Dimer formation at the earlier stage of dipole clustering in manganese-doped NaCl and KCl

The aggregation kinetics of nearest-neighbor and next-nearest-neighbor ${\mathrm{Mn}}^{2+}$-cation–vacancy dipoles in manganese-doped NaCl and KCl has been analyzed at 333 and 343 K as a function of impurity concentration. To do this, we measured a large number of dipole- decay data points at short annealing times with use of the electron-paramagnetic-resonance technique. With this technique we achieved a good knowledge of the dipole-decay curve when only a small amount of dipoles had been clustered to form aggregates into the alkali halide matrix. The analyses of the data taken at the earlier stage of aggregation, without our assuming any reaction order a priori, indicates unambiguously that this dependence is the one expected for a pure second-order kinetics equation. From this result and those reported in our previous paper showing conclusively that dimers are the complexes which are formed during the very initial stage of the clustering process, it appears that the long-existing controversy of dimer versus trimer formation may be definitively solved.