15min:

K. WARING, P. M. DOOLEY, B. R. LEWIS, S. T. GIBSON AND K. G. H. BALDWIN, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.

\noindent Predissociation in the Schumann-Runge bands of molecular oxygen plays an important role in the production of atmospheric ozone. However, the region of the Schumann-Runge bands near the dissociation limit (v' = 18 - 22) has only been partially analysed in the past. This has been due to the difficulties associated with obtaining accurate intensity and width measurements with spectrographic techniques, and the presence of ``main" and ``extra" lines associated with rotational perturbations.

\noindent Our use of the non-linear optical technique of four-wave difference-frequency mixing (FWDFM) has enabled this region of the Schumann-Runge bands (from 175-178 nm) to be studied in unprecedented detail, with sub-Doppler resolution in absorption. Recent measurements using FWDFM have enabled analysis of the v' = 16 - 18 bands, with interpretation of the perturbations present in this region. The current investigation involves the study of those lines from v' = 19 - 22. Preliminary analysis of the v' = 19 band rotational lines confirms the presence of perturbations in the F₃ levels, possibly caused by interactions with the C'\,³_u state. Results will be presented here on the recent findings in this region.