1. R. BATES and A. DALGARNO (1962) in “Atomic and Molecular Processes” (ed. D. R. Bates) p. 245, Academic Press, New York.
2. A. BETHE and E. E. SALPETER (1957) “Quantum Mechanics of One- and Two-electron Atoms”, Springer, Berlin.
3. L. D. LANDAU and E. M. LIFSHITZ (1971) “Classical Theory of Fields”, p. l8l, Pergamon Press, New York.
4. M. ABRAMOWITZ and I. A. STEGUN (1964) “Handbook of Mathematical Functions”, NBS, Washington.
5. G. N. WATSON (1966) “Treatise on the Theory of Bessel Functions”, University Press, Cambridge.