1. L. V. Keldysh, Sov. Phys. JETP 20, 1307 (1964).
2. V. S. Popov, V. P. Kuznetsov, and A. M. Perelomov, Sov. Phys. JETP 26, 222 (1967).
3. A. I. Baz’, Ya. B. Zel’dovich, and A. M. Perelomov, Scattering Reactions and Decays in Nonrelativistic Quantum Mechanics (Nauka, Moscow, 1989; Israel Program for Scientific Translation, Jerusalem, 1969).
4. V. S. Popov, B. M. Karnakov, and V. D. Mur, J. Exp. Theor. Phys. 86, 860 (1998).
5. S. V. Kryuchkov and G. A. Syrodoev, Izv. Vyssh. Uchebn. Zaved., Radiofiz., No. 6, 762 (1990).