## Calculated potential energy curves for the m ^1Sigma ^+_g symmetry

**Figure 4.** Calculated potential energy curves for the \rm ^1\Sigma ^+_g symmetry. Coloured are the Rydberg series nsσ_{g}, ndσ_{g} and ngσ_{g} as well as A ^{2}Π_{u}(3pπ_{u}) and valence states \rm a^{\prime \prime }\:{^1}\Sigma _g^+ and 2\:{^1}\Sigma _{\rm g}^+. The lowest state in the ndσ_{g} series is that assigned by Cossart and Cossart-Magos (2004) to be \rm d_3\;{}^1\Sigma ^+_g.

**Abstract**

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 N_{2} with *n* ≤ 6 and ℓ ≤ 4 as well as many higher states including some Rydberg states associated with the first excited A ^{2}Π_{u} state of N_2^+. 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 N_{2}.