Electronic-Absorption Spectra of Gaseous NiCl2, NiBr2, and NiI2. Axial Ligand Field Calculations Including Spin—Orbit Coupling

Abstract

Electronic‐absorption spectra of gaseous NiCl₂, NiBr₂, and NiI₂ have been measured in the range 4000–20 000 cm⁻¹. An interpretation of the low‐intensity dⁿ←dⁿ transitions is given based on ligand field calculations for a 3d⁸ configuration in an axial field including spin—orbit coupling. The main features of the spectra are due to transitions to ³P_π and ¹D_Δ,π excited states which are strongly intermixed in the bromide and iodide. An analysis of the nephelauxetic effect in these levels leads to the conclusion that the F₂ parameter decreases more rapidly than the F₄ parameter in the series NiCl₂–NiBr₂–NiI₂.