Predissociation mechanism for the lowest ¹Π _u states of N ₂

Separate coupled-channel Schrödinger-equation (CSE) models of the interacting ¹Π _u (b,c,o) and ³Π _u (C, C′) states of N2 are combined, through the inclusion of spin-orbit interactions, to produce a five-channel CSE model of the N2 predissociation. Comparison of the model calculations with an experimental database, consisting principally of detailed new measurements of the vibrational and isotopic dependence of the ¹Π _u linewidths and lifetimes, provides convincing evidence that the predissociation of the lowest ¹Π _u levels in N2 is primarily an indirect process, involving spin-orbit coupling between the b ¹Π _u - and C ³Π _u -state levels, the latter levels themselves heavily predissociated electrostatically by the C′ ³Π _u continuum. The well-known large width of the b (v=3) level in N214 is caused by an accidental degeneracy with C (v=9). This CSE model provides the first quantitative explanation of the predissociation mechanism for the dipole-accessible ¹Π _u states of N2, and is thus likely to prove useful in the construction of realistic radiative-transfer and photochemical models for nitrogen-rich planetary atmospheres.