1. Wong, Stafsudd, and Johnson, Journal Chem. Phys.,30, no. 3, 1963.
2. W. Low, J. Makowsky, and S. Jatsiv, Quantum Electronic Proceedings of the 3rd Congress, Paris, vol. 1, p. 655, 1964.
3. G. H. Dieke and H. M. Grosswhite, Applied Optics,2, 675, 1963.
4. R. W. Kedrie and M. Kestigiant, Applied Physics Letters,4, no. 7, 124, 1964.
5. N. A. Tolstoi and P. P. Feofilov, UFN,41, 1, 44, 1950.