On the electronically nonadiabatic decomposition dynamics of furazan and triazole energetic molecules

The combined results of ab initio electronic-structure calculations, nonadiabatic molecular dynamics simulations using ab initio multiple spawning, and previous spectroscopic investigations of jet-cooled molecules provide strong evidence of a (π,σ^*)-mediated decomposition mechanism for the furazan and triazole energetic molecules. The importance of dissociative excited states formed by electron promotion from a π molecular orbital to a σ^* molecular orbital is explored for the furazan and triazole energetic molecules. Dissociative (π,σ^*) states of furazan and triazole energetic molecules can be populated by nonadiabatic surface jump from the (π,π^*) or the (n,π^*) state. Finally, conical intersections between (π,σ^*) potential energy surfaces (PESs) and the ground PES influence the eventual fragmentation dynamics of the furazan and triazole energetic molecules. Due to structural similarity of the triazole molecule with the pyrrole molecule, a comparison of nonadiabatic dynamics of these two molecules is also presented. The N-N bond dissociation is found to be a barrierless pathway for the triazole molecule, whereas the N-H bond dissociation exhibits a barrierless pathway for the pyrrole molecule. The present work, thus, provides insights into the excited-state chemistry of furazan and triazole energetic functional groups. The same insight can also be relevant for other energetic molecules.