Vibrational distribution of N2+A ²Πu from 100‐eV electron impact on N2

Measurements of the electron excitation of the Meinel band system of N2+ produced by electron impact on N2 have been hampered by the long lifetime of the N2+ A 2Πu upper state, the spectroscopically inconvenient near‐infrared region where the bands are located, as well as overlap by the N2 first positive system. In the present work, an experiment in which the scattered projectile electron and the low‐energy secondary electron are detected in coincidence was used to allow the vibrational distribution of the A 2Πu state produced by 100‐eV electron impact on N2 to be determined directly in excitation without the need for optical measurements. The coincidence energy loss spectrum was measured for a typical secondary electron energy of 5 eV over a range of secondary electron ejection angles. The results of a band contour analysis show that the population of the ν′=0‐5 vibrational levels is consistent with that predicted by the Frank‐Condon factors for ionization of N2 to the N2+ A 2Πu state.