Triplet state spectroscopy and photofragment dynamics of Nz+

The photofragment spectrum of N: + + N + (‘Ps ) + N + (‘Ps ) has been studied using a coaxial laser-ion beam spectrometer. Transitions from the excited 38,+ (u = 0,l) state of Nz + to the predissociative 3111, (L, = 0) state result in two bands with dense rotational structure at 15 300 and 13 100 cm ‘. A complete analysis of the 27 rotational branches associated with the 311,(u=o)+ “2: (U = 0) transition provides bond lengths and spectroscopic constants for both states. A perturbation is observed in the (0,O) band, caused by the interaction of ‘LX,.? (u = 0) with 311U ( uz 10). From a deperturbation analysis, the coupling constants and the energy difference between the 311u (u=: 10) and ‘Z,+ (U = 0) states are determinedc= 1.5 f 0.1 cm-‘, r] = 0.220 f 0.003 cm-‘, and r,, = 365 f 25 cm-‘. A broad unstructured band at 16 400 cm ’ arises from a transition out of u = 0 in the 38,+ state into a very short-lived u = 1 level of the 311g state. Vibrational spacings between u = 0 and u = 1 in both electronic states are determined-‘2: o0 = 2210 f 20 cm ’ and 311, w,, =: 1100 cm ‘. The fragmentation of N$ + is explored by measuring the dependence of predissociation lifetimes on the rotational quantum number of the 311, (u = 0) state. Experimentally determined lifetimes of 50-70 ps for N’ = 2-17 are almost independent of N’ and indicate that the predissociation occurs by the interaction of 311, (u = 0) with the ‘Z; continuum rather than by tunneling through the 311s barrier.