## Edlén plots for
m ^{1}B_{2u} symmetry: (a) effective quantum numbers calculated relative to the ground state,
m X:^1Sigma _g^+; (b) relative to the first excited state A ^{2}Π_{u}

**Figure 3.** Edlén plots for \rm ^{1}B_{2u} symmetry: (a) effective quantum numbers calculated relative to the ground state, \rm X\:^1\Sigma _g^+; (b) relative to the first excited state A ^{2}Π_{u}. Effective quantum numbers of Rydberg states are nearly constant with *R* if calculated relative to the state they are converging upon and so appear as straight lines on the plot. The red curve illustrates the behaviour of the A ^{2}Π_{u}(3sσ_{g}) state in the two cases.

**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}.