Gas-phase reactivity of protonated oxazolone: chemical dynamics simulations and graph theory-based analysis reveal the importance of ion-molecule complexes

This study delves into the fragmentation mechanisms of the oxazolone form (OXA) of protonated cyclo-di-glycine using chemical dynamics simulations. In this way, we were able to capture the intricate dissociation pathways for different internal energies of the system. By transforming molecular geometries into graph representations, we systematically analyze fragmentation processes and identify key intermediates and ion-molecule complexes (IMCs) that play a crucial role in fragmentation dynamics. The study highlights the distinct isomerization landscapes of OXA, driven by IMC formation, which contrasts with the previously reported behavior of cyclic and linear forms [Perez Mellor et al., J. Chem. Phys., 2021, 155, 124103]. The resulting fragmentation channels are characterized by their distinct energetic thresholds and branching ratios and can provide a molecular explanation of what was observed experimentally. Thanks to an accurate analysis of the trajectories using our graph-theory-based tools, it was possible to point out the particular behavior of OXA fragmentation, which is different from other isomers. In particular, the important role of IMCs is shown, which has an impact in populating different isomeric structures.