Fourier transform spectroscopy of the O-2 Herzberg bands. III. Absorption cross sections of the collision-induced bands and of the Herzberg continuum

Absorption spectra of molecular oxygen were measured in the laboratory unde r temperature and pressure conditions prevailing in the Earth's atmosphere. Spectra of pure O-2, O-2 + N-2, and O-2 + Ar were recorded in the 41 700 t o 33 000 cm(-1) region (240-300 nm) at a maximal optical path difference of 0.45 cm using a Fourier transform spectrometer and a multiple reflection g as cell. The different components of the spectra, namely the discrete bands of the three Herzberg systems, the Herzberg continuum, and the collision-i nduced diffuse Wulf bands, were separated. The contribution of the Herzberg bands was first subtracted using the line parameters determined previously LA. Jenouvrier, M.-F. Merienne, B. Coquart, M. Carleer, S. Fally, A. C. Va ndaele, C. Hermans, and R. Colin, J. Mel. Spectrosc. 198, 136-162 (1999)] f rom high-resolution data. Spectra recorded at various pressures then made i t possible to determine by linear regression the intensity of the Wulf band s and the Herzberg continuum. The characteristics of the Wulf bands have be en investigated in details: vibrational analysis, pressure effect, foreign gas effect, and a simulated spectrum are reported. The Herzberg continuum c ross section is determined below the dissociation limit. A comparison with literature data is given. The new O-2 absorption cross sections and O-2-O-3 collision-induced absorption cross sections are useful in connection with atmospheric measurements of ozone and other trace gases in the UV spectral region. (C) 2000 Academic Press.