Optical Spectra of Divalent Manganese Salts. II. The Effect of Interionic Coupling on Absorption Strength

The visible absorption spectrum of Mn++ salts consists of spin-forbidden transitions. It is found that the intensity of these transitions in different salts depends on the interionic coupling, being too great for vibronic effects and lacking the temperature dependence expected for a vibronic mechanism. The discovery of magnon sidebands in several Mn++ salts provides detailed insight as to the nature of this coupling. It is proposed that the spin-forbidden transitions in salts (not only Mn++ salts), in which the metal ions are bridged by a single anion, occur by way of a simultaneous electronic transition in one ion and a spin deviation in the neighbor.