Herzberg continuum cross section of oxygen in the wavelength region 193.5-204.0 nm: New laboratory measurements and stratospheric implications

Abstract

The absorption cross section of oxygen at 300 K and at pressures in the range 50-760 torr has been measured throughout the wavelength region 193. 5-204. 0 nm with a 6. 65 m scanning spectrometer having an instrumental full width at half maximum of 0. 0013 nm. The absorption features in this region are the discrete lines of some Schumann-Runge bands and two underlying dissociation continua, viz. , the weak Herzberg continuum of oxygen and a pressure dependent continuum involving two molecules of oxygen. At all wavelengths in this region, the values of the Herzberg continuum cross section are smaller than previous laboratory values, much smaller than values used in many photochemical models, and consistent with recent in situ stratospheric values. The acceptance of reduced Herzberg continuum cross sections implies significant changes in photochemical modelling predictions of the stratospheric concentrations and altitude profiles of ozone, chlorofluorocarbons and nitrous oxide.