Raman spectra of deuterated potassium dihydrogen phosphate crystals with different degrees of deuteration

The polarized Raman spectra of deuterated potassium dihydrogen phosphate crystals with different deuterium concentrations are measured. With the increasing deuterium concentration, the Raman peaks which are assigned as the internal vibrations of the (H/D)₂PO^-₄ anion shift to lower wavenumbers. This red-shift contributes to the decrease in the bonding force of the P - O bond as a result of the substitution of deuterium for hydrogen. Moreover, the intensity of the strongest peak of these crystals decreases first, and reaches the minimum value while the mole percentage of the deuterium content in the crystal is about 74%. After that, the intensity increases with the increase of the deuterium concentration in the crystal.