NO+ formation pathways in dissociation of N2O+ ions at the C2Σ+ state revealed from threshold photoelectron-photoion coincidence velocity imaging.

Using the novel threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging technique, the dissociative photoionization of N(2)O molecule via the C(2)Σ(+) ionic state has been investigated. Four fragment ions, NO(+), N(2)(+), O(+), and N(+), are observed, respectively, and the NO(+) and N(+) ions are always dominant in the whole excitation energy range of the C(2)Σ(+) ionic state. Subsequently, the TPEPICO three-dimensional time-sliced velocity images of NO(+) dissociated from the vibrational state-selected N(2)O(+)(C(2)Σ(+)) ions have been recorded. Thus the kinetic and internal energy distributions of the NO(+) fragments have been obtained directly as the bimodal distributions, suggesting that the NO(+) fragments are formed via both NO(+)(X(1)Σ(+)) + N((2)P) and NO(+)(X(1)Σ(+)) + N((2)D) dissociation channels. Almost the same vibrational population reversions are identified for both dissociation pathways. Interestingly, the obtained branching ratios of the two channels exhibit some dependence on the excited vibrational mode for N(2)O(+)(C(2)Σ(+)), in which the excited asymmetrical stretching potentially promotes dissociation possibility along the NO(+)(X(1)Σ(+)) + N((2)D) pathway. In addition, the measured anisotropic parameters of NO(+) are close to 0.5, indicating that the C(2)Σ(+) state of N(2)O(+) is fully predissociative, indeed, with a tendency of parallel dissociation, and therefore, the corresponding predissociation mechanisms for the N(2)O(+)(C(2)Σ(+)) ions are depicted.