The Triplet Hydroxyl Radical Complex of Phosphorus Monoxide.

Phosphorus monoxide ( PO) is a key intermediate in phosphorus chemistry, and its association with the hydroxyl radical ( OH) to yield metaphosphorous acid (cis-HOPO) contributes to the chemiluminescence in the combustion of phosphines. When photolyzing cis-HOPO in an Ar-matrix at 2.8 K, the simplest dioxophosphorane HPO and an elusive hydroxyl radical complex (HRC) of PO form. This prototypical radical-radical complex reforms into cis-HOPO at above 12.0 K by overcoming a barrier of 0.28±0.02 kcal mol . The vibrational spectra of this HRC and its D- and O-isotopologues suggest a structure of OH⋅⋅⋅OP , for which a triplet spin multiplicity with a binding energy of -3.20 kcal mol has been computed at the UCCSD(T)-F12a/aug-cc-pVTZ level.