## ABSOLUTE INTENSITIES FOR THE $O_{2} 1.27 \mu$m CONTINUUM ABSORPTION

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### Date

1999

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Ohio State University

### Abstract

Collision-induced absorption coefficients for the $1.27 \mu$m band of $O_{2}$ have been measured at a resolution of $0.5 cm^{-1}$ 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 $O_{2}$ and $O_{2}/N_{2}$ mixtures. After removing the contributions from the sharp lines of the $v = 0 \leftarrow 0$ component of the $O_{2} a^{1}\Delta_{g} \leftarrow X^{3}\Sigma_{g}^{-}$ band, which overlaps the continuum band, the integrated band strength per unit pathlength, $S\equiv S_{O_{2}-O_{2}} \rho_{O_{2}}^{2}+S_{O_{2}-N_{2}}\rho_{N_{2}} \rho O_{2}$, has been determined for several values of the densities, $po_{2}$ and $\rho N_{2}$, to give values for $S_{O_{2}-O_{2}}$ and $S_{O_{2}-N_{2}}$. At 296 K we find $S_{O_{2}-O_{2}} = 4.847(22) \times 10^{-43} cm^{-2}$ (molecule/$cm^{3})^{-2} [3.499(16) \times 10^{4} cm^{-2} amagat^{-2}]$ and $SO_{2}-N_{2} = 0.941(50) \times 10^{-43} cm^{-2} (molecule/cm^{3})^{-2} [0.679(36) \times 10^{-4} cm^{-2} amagat^{-2}]$. Here and elsewhere, Type A expanded uncertainties are given with a coverage factor $k = 2$. The $SO_{2}-O_{2}$ 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 $S_{O_{2}-N_{2}}$ is a factor of 2.6 times greater than their results. The derived air coefficient, $S_{O_{2}-N_{2}}$, 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 $O_{2} a^{1} \Delta_{g} \leftarrow X^{3}\Sigma_{g}$ band. The binary collision coefficients are available as a function of frequency for use in atmospheric modeling.

### Description

Author Institution: Optical Technology Division, National Institute of Standards and Technology