Direct mass spectrometric observation and reaction mechanism of gas-phase initial intermediates during CL-20 decomposition

The formation and decay of initial intermediates of energetic materials (EMs) such as polynitropolyaza-caged CL-20 are responsible for the initiation of decomposition reaction network, which acts as a key mechanistic step during combustion and detonation. However, direct in situ measurements of these species have not been reported previously, and their formation mechanism remains unclear. Herein, we present direct probing of gas phase decomposition intermediates, particularly reactive initial products with parent molecule's caged skeletons from CL-20, by using in situ atmospheric pressure photoionization high-resolution mass spectrometry. The detected intermediates mainly include NO2-elimination products (C6H5O10N11, C6H6O8N10, etc.), O-elimination product (C6H6O11N12), and NO-elimination products (C6H6O11N11, etc.). Bimolecular reaction pathways involving initial intermediate C6H6O10N11 and NO2/NO are proposed and evaluated to account for the formation of initial products.