Ab initio classical trajectory study of the dissociation of neutral and positively charged methanimine (CH2NHn+ n = 0-2).

The structures and energetics of the reactants, intermediates, transition states, and products for the dissociation of methanimine neutral, monocation, dication, and trication were calculated at the CBS-APNO level of theory. The dissociations of the neutral, monocation, and dication were studied by ab initio direct classical trajectory calculations at the B3LYP/6-311G(d,p) level of theory. A microcanonical ensemble using quasiclassical normal mode sampling was constructed by distributing 200, 150, and 120 kcal/mol of excess energy above the local minima of the neutral, singly, and doubly charged species, respectively. Many of the trajectories dissociate directly to produce H+, H atom, or H2. However, for a fraction of the cases, substantial migration of the hydrogen occurs within the molecule before dissociation. The preferred dissociation product for the neutral and the monocation is hydrogen atom. Elimination of H(2) was seen in 20% of the trajectories for the neutral and in 5% of the trajectories for the monocation. Dissociations of the dication and trication produced H+ rather than H atom. HCNH+ was formed in 85-90% of the dissociating trajectories for the monocation and dication.