Abstract：Based on the space group theory, the normal vibration modes of DKDP crystal were analyzed and the assigned. Raman spectra were measured at the room temperature. Results show that the lattice vibration spectra of DKDP arise mainly from the internal vibrations of D2PO-4 anionic cluster. Compared with the Raman spectra of an aqueous solution of KH2PO4 and an NaD2(PO4)2 crystal, the four internal vibration models of the D2PO-4 in DKDP were assigned as 881 cm-1(ν1)，357 cm-1(ν2)，514/541 cm-1(ν3)，965 cm-1(ν4), respectively.
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