HIGH-RESOLUTION ANALYSIS OF THE 83.3 μm TORSIONAL BANDS OF THE ClONO2 MOLECULE

Abstract

Chlorine nitrate (\chem{ClONO_2}) is a very important atmospheric "reservoir" of ClO and \chem{NO_2}, destroying stratospheric ozone through catalytic cycles\footnote{P. J. Crutzen, \textit{Quart. J. Royal Met. Soc.} \textbf{96}, 320 (1970); M. J. Molina and F. S. Rowland, \textit{Nature} \textbf{249}, 810 (1974).}. It was detected for the first time by infrared (IR) spectroscopy\footnote{D. G. Murcray \textit{et al.}, \textit{Geophys. Res. Lett.} \textbf{6}, 857 (1979).}, a detection confirmed and extended by the MIPAS\footnote{H. Fischer \textit{et al.}, \textit{Atmos. Chem. Phys.} \textbf{8}, 2151 (2008).} and the ATMOS satellite experiments\footnote{R. Zander \textit{et al.}, \textit{Geophys. Res. Lett.} \textbf{13}, 757 (1986).}. Many high-resolution microwave and mid-IR spectroscopy studies of \chem{ClONO_2} have been published\footnote{J. Orphal, M. Birk, G. Wagner, and J.-M. Flaud, \textit{Chem. Phys. Lett.} \textbf{690}, 82 (2017).}. However, \chem{ClONO_2} presents 4 fundamentals in the far-IR region below 600 \wn, with the lowest one corresponding to the torsional mode \nub{9} around 83.3 $\mu$m. This band has been observed at low resolution\footnote{J. W. Fleming, \textit{Infrared Phys.} \textbf{18}, 791 (1978); K. V. Chance and W. A. Traub, \textit{J. Mol. Spectrosc.} \textbf{95}, 306 (1982).} but without precise determination of the band center. More recently, the analysis of the mid-IR \nub{8} and \nub{8} + \nub{9} band spectral regions of $^{35}$\chem{ClONO_2} allowed the indirect but accurate determination of the \nub{9} band center\footnote{J.-M. Flaud, W. J. Lafferty, J. Orphal, M. Birk, and G. Wagner, \textit{Mol. Phys.} \textbf{101}, 1527 (2003).}. In this work, the 83.3 $\mu$m region of \chem{ClONO_2} has been recorded at high resolution (0.001 \wn) using a Fourier transform spectrometer and the SOLEIL synchrotron light source. The spectrum corresponds to the absorption of the torsional mode, \nub{9} around 123 \wn and a series of \textit{n}\nub{9}-(\textit{n}-1)\nub{9} hot bands. In this talk, the analysis of the \nub{9} bands of $^{35}$\chem{ClONO_2} and $^{37}$\chem{ClONO_2} and 2\nub{9}-\nub{9} band of $^{35}$\chem{ClONO_2} will be presented. In turn, this will enable an analysis of the hot bands involving low energy levels in the mid-IR region where \chem{ClONO_2} is detected and modelled