Moessbauer emission spectroscopy studies of tunneling chemical relaxation

The method of Moessbauer Emission Spectroscopy (MES) allows to study the kinetics of chemical conversions (electron and spin relaxation) of Moessbauer emitters if the time of such conversions is comparable to the life-time of Moessbauer level. Rate constants of fast interionic electron transfer from 57Fe2+(HS-high spin state) to [Fe(III)(CN)6]3-(LS-low spin state) in the transformation of Turnbull blue (TB) into the Prussian blue (PB) were measured at 400-12 K and it was found that the rate of this process reaches the low-temperature plateau value below ca. 50 K. The observations of the rate of spin relaxation (HS→LS) for various dipyridyl and phenantroline complexes of iron performed by Mainz group at 293-4 K also have lead to the revealing of low-temperature plateau of the rate of such conversions. In such a way the MES has opened new possibilities of the studies of electron-nuclear tunneling which can be described on the base of the theory of the radiationless electron transitions