15min:
ABSOLUTE INTENSITIES FOR THE O2 1.27 µm CONTINUUM ABSORPTION.

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, rho, 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 O2 a1 Deltag leftarrow X3 Sigmag- band, which overlaps the continuum band, the integrated band strength per unit pathlength, S equiv SO_2-O_2~ rhoO_22 + SO_2- N_2~ rhoN_2~ rhoO_2, has been determined for several values of the densities, rhoO_2 and rhoN_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 Deltag leftarrow X3 Sigmag- band. The binary collision coefficients are available as a function of frequency for use in atmospheric modeling.