A surface chemistry model for the production of N 2 LBH spacecraft glow

Abstract

Spacecraft-atmosphere interactions leading to N 2 Lyman-Birge-Hopfield (LBH) bands in the 1400–1700 Å ultraviolet (reported by Conway et at., 1987, Geophys. Res. Lett. 14, 628) have been proposed to result from surface recombination of N (Kofsky, 1988, Geophys. Res. Lett. 15, 241; Swenson and Meyerott, 1988, Geophys. Res. Lett. 15, 245). The surface recombination of N( 4S) can populate the a 1Π g , state (which leads to N 2 LBH emission) either (1) directly, or (2) by cascade from higher excited states of N 2. Gas phase recombination produces a 1Π q populations in υ = 4−6, whereas the observed spacecraft surface interactions lower the vibrational population. This study describes and explores the possible cascade (2) mechanism where the upper states of N 2 (particularly c′ 4 1 Σ + u ) are populated with the translational energy of ramming N on surface bound N, in recombination. The cascade mechanism would populate the a 1 Π g , υ = 0–1 directly. The proposed cascade mechanism predicts additional emissions at ∼ 3000 A ̊ (Gaydon Herman band system) and ∼ 958 A ̊ from the surface recombination. The 958 Å photons can resonant scatter in the spacecraft cloud and atmospheric N 2 which would result in extended spacecraft glows in low Earth orbit. The altitude profile is predicted and compared with observations. The predicted emissions offer criteria for experimental confirmation of the (1) “direct” vs (2) “cascade” mechanisms.