Vibrational Signatures of Unrealized Phosphorus Suboxide Intermediates in White Phosphorus Oxidation Reactions

White phosphorus ignition notoriously produces the phosphoric acid anhydride P₄O₁₀, yet the intermediate oxidation steps remain undetermined. We report the first geometric and vibrational characterization of two P₄O₂ isomers, P₃OPO and P₃PO₂, and substantiate a previously proposed cyclic P₄O₂ isomer. We formally assign the infrared bands observed by Andrews and Mielke at 898 and 891 cm^-1 to the antisymmetric P-O-P vibrations of P₃OPO species (Mielke and Andrews, 1990). Additional bands corresponding to terminal P═O and -PO₂ stretches of P₃OPO and P₃PO₂ discussed herein also went unrecognized due to the peculiar bonding of P₄O₂ species compared to oxo-bridged P₄O_x (x = 3-6) species. Sequential addition of oxygen atoms to the P₄ tetrahedron appears to form P₃OPO and P₃PO₂, while cyclic P₄O₂ is formed from P₂O dimerization. CCSD(T) geometries, CCSD(T) + MP2[δVPT2] fundamental frequencies, and enthalpies of formation extrapolated using focal-point analysis are reported. The predicted enthalpies of formation relative to tetrahedral P₄ plus ³Σ_g^- O₂ for bent-P₃OPO, extended-P₃OPO, P₃PO₂, and cyclic-P₄O₂ are -93, -88, -85, and -63 kcal mol^-1, respectively.