Knowledge Bank

Collision-induced absorption coefficients for the $1.27\mu$m band of $O2$ have been measured at a resolution of $0.5cm-1$ and an optical pathlength of $L=84$ m using a Fourier-transform spectrometer and 2-m long White-type multipass absorption cell. Spectra were recorded for sample densities, p, from 1 to 10 times that of a ideal gas under standard conditions ($T=273.15$ K and P = 101.325 kPa), i.e., 1 to 10 amagats, at temperatures of 253 K, 273 K, and 296 K, for pure $O2$ and $O2/N2$ mixtures. After removing the contributions from the sharp lines of the $v=0\leftarrow 0$ component of the $O2a1\Delta g\leftarrow X3\Sigma g-$ band, which overlaps the continuum band, the integrated band strength per unit pathlength, $S\equiv SO2-O2\rho O22+SO2-N2\rho N2\rho O2$, has been determined for several values of the densities, $po2$ and $\rho N2$, to give values for $SO2-O2$ and $SO2-N2$. At 296 K we find $SO2-O2=4.847(22)\times 10-43cm-2$ (molecule/$cm3)-2[3.499(16)\times 104cm-2amagat-2]$ and $SO2-N2=0.941(50)\times 10-43cm-2(molecule/cm3)-2[0.679(36)\times 10-4cm-2amagat-2]$. Here and elsewhere, Type A expanded uncertainties are given with a coverage factor $k=2$. The $SO2-O2$ coefficient is in reasonable agreement with the previous measurements of Cho et al. [C.W. Cho, E.J. Allin, and H.L. Welsh. Can.J.Phys. 41, 1991-2000 (1963)], however our value of $SO2-N2$ is a factor of 2.6 times greater than their results. The derived air coefficient, $SO2-N2$, is 37% greater than the value determined by Mlawer et al. [E.J. Mlawer, S.A. Clough, P.D. Brown, T.M. Stephen, J.C. Landry, A. Goldman, and F.J. Murcray, J.Geophys.Res. 103, 3859-3863 (1998)] from an atmospheric measurement, which has been corrected for the most recent value for the absorption coefficients for the overlapping $O2a1\Delta g\leftarrow X3\Sigma g$ band. The binary collision coefficients are available as a function of frequency for use in atmospheric modeling.