Investigation of the collision‐induced absorption by O2 near 6.4 μm in pure O2 and O2/N2 mixtures

Abstract

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 = SO2‐O2 ρO22 + SO2‐N2 ρO2 ρN2, where SO2‐O2 and SO2‐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 SO2‐O2 = 6.972(66) × 10−4 cm−2 and SO2‐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., SO2‐O2 = 6.972(66) × 10−4 cm−2 amagat−2 and SO2‐N2 = 7.12(22) × 10−4 cm−2 amagat−2).