Infrared Absorption and Local Symmetry of WO‐ and MoO Impurity Ions in KI and CsI Crystals

Abstract

In the temperature range 120 to 800 °K and frequency range 1000 to 300 cm−1 a study has been made of the infrared absorption spectra of the impurity anions WO 42−‐and MoO 42−‐in KI and CsI single crystals. It is shown that W 42− and MOO 42− form neutral complexes W 42− · M2+ and MoO 42− · M2+ in KI lattice with cations M2+ (Ca2+, Sr2+, Ba2+) similar to the complexes SO 42− · M2+, CrO 42− · M2+ and SeO 42− · M2+ observed earlier in the f.c.c. lattices. Here a lowering of the local symmetry to C2v of the impurity tetrahedrons results in the appearance of triplets in their vibration regions v3(A2) and v4(F2). The fine structure in the infrared spectrum of MoO 42− · M2+ + KI was interpreted to be isotopic. A local symmetry of the impurity WO 42− and MoO 42− in CsI lattice was not identified unequivocally from the IR absorption spectra. The latter have doublet and quartet structure in the vibration regions v1(A1) and v3(F2), respectively, and depend on the impurity tetrahedrons and M2+ cation concentration. One, probably, should assume the interstitial formation of impurities into b.c.c. lattice of CsI which results in the existence of complex anion‐cation neutral complexes of different kinds.