Crystal Field of Some Monoclinic Rare-Earth Chlorides

The 15 crystal‐field parameters B_k^q=〈r^k〉A_k^q for monoclinic ErCl₃·6H₂O were found to be

$$\begin{array}{ccccc}{B}_2^0\text{=116,}& B_2^2\text{=158,}& {\mathrm{B̄}}_2^2\text{=−262,}& B_4^0\text{=−88,}& B_4^2\text{=−193,}\\ {\mathrm{B̄}}_4^2\text{=346,}& B_4^4\text{=332,}& {\mathrm{B̄}}_4^4\text{=158,}& B_6^0\text{=−9.8,}& B_6^2\text{=−70,}\\ {\mathrm{B̄}}_6^2\text{=141,}& B_6^4\text{=238,}& B_6^4\text{=−119,}& B_6^6\text{=238,}& {\mathrm{B̄}}_6^6\text{=−11.}\end{array}$$

When used together with Wybourne's free‐ion wavefunctions, the field adequately explains most of the observed Stark and Zeeman splittings. The B_k^q, modified by the calculated 〈r^k〉 of Freeman and Watson, are appropriate for several ions and, in all, account for about 200 independent data. A possible systematic variation of the A_k^q for odd and even electron ions is pointed out. The Zeeman splittings of the ${}^6{P}_{\frac{7}{2}}$ and ${}^6{P}_{\frac{5}{2}}$ states of GdCl₃·6H₂O are explained, and the use of the Gd³⁺ ion as a crystal‐field probe is discussed.