The Difference between Series Spectra of Isotopes


PROF. P. ZEEMAN mentioned to me recently some new measurements of the absorption spectrum of lithium which he undertook in order to prove the presence of both isotopes. It seems to me, that at the present time it is not certain what one should expect here theoretically. Bohr's formula for the change in the frequency v due to the motion of the nucleus has been applied by him only to the cases in which a single electron moves around the nucleus; namely, to H and He+. Recently the formula has been also applied by various authors (see F. W. Aston, "Isotopes," p. 123—London 1922) to the calculation of the difference between series spectra of isotopes; this means to atoms in which several electrons move around the nucleus. So far as I know there are as yet no investigations on the equation which must for these cases replace Bohr's equation (M1, M2, m are respectively the masses of the nucleii of the isotopes and of the electron; v1, v2 are the frequencies of corresponding lines).

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EHRENFEST, P. The Difference between Series Spectra of Isotopes. Nature 109, 745 (1922).

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