The Underlying Chemistry to Formation of Phosphoryl Radicals from Organophosphorus Compounds - A Missing Puzzle Piece in the Flame Chemistry.

: Reactive species such as ∙PO 2 and HOPO are considered of upmost importance in flame inhibition and catalytic combustion processes of fuels. However, the underlying chemistry of their formation remains speculative due to the unavailability of suitable analytical techniques which can identify the transient species that lead to their formation. This study elucidates the reaction mechanisms of formation of phosphoryl species from dimethyl methyl phosphonate (DMMP) and dimethyl phosphoramidate (DMPR) under well-defined oxidative conditions. Photoelectron photoion coincidence techniques utilizing vacuum ultraviolet (VUV) synchrotron radiation were applied to isomer-selectively detect the elusive key intermediates and stable products. With the help of in-situ recorded spectral fingerprints different transient species, such as PO 2 and triplet O radicals, have been exclusively identified from their isomeric components, which helped piece together the formation mechanisms of phosphoryl species under various conditions. It was found that ·PO 2 requires oxidative conditions above 1070 K. The combined presence of O 2 and H 2 led to significant changes in the decomposition chemistry of both model phosphorus compounds leading to the formation of ·PO 2 . The reaction ·PO + O 2 → ·PO 2 + ·O· was identified as the key step in the formation of ·PO 2 . Interestingly, the presence of O 2 in DMPR thermolysis, suppresses formation of PN containing species.