The 1.27 m O2 Continuum Absorption in O2/CO2 Mixtures
Gerald T. Fraser, Walter J. Lafferty
The collision-induced, near-infrared O2 continuum band overlapping the weak α1δg - X3ς-g, v=O -0, 1.27 m discrete band of O2 has been investigated in O2/CO2 mixtures at room temperature (T=296 K) for total densities from 1.8 to 9.3 times that of an ideal gas under standard conditions (T=273.15 K and P =101.325 kPa), i.e., from 1.8 to 9.3 amagats. Absorption spectra were recorded at 0.5 cm-1 resolution using a Fourier-transform spectrometer and an 84-m optical pathlength through the gas sample. A least-squares analysis of the integrated band strength, Stotal = SO2 PO2 =SO2-O2 PO22+SO2-CO2PO2PCO2, as a function of carbon dioxide density, PCO2, and oxygen density, PO2, yields SO2-CO2 = 2.95(40) x 10-43 cm-2(molecule/cm3)-2 [i.e., 2.13(29) x 1004 cm-2 amagat-2]. The SO2-CO2 coefficient is approximately three times greater than the corresponding SO2-N2 coefficient determined from studies of O2/N2 mixtures, illustrating the efficiency of large electric multipolar moments in inducing continuum absorption in the 1.27 m band of O2. Furthermore, the results suggest the potential importance of water, with its large electric dipole moment, in enhancing the collision-induced absorption bands of O2 and N2 in the atmosphere. Indeed, the apparent inability of radiative-transfer models to accurately account for the increased atmospheric absorption present when water-vapor levels increase may be due in part to the neglect of the intensity enhancement of a number of continuum bands and the far wings of discrete bands by water collisions.