_{3}$ AND $\nu_{4}$ REGIONS OF CHLORINE NITRATE IN THE TEMPERATURE RANGE 190 TO 297 K

$^{a}$C. P. Rinsland et al., J. Geophys. Res. D 90, 7931 (1985). $^{b}$A. Goldman, C. P. Rinsland, J.-M. Flaud, and J. Orphal, J. Quant. Spectrosc. Rad. Transf. 60, 875 (1998). $^{c}$W. Bell, G. Duxbury, and D. D. Stuart, J. Mol. Spectrosc. 152, 283 (1992). $^{d}$S. Xu, T. A. Blake, and S. W. Sharpe, J. Mol. Spectrosc. 183, 228 (1996). $^{e}$H. S. P. M\""uller, P. Helminger, and S. H. Young, J. Mol. Spectrosc. 181, 363 (1997).Author Institution: CNRS, Laboratoire de Photophysique Mol\'{e}culaire; Optical Technology Division, NIST Gaithersburg; Optical Technology Division, Institute for OptoelectronicsChlorine nitrate plays an important role in upper atmospheric chemistry. It was first detected in the stratosphere by Rinsland $et al.^{a}$ by observation of the $\nu_{4}$ band a-type Q-branch. There have been a number of laboratory infrared spectroscopic studies on the $\nu_{4}$ band since that $ime.^{b}$ Among them is the work of Bell, $Duxbury and Stuart^{c}$ who used a tunable diode laser to study and model the a-type Q-branches of the two chlorine isotopic species $^{35}Cl$ and $^{37}Cl$ as well as that of the $\nu_{4} + \nu_{9} - \nu_{9}$ hot band. At room temperature, even at the high resolution of a diode laser, the bands are only partially resolved due to the overlapping of lines of the two main isotopic species and of lines from several strong hot bands. A beautifully resolved spectrum of the $\nu_{4}$ region over a limited range of J and $K_{a}$ was obtained later by $Xu, Blake and Sharpe^{d}$ from diode laser spectra of a molecular jet at about 7 K. In this work, 29 spectra of the region 750 to $900 cm^{-1}$ at temperatures ranging from 190 to 297 K and air pressures ranging from zero to 156 hPa were recorded at DLR with resolutions of 0.00094 to $0.0083 cm^{-1}$. Using the ground-state constants of $M\""{u}ller et al.^{e}$ a vib-rotational analysis of the $\nu_{4}$ and $\nu_{3}$ fundamental bands as well the hot band, $\nu_{4} + \nu_{9} - \nu_{9}$, of the most abundant $^{35}Cl$ isotopomer was carried out using the spectrum recorded at 191 K with the highest resolution and a zero air pressure. The corresponding cold bands for the lesser abundant isotope were partially assigned. Upper state rotational Hamiltonian constants were determined allowing precise modeling of the contours of the $\nu_{4}$ fundamental Q-branches over the temperature and pressure ranges studied as shown by comparisons with the other spectra