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Ab initio cross section calculations for vibronic excitation using the R-matrix approach have been performed on the N2+ molecular ion complex. A three-state close-coupling expansion is used where the electronic target states; X 2g+, A 2u and B 2u+ of the molecular cation are represented by a valence configuration-interaction approximation. A non-adiabatic approximation is invoked to study vibronic excitation for the first three negative bands, (0,0), (1,0) and (2,0) of the X-B transition (B 2u+v´X 2g+v´´) of N2+. Fixed-nuclei and non-adiabatic cross section results are compared with the available experimental data for the (0,0) band and the breakdown of the adiabatic fixed-nuclei approximation is clearly evident for the vibronic excitation of the (1,0) and (2,0) bands in this molecular ion complex.

Ab initio electron scattering calculations using the R-matrix approach have been performed for N + 2 within a three-state valence configuration-interaction model (VCI). The lowest three electronic target states (X 2 + u , A 2 u and the B 2 + u ) of this molecular nitrogen cation are included in the close-coupling method, with each state being represented by a valence CI approximation. From a detailed analysis of the resonance structure found in our work for the 1,3 + g symmetries we find four prominent Rydberg series of the type npπ u , nfπ u , npσ u , nfσ u and a 2pσ u interloper resonance. This 2pσ u interloper molecular resonance associated with the B state of N + 2 is seen to cause distortions of the resulting resonance spectra. A comparison of our total cross sections for the X-B transition shows excellent agreement with the available experimental data.Electron collisions with molecular ions play a fundamental role in laboratory and astrophysical plasmas with the dissociative recombination process being the main mechanism for the removal of ions. The 0-0 band of the first negative system of N + 2 at approximately 391.4 nm (X-B transition) is an extremely intense emission band and is widely used in many diagnostic measurements. It is possible that, during severely disturbed conditions, electron impact excitation of molecular oxygen and nitrogen ions could be important, for example during space vehicle re-entry, but not under normal conditions (Dalgarno 1997). Ionization of the neutral parent is a more likely source of ions as indicated in recent experiments (Doering and Yang 1997a, b). What prompted us to study this system was the fact that the molecular nitrogen ion and its neutral are of importance in the atmosphere of our planet, not least in the study of flow fields surrounding high-velocity space vehicles at re-entry. In this complex, specifically for the X-B transition, there has been early experimental work performed on this system (Crandall et al 1974, Lee and Carleton 1968, Dashchenko et al 1973 and more recently theoretical studies using the complex Kohn method (Orel et al 1990). To the best of our knowledge there has been no detailed study of resonances arising in the case of electron-collisional excitation of this molecular ion complex. Such a study will provide a wealth of electronic and vibrational information which can provide a doorway to other transient molecular processes. Knowledge of the resonance positions and widths, as a function of the internuclear geometry can be used as input to various theories of field-free and laser-assisted, associative (AI) and Penning (PI) ionization. The present work is an initial attempt to provide information and identify the relevant resonant molecular processes and their associated parameters.

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