DISSOCIATION OF STATE-SELECTED NO2-PHOTOION COINCIDENCE TECHNIQUES( IONS STUDIED BY THRESHOLD PHOTOELECTRON)

Fragmentation patterns and dissociation rates of state-selected NO2+ i ons were measured by the threshold photoelectron-photoion coincidence (TPEPICO) method in the region of 40-100 nm. Parent NO2+ ions were det ected when they were prepared in the excited states located above the first dissociation limit (D-0(0) = 2.79 eV), correlating to NO+(X(1) S igma(+)) + O(P-3). Specially, the dissociation rate (k(dis)) of NO2+ i ons in the lowest excited <(a)over tilde B-3(2)> State increases with increasing the quantum number of the bending vibration (n(2)): (7.4 +/ - 4.9) x 10(2), (1.32 +/- 0.56) x 10(3), (1.51 +/- 0.40) x 10(4), and (2.38 +/- 0.51) x 10(4) s(-1) for n(2) = 0, 1, 2, and 3, respectively. The branching ratios of two dissociation pathways, NO+ + O and O+ + N O, were found to depend on the electronic state of the parent ion. The unimolecular dissociation channels are discussed in terms of dissocia tion potential surfaces open for individual electronic states and radi ative relaxation to lower electronic states.