1. Sharma, R.R.: 1981, Physical Rev. A 13, p. 517.
2. Sharma, R.R.: 1968, J. Math. Phys. 9, p. 505.
3. Jones, H.W.: 1980, Int. J. Quantum Chem. 18, p.709; 1981, 19, p. 567.
4. Viccaro, M.H. de A.: 1976, Int. J. Quantum Chem. 10, p.1075.
5. Silverstone, H.J. and Moats, P.K.: 1977, Phys. Rev. A 16, p.173