EUV airglow during active solar conditions: 2. Emission between 530 and 930 Å

Daytime airglow spectra between 530 and 930 A were obtained at ∼4 A resolution from a rocket launch at White Sands, New Mexico, June 27, 1980. Portions of the spectrum were observed in second order at ∼2A resolution. The higher resolution of the present data confirms our previous identification of O II transitions and resolves the identification of O II emission at 537–539 A as due to both a doublet and a quartet component. For the case of viewing at 90° to the zenith between 196 and 242 km ∼1/3 of the 537-539 A emission originates from the O II 2s 2p4 ²P state. We infer a 538/581 A branching ratio of ∼ 3 in agreement with laboratory and calculated values of 1.6 to 3.3. Other O II branching ratios are in agreement with laboratory data. A somewhat low value for the 718/796 ratio in the flight data is interpreted as due to blended N2 emission at 796 A. The observed emission rate from the 2s 2p4 ²P state is more adequately modeled using partial photoionization cross sections calculated using the dipole velocity rather than the dipole length approximation. This fact must be considered when computing the 834 A emission rate from direct photoionization. N II is seen to be a very minor source of emission below 916 A in the dayglow. The identification of O II 581 A emission confirms a prediction made in 1977 by Delaboudiniere. The O II emission at 581 A complicates interpretation of low resolution spectral observations near 584 A in the airglow and also for the case of comets and planets where O atoms and O bearing molecules are present.

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