The⁵Σg⁺states of N₂

The electronic structure and energy curves of the 15Σ g + and 25Σ g + states of N2 have been analysed using the multi-configuration self-consistent-field (MC-SCF) method for calculating the wavefunctions and energies. The ab initio model curve for the 15Σ g + state obtains an r e of 1·69 Å and a D e of 825 cm-1. There is also a barrier with a maximum at 2·21 Å with a height of about 800 cm-1 which is a novel feature of this calculation. The potential supports two bound vibrational levels and two shape resonances for J=0. The calculated curve differs most from the semi-empirical curve of Carroll in having a larger r e by about 0·14 Å and a well depth smaller by 250 cm-1. The 5Σ g + curve is known experimentally to predissociate both the B 3Π g and a 1Π g vibration-rotation levels above the dissociation limit. Conversely, two-body radiative association of two N(4 S) atoms is known to occur through the interaction of the 15Σ g + and B and a states. The two-body radiative rates are analysed in terms of the likely spin-orbit interaction between the 15Σ g + and B and a states and the ratio of these rates is calculated under the assumption that the predissociation rate exceeds the radiative in both cases. The ratio of the two-body associative rates kB/ka is calculated to be roughly 20 which is to be compared to an experimental ratio of 32.