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

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.