Abstract
By considering the variation of charge-transfer energy and of the intensity parameters across isostructural series it is concluded that charge-transfer mixing is of negligible importance in accounting for the intensity of the hypersensitive transitions of the trivalent lanthanides. The experimental relationship between hypersensitive transition intensity and charge-transfer energy found for a particular member of the lanthanide series in various environments can be as satisfactorily explained by the ligand polarization theory as by charge-transfer mixing.