Using an ab initio methodology, we compute the potential energy curves and the spinorbit coupling integrals of the N 2 electronic states located in the 0-120000 cm -1 energy domaine.In our analysis, we focus mostly on those located outside the Franck-Condon regio n accessible from the ground state of N 2 i.e. the two strongly bound states 1 3 Σ g -and 1 1 Γ g , and the weakly bound state 2 3 Σ g -, in addition to several repulsive states. We characterize them spectroscopically and we compute their spin-orbit couplings to the close lying singlets, triplets and quintets. This work completes our knowledge on the electronic states of N 2 that may be important intermediates during N + N collisions and for the dynamics of the N 2 singlets and triplets and quintets VUV photodissociation.

The branching ratios for the N(4 S) + N(2 D), N(4 S) + N(2 P), and N(2 D) + N(2 D) channels are measured for the photodissociation of X v J N ; 0, g 2 1 () S  =  + in the vacuum ultraviolet (VUV) region of 100,808-122,159 cm −1 using theVUV-VUV pump-probe approach combined with velocity-map-imaging-photoion detection. No evidence of forming the ground-state N(4 S) + N(4 S) products is found. No potential barrier is observed for the N (2 D) + N(2 D) channel, but the N(4 S) + N(2 P) channel has a small potential barrier of ≈740 cm −1. The branching ratios are found to depend on the symmetry of predissociative N 2 states instead of the total VUV excitation energy, indicating that N 2 photodissociation is nonstatistical. When the branching ratios for N(4 S) + N(2 D) and N(4 S) + N (2 P) products are plotted as a function of the VUV excitation energy for the valence N 2 1 Π u and 1 u S + states, oscillations in these ratios are observed demonstrating how these channels are competing with each other. These data can be used to select both the velocity and internal states of the atomic products by picking the quantum state that is excited. High-level ab initio potential energy curves of the excited N 2 states are calculated to provide insight into the mechanisms for the observed branching ratios. The calculations predict that the formation of both N(4 S) + N(2 D) and N(4 S) + N(2 P) channels involves potential energy barriers, in agreement with experimental observations. A discussion of the application of the present results to astronomy, planetary sciences, and comets is given.

Ab initio calculations are performed at the multireference configuration-interaction level of theory on the diagonal spin-orbit functions for the lowest non-Rydberg states of (3)Pi(u) symmetry in molecular nitrogen. Spin-orbit constants deduced from the ab initio results confirm the recent suggestion, based on new experimental results, that the C (3)Pi(u) state of N(2), long known to be regular in the region of its potential-energy curve minimum, becomes inverted at higher energies. By removing the effects of the crossing C(') (3)Pi(u) state, it is shown that A(v) for the C state changes sign from positive to negative near v=8, corresponding to a change in principal molecular-orbital configuration from (1sigma(g))(2)(1sigma(u))(2)(2sigma(g))(2)(2sigma(u))(3sigma(g))(2)(1pi(u))(4)(1pi(g)) to (1sigma(g))(2)(1sigma(u))(2)(2sigma(g))(2)(2sigma(u))(2)(3sigma(g))(1pi(u))(3)(1pi(g))(2) at an internuclear distance near 1.4 A.