1. B. P. Lugovkin and B. A. Arbuzov. Zh. obshch. khimii22, 2041 (1952).
2. L. I. Bellamy, Infrared Spectra of Molecules [Russian translation] (IL, Moscow, 1957), p. 330.
3. V. M. Plets, Organic Compounds of Phosphorus [in Russian] (Moscow, 1940), p. 303.