Cross section for the production of N 2+ ( X2 Σ g+) ions by electron impact on N 2

Abstract

A combination of electron scattering and laser-induced fluorescence (LIF) techniques has been employed in the direct experimental determination of the N 2 + ( X 2Σ g +) ionization cross section as a function of electron energy from threshold to 200 eV. Electron impact on N 2 produces N 2 + ground-state ions that are detected by pumping the X 2Σ g + → B 2Σ u + (0,0) vibrational transition at 391 nm with a tunable dye laser and detecting the subsequent LIF of the B 2Σ u + → X 2Σ g + (0,1) vibrational transition at 428 nm. LIF spectra obtained at different electron energies yield the relative N 2 +( X) cross section which is put on an absolute scale by normalization to the absolute cross section value of Doering and Yang [J. Geophys. Res. 102 (1996) 9683] obtained from electron–electron coincidence ( e,2 e) experiments at 100 eV.