Collision-Induced Absorption in the Region of the O2 Fundamental: Bandshapes and Dimeric Features

Abstract

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 Q 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 B0 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 (O2)2 structure averaged over the ensemble of thermally excited dimers from that characterizing the ground state.