The $v_{4}$ band of Carbonyl fluoride.

Author Institution: LPMA, Bte 76, T13, CNRS, Universit{\'e} P. et M. Curie,; Physics Department, University of Denver, Denver; Atmospheric Sciences Division, NASA Langley Research Center$COF_{2}$ which has been postulated to be an important intermediate in the decomposition of chlorofluorocarbons in the upper atmosphere has been observed in the stratosphere through the identification of absorption features of its $^{v}6$, $^{v}4$ and $^{v}1$ bands by the ATMOS experiment. In addition, recently the $^{v}6$ and$^{v}4$ bands have been observed at very high resolution ($0.002 cm^{-1}$) using a balloon borne FTS (Denver University group). Since in order to analyse the atmospheric spectra it is necessary to know precisely the spectral parameters of the molecule, we have undertaken, using $0.002 cm^{-1}$ resolution laboratory spectra, an extensive analysis of the $^{v}4$ band of COF2. It proved not possible to reproduce correctly the observed wavenumbers considering the $^{v}4$ = 1 state as isolated and it was necessary to take into account the nearby state located about 4 $cm^{-1}$ below. In this way the line positions were reproduced within their experimental uncertainty allowing to determine accurate band centers and rotational and coupling constants. Comparisons between a calculated and the experimental spectrum will be presented showing the quality of the results