Quantitative Dynamics of the N2O + C2H2 → Oxadiazole Reaction: A Model for 1,3-Dipolar Cycloadditions

The reaction N2O + C2H2 → oxadiazole has been considered as a prototype for 1,3-dipolar cycloadditions. Here, we report a comprehensive dynamical study of this important reaction on a full-dimensional potential energy surface, which is fitted to about 64 000 high-level ab initio data by a machine learning approach. Comprehensive dynamical simulations are carried out to provide quantitative chemical insight into its reaction dynamics. In addition to confirming the enhancement effect of the N2O bending mode on the reactivity, intricate mode specificity effects of other vibrational modes in reactants are revealed for the first time. The asymmetric stretching mode of N2O and the C–C–H bending mode of C2H2 show no effect. All remaining modes can enhance the reactivity. In particular, the vibrational excitation of the N2O symmetric stretching mode shows similar enhancement effect on the title reaction, compared to its bending mode excitation. Detailed analysis reveals that the concerted mechanism dominates with the reactants propelled sufficiently close to each other to yield product. This study advances our understanding of the chemical dynamics of the title reaction.