Raman-Spectroscopic Measurements of the First Dissociation Constant of Aqueous Phosphoric Acid Solution from 5 to 301 °C

摘要

Dilute aqueous phosphoric acid solutions have been studied by Raman spectroscopy at room temperature and over a broad temperature range from 5 to 301 °C. R-normalized spectra (Bose–Einstein correction) have been constructed and used for quantitative analysis. The vibrational modes of H3PO4(aq) (pseudo C3v symmetry) have been assigned. The band with the highest intensity, the symmetric stretch ν s{P(OH)3}(ν 1(a 1)) is strongly polarized while ν 4(e), the antisymmetric stretch ν asP(OH)3) is depolarized. The stretching mode of the phosphoryl group (–P=O), ν 2(a1) occurs at 1178 cm−1 and is polarized. In the range between 300 and 600 cm−1, the deformation modes are observed. The deformation mode, δ{PO–H}, involving the O–H group has been detected at 1250 cm−1 as a very weak and broad mode.