B. MATÉ, C. LUGEZ, G. T. FRASER AND W. J. LAFFERTY, Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899.
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 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, , 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 0 component of the O2 a1 g X3 g- band, which overlaps the continuum band, the integrated band strength per unit pathlength, S SO_2-O_2~ O_22 + SO_2- N_2~ N_2~ O_2, has been determined for several values of the densities, O_2 and N_2, to give values for SO_2-O_2 and SO_2-N_2. At 296 K we find SO_2-O_2 = 4.847(22) × 10-43 cm-2 (molecule/cm3)-2 [3.499(16) × 10-4 cm-2 amagat-2] and SO_2-N_2 = 0.941(50) × 10-43 cm-2 (molecule/cm3)-2 [0.679(36) × 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. \textbf41, 1991-2002 (1963)], however our value of SO_2-N_2 is a factor of 2.6 times greater than their results. The derived air coefficient, SO_2-air, 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. \textbf103, 3859-3863 (1998)] from an atmospheric measurement, which has been corrected for the most recent value for the absorption coefficients for the overlapping O2 a1 g X3 g- band. The binary collision coefficients are available as a function of frequency for use in atmospheric modeling.