1. R. L. Sorochenko and M. A. Gordon, Radio Reñombination Lines (Fizmatlit, Moscow, 2003; Kluwer, Dordrecht, 2002).
2. R. L. Sorochenko and A. P. Tsivilev, “Detection of S56 and S57 Radio Lines in W3A Source-First Radio Recombination “Carbon Lines in Millimeter Range,” in Proc. of the Year Session of Sci. Soc. AKTs FIAN (Fiz. Inst. Lebedeva, Moscow, 1996), pp. 4–8.
3. R. L. Sorochenko and A. P. Tsivilev, “Physical Conditions in Photodissociation Regions from Observations of Carbon Radio Recombination Lines and IR Fine Structure Lines of CII and OI,” Astron. Zh. 77(7), 488–498 (2000) [Astron. Rep. 44, 426 (2000)].
4. A. P. Tsivilev, “Determination of the Primordial Helium Abundance from Radio Recombination Line Observations,” Pis’ma Astron. Zh. 35(10), 745–754 (2009) [Astron. Lett. 35, 670 (2009)].
5. N. Bohr, “Om brintsrektret,” Fisisk Tidsskraft. 12, 97–114 (1914).