Phosphorescence of Tetrahalomanganate Ions in Fused Salts

The phosphorescence of tetrabutylammonium tetrachloro-, tetrabromo-, and tetraiodomanganates was examined in the molten state. Absorption and emission spectra and phosphorescence lifetimes were obtained as functions of the temperature. For the tetrachloro- and tetrabromomanganates, the rates of radiationless transfer to the ground state, as evidenced by the falling off of the phosphorescence lifetimes, begin to be noticed in the solid state, increase abruptly at the melting points, and continue to increase slowly in the liquid state. For the tetraiodomanganate, no change in phosphorescence lifetime is seen on passing through the melting point. Self-quenching is absent for all three. The offsets in the absorption and phosphorescence spectra indicate that there is a considerable change in internuclear distance on passage to the excited state, which may be expected to display Jahn-Teller distortion. The form of the temperature dependence and symmetry considerations appear to rule out a vibronic mechanism for the radiationless process. It is proposed that a spin-rotation interaction mixes the ground and excited states and thus brings about the radiationless transfer.