The N + Formation Mechanism of Vibrationally Selected N 2 O + Ions in the C 2 Σ + State: A TPEPICO Imaging Study.

The N-NO bond fission of N 2 O + (C 2 Σ + ) ions can produce two major fragment ions, NO + or N + . In contrast to the dominant NO + fragment ion, the N + formation mechanism remains unclear to date. Here, dissociative photoionization of N 2 O via the C 2 Σ + ionic state has been reinvestigated using a combined approach of threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging and quantum chemical calculations. Accompanying the N + ( 3 P) formation, the NO(X 2 Π) neutral fragment with low and high vi-rotational distributions was identified, based on the N + speed and angular distributions derived from the TPEPICO images. In particular, the excitation of the symmetric stretching ν 1 + mode promotes the formation of high rotational components, while the asymmetric stretching ν 3 + mode shows the exact opposite effect. According to our calculated multistate potential energy surfaces, intersystem crossing from C 2 Σ + to 1 4 Π exclusively provides feasible decomposition pathways to produce the N + fragment. In a slightly bent geometry, spin-orbit couplings between C 2 Σ + and two substates of 1 4 Π, 1 4 A' or 1 4 A″, play a crucial role in the N + formation from vibrationally selected N 2 O + (C 2 Σ + ) ions. The mechanism also provides new insights into the charge transfer reaction of N + + NO → N + NO + .