The Mössbauer spectra of ferric hemin are interpreted on the basis of a temperature-dependent electronic spin-spin relaxation time. The relaxation slows down with increasing temperature as a result of a change in population of ionic energy levels. The slowing down of the relaxation time, together with other effects resulting from population changes, produces a quadrupole-split line which becomes asymmetric as the temperature is increased.

• Received 27 January 1967

DOI:https://doi.org/10.1103/PhysRevLett.18.305