An upper limit for the absorption cross section of the oxygen transition

A search was made for absorption by O 2 (a¹Δ g ) in the wavelength region 190–290 nm. Measurements were done at 10 nm intervals with a grating spectrometer having a bandwidth of 9.0 nm. No absorption above the detection limit of 0.02–0.03% absorption could be observed for O 2 (a¹Δ g ) concentrations of (4–7) × 10 15 cm −3 . An upper limit of 8×10 −22 cm² for the absorption cross section of O 2 (a¹Δ g ) in this wavelength region was calculated.