Sub-Oxides of Phosphorus

Early workers described the existence of several solid yellow or orange sub-oxides to which various empirical formulae such as PO, P2O, P4O, and so on were assigned. There is growing evidence that all the oxides (4.77) and (4.78), derived from the P4 tetrahedron, and the planar structure (4.79b) may be capable of existence. The sulphur analogues of many such structures have already been characterised (Section 4.3). 

Recent studies have confirmed the existence of low-molecular-weight species of composition P4O, P2O, PO and PO2. Photolysis of P4/O3 mixtures and infrared spectra of the products trapped in solid argon indicate the existence of P4O and several of the other structures in (4.77 through 4.79) [10-12], Some sulphur analogues have already been characterised (Section 4.3). 

Unstable molecules or radicals such as P2O, PO, PO2 and PO have been observed spectroscopically [13-15], but in some cases stable metal complexes have been obtained (8.361) [16]. 

The diatomic molecule PO, which exists in interstellar space, has an interatomic distance of 1.447 A, corresponding to a multiple bond [17]. Recent studies have characterised the species PO + and confirmed others [18,19], 

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