1. M. A. El'yashevich, Atomic and Molecular Spectroscopy [in Russian], Fizmatgiz, Moscow (1962).
2. L. M. Sverdlov, M. A. Kovner, and E. P. Krainov, The Vibrational Spectra of Polyatomic Molecules [in Russian], Nauka, Moscow (1970).
3. M. V. Vol'kenshtein, L. A. Gribov, M. A. El'yashevich, and B. I. Stepanov, The Vibrations of Molecules [in Russian], Nauka, Moscow (1972).
4. L. A. Gribov, Introduction to Molecular Spectroscopy [in Russian], Nauka, Moscow (1976).
5. V. T. Aleksanyan and B. V. Lokshin, The Structure of Molecules and the Chemical Bond [in Russian], Vol. 5, Moscow (1976), p. 11.