Potential energy curves for electronically excited states of molecular nitrogen are calculated using three different ab initio procedures. The most comprehensive of these involves the use of scattering calculations, performed at negative energy using the UK molecular R-matrix method. Such calculations are used to characterize all the Rydberg states of N2 with n ⩽ 6 and ℓ ⩽ 4 as well as many higher states including some Rydberg states associated with the first excited A 2Πu state of N. Many of these states are previously unknown. The calculations are performed at a dense grid of internuclear separations allowing the many avoided crossings present in the system to be mapped out in detail. Extensive comparisons are made with the previously available data for excited states of N2.

Resonant vibrational excitation cross sections and the corresponding rate coefficients for electron-N 2 collisions occurring through the N − 2 (X 2 Π g ) resonant state are reviewed. New calculations are performed using accurate potential energies curves for the N 2 electronic ground state, taken from literature, and for the N − 2 resonant state, obtained from R-matrix calculations. The calculations are extended to resonant excitation processes involving the N 2 ground state vibrational continuum, leading to dissociation. Electron impact dissociation is found to be significant from higher vibrational levels. Accurate analytical fits for the complete set of the rate coefficients are provided.The behavior of the dissociative cross sections is investigated for rotationally excited N 2 molecules, with J = 50, 100 and 150 and for different vibrational levels.

Cross sections for the dissociative recombination of N + 2 for v + i = 0-3 are computed using multichannel quantum defect theory with molecular data generated using the R-matrix method. The calculation is completely ab initio and includes three electronic cores of the ion. Extensive comparisons are made with previous experimental and theoretical studies. Our cross section is in excellent agreement with experimental results and other theoretical results. Cross sections and isotropic rate coefficients are provided for all computed vibrational levels.

A systematic calculation of the positions and widths of the resonances converging on the first two excited states of N + 2 (A 2 u and B 2 + u ) is presented. A closely-spaced grid of geometries is used to give continuous resonance curves without the need for curve fitting. Three methods, fitting the eigenphase sum, the time-delay method and the R-matrix specific QB method, are tested. Fits to the longest three time-delays are found to give the most reliable and complete determination of the resonance parameters. The low excitation energies of the A and B ion states results in complex resonance features with many avoided crossings leading to pronounced structures in both the resonance curves and the associated widths. The resonance curves likely to be important for dissociative recombination are identified. Their positions generally agree well with the calculations of Guberman, although in some cases their widths are narrower. Full data on all curves is provided.

We compute molecular continuum orbitals in the single center expansion scheme. We then employ these orbitals to obtain molecular Auger rates and single-photon ionization cross sections to study the interaction of N 2 with Free-Electron-Laser (FEL) pulses. The nuclei are kept fixed. We formulate rate equations for the energetically allowed molecular and atomic transitions and we account for dissociation through additional terms in the rate equations. Solving these equations for different parameters of the FEL pulse, allows us to identify the most efficient parameters of the FEL pulse for obtaining the highest contribution of double core hole states (DCH) in the final atomic ion fragments. Finally we identify the contribution of DCH states in the electron spectra and show that the DCH state contribution is more easily identified in the photo-ionization rather than the Auger transitions.