1. Birks, J. B., and Christophorou, L. G., Nature, 194, 442 (1962).
2. Förster, Th., and Kasper, K., Z. Elektrochem., 59, 977 (1958).
3. Stevens, B., Nature, 192, 725 (1961).
4. Coulson, C. A., Orgel, L. E., Taylor, W., and Weiss, J., J. Chem. Soc., 2961 (1955).
5. Weinreb, A., J. Chem. Phys., 36, 890 (1962).