Charge Transfer Bands of LiX: Cu²⁺ (X: Cl, Br) and Their MCD Spectra

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The absorption and MCD spectra of Cu²⁺-doped LiCl and LiBr single crystals are studied in the region 15,000∼50,000 cm⁻¹ mainly at LNT. Two absorption bands (28,150 cm⁻¹ (B) and 36,200 cm⁻¹ (C)) and three absorption bands (19,000 cm⁻¹ (B), 22,500 cm⁻¹ (B′) and 29,500 cm⁻¹ (C)) are observed at LNT in the quenched LiCl: Cu²⁺ and LiBr: Cu²⁺ crystals, respectively, and assigned to the charge transfer transitions in the Cu²⁺-hexahalide complexes formed in the Li-halide host crystals. The observed absorption and MCD spectra are explained by taking into account the mixing of two t_1u molecular orbitals which consist of ligand halogen p_π and p_σ orbitals.