Time and temperature dependence of aftereffects in [57Co(phen)3] (ClO4)2⋅2H2O from time-differential Mössbauer emission spectroscopy

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Abstract
Using the time‐differential Mössbauer coincidence technique we have measured emission spectra of [57Co(phen)3] (ClO4)2⋅2H2O (phen=1, 10‐phenanthroline) in the temperature range 10–80 K versus K4[Fe(CN)6]⋅3H2O as absorber. The lifetimes of the unstable 57Fe(II) high‐spin states (5T2), which are formed as a consequence of the EC process of 57Co in the source matrix, have been derived. Including the results from earlier time‐integral Mössbauer emission studies on the same system we find lifetimes ranging from 23 ns at 223 K to 393 ns at 10 K. The temperature dependence of the lifetime τ (5T2) is discussed assuming two possible decay mechanisms: (a) the tunneling of an electron to recombine with a ligand radical formed by autoradiolysis, and (b) the radiationless transition of an electronically excited spin state.