Effects of Bending and Bending Angular Momentum on Reaction of NO<sub>2</sub><sup>+</sup> with C<sub>2</sub>H<sub>2</sub>: A Quasi-Classical Trajectory Study

A large set of quasi-classical trajectories were calculated at the PBE1PBE/6-311G** level of theory, in an attempt to understand the mechanistic origins of the large, mode-specific enhancement of the O-transfer reaction by NO<sub>2</sub><sup>+</sup> bending vibration and the surprisingly large suppressing effect of bending angular momentum. The trajectories reproduce the magnitude of the absolute reaction cross section, and also get the dependence of reactivity on NO<sub>2</sub><sup>+</sup> vibrational state, and the vibrational state dependent scattering behavior qualitatively correct. Analysis of the trajectories shows that the bending effect is not simply a consequence of enhanced reactivity in bent geometries but, rather, that excitation of bending motion allows reaction in a wider range of orientation angles, even if the NO<sub>2</sub><sup>+</sup> is not bent at the onset of the collisional interaction. There is a strong interplay between NO<sub>2</sub><sup>+</sup> bending and transient charge transfer during the collisions. Such charge transfer enhances reactivity, but only if the reactants are oriented correctly.