Laser-induced fluorescence from nascent N2+(X 2Σg+) ions produced by electron impact on a N2 supersonic beam was observed. An analysis of the B 2Σu+-X 2Σ g+ (0,0) band shows that the rotational state distributions cannot be represented by a single Boltzmann function, higher N″ levels being overpopulated. Experimental and analytical efforts were made to minimize the influence of cascading and relaxation on the rotational distributions. The rotational energy of N2+ (X) thus estimated increases with decreasing electron energy from 2.26±0.16 meV at 300 eV to 4.24±0.27 meV at 25 eV. This trend is explained qualitatively in terms of angular momentum transfer through multipole electron-molecule interactions.
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