15min:

S. VOIGT, S. DREHER, J. ORPHAL AND J. P. BURROWS, Institute of Environmental Physics, University of Bremen, PO Box 330440, D-28334 Bremen, Germany.

N₂ induced pressure broadening in the ¹³C¹⁶O 2--0 band around 4167 cm^-1 was investigated using Fourier Transform Spectroscopy. The spectra were recor\-ded with a sample of 99 % isotopically pure ¹³CO in a White-type absorption cell at a resolution of 0.005 cm^-1. Voigt profiles convolved with the FTS apparatus function were fitted to the observed lineshapes, and Lorentzian HWHM were determined as function of N₂ pressure. Pressure broadening coefficients for m between --33 and +34 were obtained with uncertainties of 5.8 %.. The results are compared to N₂ broadening coefficients obtained from simultaneous measurements in the 2--0 band of ¹²C¹⁶O.

While the latter values agree well with those published earlier, those of ¹³C¹⁶O are systematically lower by 5--7 % compared to ¹²C¹⁶O. This indicates that in spectroscopic databases the pressure broadening of ¹³C¹⁶O is significantly overestimated. This is most important since recent work shows that the ¹³CO/¹²CO mixing ratio is an indicator of stratospheric O₃ depletion chemistry.