Absolute intensities for the O2 1.27 μm continuum absorption

Abstract

Collision‐induced absorption coefficients for the 1.27 μm band of O2 have been measured at a resolution of 0.5 cm−1 and an optical path length of 84 m using a Fourier transform spectrometer. Spectra were recorded for sample densities ρ from 1 to 10 times that of an ideal gas under standard conditions (T = 273.15 K and P = 101.325 kPa) at temperatures of 253, 273, and 296 K for pure O2 and O2/N2 mixtures. After removing the contributions from the sharp lines of the υ = 0 ← 0 component of the O2 a1Δg ← X3∑g− band, which overlaps the continuum band, the integrated band strength per unit path length, S ≡ SO2−O2ρO22 + SO2−N2ρN2ρO2, has been determined for several values of the densities, ρO2 and ρN2, to give values for SO2−O2 and SO2−N2. At 296 K we find SO2−O2 = 4.847(22) × 10−43 cm−2 (molecule/cm3)−2 and SO2−N2 = 0.941(50) × 10−43 cm−2 (molecule/cm3)−2. Type A standard uncertainties are given, that is, ±1σ, from a least squares analysis of the integrated‐intensity‐versus‐density data. The SO2−O2 coefficient is in reasonable agreement with the previous measurements of Cho et al. [1963]; however, our value for SO2−N2is 2.6 times greater than their results. Our derived air coefficient SO2−air is 37% greater than the atmospheric value of Mlawer et al. [1998], after correcting their continuum value for an updated value for the absorption coefficients for the overlapping discrete structure of the O2a1Δg ← X3∑g− band.