The Simplest Phosphinylperoxy Radical and Its Isomers in the Photochemical Phosphorus‐Hydrogen‐Oxygen Network

The oxidation of phosphine (PH₃) plays an important role in the photochemical phosphorus-hydrogen-oxygen network of the Earth's atmosphere. The phosphinyl radical (•PH₂) is a key intermediate in the photochemistry of PH₃, and its reactions with O₂ yield phosphorus oxyacids as stable reservoirs via the intermediacy of yet elusive radicals. Herein, we report the identification of the simplest phosphinylperoxy radical H₂POO• in gas phase reaction between •PH₂ and O₂. The characterization of H₂POO• with matrix-isolation IR and UV-vis spectroscopy is supported by D- and ¹⁸O-isotope labeling experiments and quantum chemical calculations. Upon photoexcitation at 410 nm, the matrix-isolated H₂POO• undergoes successive hydrogen-migration to form two isomers HP(O)OH• and •P(OH)₂. Further UV-irradiation at 365 nm causes decomposition to yield the water complex of phosphorus monoxide (•PO), which can be photolytically converted to metaphosphorous acid (HOPO). The disclosed photochemistry of these novel phosphorus-bearing molecules helps in understanding the photochemical network of PH₃ in the atmospheric and interstellar phosphorus chemistry.