Collision-induced absorption in the region of the O2 fundamental:: Bandshapes and dimeric features

The oxygen fundamental collision-induced absorption bandshapes are simulated for temperatures between 90 and 296 K. It is shown that the use of line-mixing formalism allows nice simulation of the observed bandshapes including minor regular ripples superimposed on the smooth continuum in the region of the S and O branches. Weak absorption due to tightly bound oxygen dimers manifests itself as pseudodiatomic PR-like structure atop the monomer O branch. Consideration of the temperature variations of this structure allows the oxygen-dimer effective rotational constant [B] to be roughly characterized. The value of [B] is notably lower than the ground state value B-0 retrieved recently by high-resolution laser probe of oxygen dimers formed in a supersonic slit expansion. This may be considered an indication of significant deviation of the (O-2)(2) structure averaged over the ensemble of thermally excited dimers from that characterizing the ground state, (C) 2000 Academic Press.