Formation and electron-ion recombination of N4+ following photoionization in near-atmospheric pressure N2

The time dependent behavior of molecular nitrogen ions has been investigated following pulsed photoionization of near atmospheric pressure N(2) using multiphoton laser techniques and kinetic modeling. Multiple fluorescence bands, some unreported previously, with various temporal behaviors were observed after ultraviolet laser photoionization of N(2)(X (1)Sigma(g)). The initial N(2) ionization was generated via resonance-enhanced multiphoton ionization with focused radiation in the 275-290 nm range, where several resonant transitions are accessible. The observed optical fluorescence bands appeared to be unique to the near-atmospheric pressure N(2) condition and were shown by the evidence in this work to be the result of collisional formation and recombination of N(4)(+). Measured time dependent fluorescence spectra during and after pulsed laser photoionization of N(2), together with a coupled rate equation model, allowed for the determination of the absolute densities of N(2)(+) and N(4)(+) as these species evolved.