A surface chemistry model for the altitude dependence of the N2 Lyman-Birge-Hopfield glow on spacecraft

Low-orbiting spacecraft have been observed to cause UV emission in the N2 Lyman-Birge-Hopfield bands. The chemical processes expected to underlie this emission are examined. Recombination between incident and adsorbed N atoms has been proposed as the source of radiating excited N2. However, the cubic dependence of the intensity, as N2 concentration cubed or N2 concentration squared x O concentration, has not been explained. It is suggested that this can be explained by a model where adsorption of nitrogen on the spacecraft surface is balanced mainly by the removal of N from the surface by atomic oxygen. On the basis of these assumptions a mathematical model for the production of excited N2 is constructed. It is shown that for large enough reaction efficiencies the model predicts a magnitude and altitude dependence for the emission which can explain the measurements reported by other investigators.