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Calculation of O2 AB emission from OH(v = 9) + O
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A previously unrecognized source of the O2 Atmospheric band emission in Earth’s nightglow

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The steps that control the generation of O2 AB emission from OH(v = 9) + O collisions can be summarized in reactions M1 to M9. Process M4, loss by atmospheric species, includes inelastic scattering and reaction with O atoms that leads to O2 and hydrogen atoms (31). Process M5 is the key step that generates O(1D) and effectively couples the OH Meinel and the O2 AB emissions. Loss of O(1D) by ground-state O atoms is negligible for the altitude range considered here (34)$O+O2+M→O3+M(M=O2,N2,O)$(M1)$H+O3→OH(v=9)+O2$(M2)$O3+O→O2+O2$(M3)$OH(v=9)+M→products(M=O2,N2,O)$(M4)$OH(v=9)+O(3P)→OH(v=3)+O(1D)$(M5)$O(1D)+N2→O(3P)+N2$(M6)$O(1D)+O2→O2(b,v=0,1)+O(3P)$(M7)$O2(b,v=1)+O2→O2(b,v=0)+O2$(M8)$O2(b,v=1)+O→O2(b,v=0)+O$(M9)

We applied the steady-state approximation to chemical species O(1D), OH(v = 9), and O3. The assumption of photochemical equilibrium in the mesosphere is often used in the literature (12, 3537). It is a reasonable approximation for this case that concerns rapid, local measurements of slowly varying nightglow emissions. The steady-state concentration of OH(v = 9) and O2(b, v = 0) generated from source (M5) is described by the equations(M10)(M11)where [M] = [O2] + [N2] + [O]. The yields yi and rate constants ki are listed in Table 1. The factors LT represent the loss terms for OH(v = 9), O2(b, v = 0), O3, and O(1D), respectively(M12)(M13)(M14)(M15)

Ai are the relevant radiative decay rates for O(1D), the (0-0) band of the O2 AB emission, the total emission from O2(b, v = 0), and OH(v = 9), with values 0.009, 0.079, 0.083, and 173 s−1, respectively (31, 38, 39). The observed volume emission rate for an atmospheric species at the altitude of interest is given by the product of its radiative decay rate and number density.

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