Spectra of phosphorus compounds—I the infra-red spectra of orthophosphates

Abstract

Infra-red spectra of PO³⁻₄, HPO²⁻₄, H₂PO⁻₄ ions, phosphoric acid, and their deuterated analogues, in aqueous solution and in a number of crystalline salts, are reported. The spectra, together with published Raman data, are assigned on the basis of changes in symmetry through the series PO³⁻₄ (T_d), HPO²⁻₄ (pseudo—C_3v), H₂PO⁻₄ (C_2v, or lower), H₃PO₄ (lower than pseudo-C_3v). The origin of subsidiary or double OH stretching bands is discussed. Bands in the region of 2300–2400 cm⁻¹ (1750–1850 in deuterated compounds) are attributed to proton-tunnelling effects; bands in the 1600–1850 cm⁻¹ region probably arise from combination tones. The POH in-plane deformation mode absorbs in the region of 1250 cm⁻¹.