1. V. V. Gruzinskii and T. G. Staneva, in: Reports to the Sixth National Conference on Spectroscopy with International Participation [in Bulgarian], Bulgaria (1974), p. 117.
2. L. G. Pikulik, L. F. Gladchenko, and A. D. Das'ko, in: Quantum Electrons and Laser Spectroscopy [in Russian], Minsk (1971), p. 120.
3. N. A. Borisevich, V. V. Gruzinskii, I. I. Kalosha, and V. A. Tolkachev, Zh. Prikl. Spektrosk.,11, 173 (1969).
4. T. G. Staneva, Zh. Prikl. Spektrosk.,20, 199 (1974).
5. V. I. Studenov and N. G. Bakhshiev, Opt. Spektrosk.,36, 392 (1974).