1. H. Bernas and M. Langevin, J. Phys. 24, 1034 (1963).
2. A summary of the early work appeared in Hyperfine Structure and Nuclear Radiations, ed. by E, Matthias and D. Shirley, North-Holland Publishing Co., Amsterdam, 1968. A paper presented at this conference — I. Dezsi, Mössbauer Effect Studies on Frozen Solutions -contains much new materials and further references back to earlier work.
3. A. Nozik and M. Kaplan, J. Chem. Phys. 47, 2960 (1967).
4. A. Nozik and M. Kaplan, Another very useful paper by these authors (Phys. Rev. 159, 2, 273 (1967)
5. P. P. Craig and N. Stein, Phys. Rev. Lett. 11, 460 (1963).