The dissociative recombination of N 2+ ( v = 0, 1) as a source of metastable atoms in planetary atmospheres

Abstract

The yield of metastable nitrogen atoms in dissociative recombination of N 2 + ( v = 0, 1)ions has been tudied for different experimental conditions. In a first experiment, the branching ratio for N( 2D) production was directly measured as being higher than 1.85; for N 2 + ( v = 0) this implies that 2D + 2D is the main reaction channel; for N 2 + ( v = 1) a minor channel could be 2P + 2D, 2P being then quenched toward 2D by electrons. In a second experiment, at higher electron densities, the influence of superelastic collisions was studied; a steady state analysis yields the quenching rate coefficient k 4, of 2D towards 4S equal to 2.4 × 10 −10 cm 3 s −1for T e = 3900 K and shows that 2D + 2D is always the major channel of the reaction for N 2 + (v = 1), 2D + 2P being a minor channel. All these results are in good agreement with thermospheric models but imply that N 2 + dissociative recombination is a less important source for nitrogen escape of Mars.