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.
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The collision-induced fundamental vibrational band of molecular oxygen has been measured between 1300 and 2000 cm−1 using a Fourier-transform infrared spectrometer and an optical path length of 84 m. Spectra were recorded for pure O2 and O2/N2 mixtures at densities up to 10 times the density of an ideal gas at standard temperature (273.15 K) and pressure (101.325 kPa), and for temperatures between 228 and 296 K. The band is dominated by the ΔJ = 0, Q branch and the ΔJ = 2, S and ΔJ = −2, O branch shoulders, with the S branch exhibiting ripples previously attributed to bound dimer transitions, pure quadrupole transitions of O2 perturbed by line mixing, and intercollisional interferences. The ripples are seen at the same wavenumbers in O2-Ar mixtures, with intensities dependent on both the O2 and Ar densities, suggesting that the ripples are not due to bound dimer transitions. The integrated band intensity S is related to the collision-induced absorption coefficients by S = S O 2 - O 2 ρ O 2 2 + S O 2 - N 2 ρ O 2 ρ N 2 , where S O2-O2 and S O2-N2 are the integrated binary collision-induced absorption coefficients for O2-O2 and O2-N2 collisions, respectively, and ρO2 and ρN2 are the O2 and N2 gas densities. We find values for S O2-O2 = 6.972(66) × 10−4 cm−2 and S O2-N2 = 7.12(22) × 10−4 cm−2, respectively, at 296 K, when the gas density is equal to that found at STP (i.e., S O2-O2 = 6.972(66) × 10−4 cm−2 amagat−2 and S O2-N2 = 7.12(22) × 10−4 cm−2 amagat−2).
