A combined theoretical and experimental study of photo-induced intramolecular hydrogen transfer of 2,4,6-trinitrotoluene

Abstract

Photo-induced decay may serve as a way to decompose energetic materials under some special conditions, and understanding the related mechanism is crucial to guide the determination of storage, transport and use conditions. In this work, we confirm the photo-induced intramolecular hydrogen transfer (HT) of 2,4,6-trinitrotoluene (TNT) by matrix-isolation infrared spectroscopy method; meanwhile, no backing of the H transferred isomer to the original TNT molecule is found when annealed and it exhibits an irreversible HT. With time-dependent density functional theory and state-averaged complete-active-space self-consistent-field calculations, we propose a photoisomerization path that occurs in the T₁ state. This is because the H transferred isomer can readily back to the ground state (S₀ state) by means of intersystem crossing (T₁/S₀), with a rather high energy barrier required to overcome for the reverse reaction to the original TNT molecule. Thereby, the irreversible HT when annealed is understandable.