Exchange interactions in a trigonal chromium(III) pair

Abstract

The singly excited ² E pair states in Cs₃Cr₂Br₉ exhibit fine structure which has been analysed by absorption, MCD and transverse Zeeman spectroscopy and the theory given in part I (reference [1]). The corresponding transitions in Cs₃Cr₂Cl₉ overlap with the ⁴ T ₂ band and are weak and broad. Both singleion and exchange-induced transition electric dipoles are important in the pair transitions. There is evidence for the breakdown of the Landé interval rule for the exchange-split excited pair levels. The non-vanishing intensity observed in one ΔS = 2 pair transition requires the inclusion of anisotropic exchange terms in the pair hamiltonian. MCD and Zeeman spectroscopy give, in many cases, a precise identification of the spinor pair states.