P. R. Bunker (1964). „The Rotation-Torsion Wavefunctions of Molecules that have two Identical Rotors”. Mol. Phys. 8: 81. doi:10.1080/00268976400100091.
Oldani, M.; et al. (1985). „Pure rotational spectra of methane and methane-d4 in the vibrational ground state observed by microwave Fourier transform spectroscopy”. Journal of Molecular Spectroscopy. 110 (1): 93—105. Bibcode:1985JMoSp.110...93O. doi:10.1016/0022-2852(85)90215-2.
Oldani, M.; et al. (1985). „Pure rotational spectra of methane and methane-d4 in the vibrational ground state observed by microwave Fourier transform spectroscopy”. Journal of Molecular Spectroscopy. 110 (1): 93—105. Bibcode:1985JMoSp.110...93O. doi:10.1016/0022-2852(85)90215-2.