1. Lord RayleighTheory of Sound, 1948, pp. 76–78.
2. Herzberg, G.Spectra of Diatomic Molecules, Second Edition, pp. 90–102.
3. Fermi, E.Moleküle und Kristalle, p. 140.
4. Magnus, W. and OberhettingerFormulas and Theorems for the Special Functions of Mathematical Physics, 1949, 108.
5. Whittaker and WatsonModern Analysis, Fourth Edition (Chapters XXI and XXII).