1. C.A. Hutchison, Jr. and B.W. Nagnum, J. Chem. Phys.
34, 908 (1961).
2. J. Brossel and A. Kastler, Compt. Rend.
229, 1213 (1949).
3. J. Brossel and F. Bitter, Phys. Rev.
86, 308 (1952).
4. G.W. Series, Repts. Progr. Phys.
22, 280 (1959)
5. B. Budick, in Advances in Atomic and Molecular Physics, Academic Press, New York (1967).