1. Gutmann, F., and Lyons, L. E., Organic Semiconductors, chap. 8 (J. Wiley and Sons, 1967).
2. Riehl, N., Trans. NY Acad. Sci., Series II, 27, 772 (1965).
3. Rosenberg, B., Nature, 193, 364 (1962).
4. Maricic, S., and Pifat, G., Abhand. Deut. Akad. Wiss. Berlin, Kl. Math. Phys. Tech., 4, 63 (1966).
5. Cardew, M. H., and Eley, D. D., Disc. Faraday Soc., 27, 115 (1959).