1. V. P. Silin, Zh. Éksp. Teor. Fiz. 47, 2254 (1964) [Sov. Phys. JETP 20, 1510 (1964)].
2. A. E. Kazakov, M. V. Fedorov, and F. V. Bunkin, Usp. Fiz. Nauk 107, 559 (1973) [Sov. Phys. Usp. 15, 416 (1973)].
3. G. J. Pert, J. Phys. B 29, 1135 (1996).
4. V. P. Krainov, J. Phys. B 33, 1585 (2000).
5. V. P. Krainov, Zh. Éksp. Teor. Fiz. 119, 1109 (2001) [JETP 92, 960 (2001)].