AbstractTrapped electrons,ec−, are produced by photoionization of K4Fc(CN)6in 10MNaOH/H2O and 10MNaOD/D2O glasses at 4.2°K. The linewidth,ΔHms, ofec−changes reversibly between these two temperatures in contrast to the observations for organic matrics. Three proposed mechanisms including dipole relaxation of pendent molecules surrounding the electron cavity, contraction‐expansion model of cavity, and electron retrapping process are each discussed. It appears that no one physical model satisfactorily accounts for the present observations. The electron retrapping process, however, might be a better condidate for interpreting the experimental results in compatible with the optical absorpti