Theoretical Study of the Subsequent Decomposition Mechanisms of 1,1-Diamino-2,2-dinitroethene (FOX-7)

Abstract

This computational study focuses on the mechanism of the consecutive decomposition of FOX-7 and compares the results with recent experimental study [J. Phys. Chem. A 2023, 127, 7707] under 202 nm photolysis (592 kJ/mol). The mechanisms of forming these compounds, including cyanamide variants (HNCNH and NH₂CN), hydroxylamine (NH₂OH), nitrosamine (NH₂NO), diaminoacetylene (H₂NCCNH₂), cyanogen (NCCN), water (H₂O), ammonia (NH₃), urea ((NH₂)₂CO), hydroxyurea (NH₂C(O)NHOH), and formamide (NH₂CHO), have only been speculated on without any energetic information previously. This study employed an unsupervised potential energy profile search protocol and ab initio molecular dynamics (AIMD) simulations to identify reaction pathways leading to these compounds. The calculations reveal that although some products (e.g., HNCNH, NH₂CN, H₂NCCNH₂, and NCCN) can be formed via unimolecular decomposition, other products (e.g., NH₂OH, NH₂NO, H₂O, NH₃, (NH₂)₂CO, NH₂C(O)NHOH, and NH₂CHO) are energetically favored if they are formed via bimolecular recombination between unimolecular decomposition products or a product and a FOX-7 molecule.