Spectroscopic manifestation for the isotopic substitution in potassium dihydrogen phosphate

The normal vibration spectra of potassium dihydrogen phosphate (KDP) and its deuterated analogue K(DxH1−x)PO4 (DKDP), which arise mainly from internal vibrations of PO4 tetrahedrons, were recorded by the micro-Raman spectrophotometer system. The four characteristic internal vibration modes of the (H/D)2PO4 anion in (D)KDP are assigned by comparing their polarized Raman spectra. The bands of H-vibrations recorded in the FTIR spectra, which have been interpreted as the O–H/D stretching modes, the in-plane bending, and the out-of-plane bending vibrations, are tentatively assigned as well. The frequency ratio of the O–H/D modes due to the hydrogen or deuterium is 1/1.37, which coincides with the ratio of square root of the reduced mass of O–H and O–D.