O-2 HERZBERG CONTINUUM ABSORPTION CROSS-SECTIONS IN THE WAVELENGTH REGION 196-205 NM OF THE SCHUMANN RUNGE BANDS

New laboratory measurements of the absorption cross-sections in the Herzberg continuum of oxygen have been performed at 219 K in the wavelength region 196-205 nm of the first Schumann Runge bands. Owing to the temperature, measurements between the lines, even with moderate resolution (0.065 nm), provide accurate cross-sections after subtracting the SR line contributions. These values are in agreement with previous determinations (Cheung et al., 1984, Can. J. Phys. 62, 1752; Cheung et al., 1986, Planet. Space Sci. 34, 1007; Ogawa, 1971, J. chem. Phys. 54, 2550) within their respective quoted uncertainties and are particularly in line with the last improved data of Yoshino et al. (1988, Planet. Space Sci. 36, 1469) obtained at room temperature in the region 205-240 nm. The whole shape of the continuum is described by a formula similar to that of Johnston et al. (1984, J. geophys. Res. 89, 11661). The maximum of the absorption cross-section (~8.1 × 10-24 cm2) is thus obtained at 197 nm, close to the value of 7.8 × 10-24 cm2 given by Johnston but slightly different from that (6.6 × 10-24 cm2) proposed by Cheung et al. (1986). Calculation of the absorption in the continuum from computed Franck Condon densities leads to a transition moment in good agreement with ab initio results of Klotz and Peyerimhoff (1986, Molec. Phys. 57, 573). The present laboratory cross-sections are consistent with in situ stratospheric cross-sections determined in the region 200-220 nm. © 1990.