STATE-SPECIFIC PREDISSOCIATION OF N2(B3-PI-G) MEASURED BY LASER-INDUCED FLUORESCENCE ON A MOLECULAR-BEAM

Using sub-Doppler laser induced fluorescence spectroscopy on a beam of metastable nitrogen N2(A 3Σu +), the predissociation of the N2(B 3Π g) state was studied quantitatively and under collision-free conditions. Predissociation rate constants γ in the range 0.1-200 × 106/s were measured (a) from the decreased fluorescence quantum yield and (b) from the increased linewidth. In method (a), coherent saturation effects were quantitatively accounted for. For the 3Π 0e, 3Π1e,f, and 3Π2e,f levels, γ is generally high and independent of the molecular rotation in the range J = 1-8, while for 3Π0f levels γ is smaller and increases proportionally to J(J + 1). This pattern identifies the N2(A′ 5Σg+) state uniquely as being responsible for the perturbation of N2(B). A pronounced dependence of γ on the vibrational level of N2(B) was also found in the range v′ = 13-18. It correlates quantitatively with calculated bound-free Franck-Condon factors between the B and A′ states. For the latter, a recent ab initio potential curve was used, with a slight (0.02 Å) radial adjustment. The B-A′ electronic coupling matrix element is on the order of 2 cm -1, much smaller than expected for a spin-orbit mechanism. This can be understood on the basis of the CI composition of the interacting states as calculated ab initio. © 1990 American Institute of Physics.