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.