Mass spectrometric observation and reaction mechanism of gas-phase initial intermediates during TKX-50 decomposition

5,5′-bistetrazole-1,1′-diolate (TKX-50) is a novel insensitive energetic ionic salt which demonstrates considerable application potential due to its high density, high formation enthalpy, excellent stability, and environmentally benign decomposition products. This study provides crucial new insights into the initial steps of TKX-50 thermal decomposition by employing synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS). Two key pieces of evidence were uncovered: first, the early appearance of the NH 2 OH signal (10°C ahead of the main decomposition peak) offers direct experimental proof that proton transfer and hydroxylamine formation precede tetrazole ring-opening. Second, the detection of fragments with an intact tetrazole skeleton (e.g., at m/z = 68.014 and 70.027) reveals a previously overlooked competitive pathway involving direct C-C bond cleavage, which operates alongside the conventional stepwise ring-opening route. Combined with theoretical calculations, this work elucidates a complex, multi-stage decomposition network with parallel reaction channels.