On the Radiofrequency Spectra of Sodium, Rubidium and Caesium

The hyperfine structures of the ground state of Na²³, Rb⁸⁵, Rb⁸⁷ and Cs¹³³ were measured by observing radiofrequency spectra of these atoms. In each case the particular lines chosen for study and the magnetic fields at which they were observed were such as to yield the greatest precision for the hyperfine structure measurements, consistent with frequencies conveniently obtainable in our laboratory (up to 700 megacycles). The measured h.f.s. separations are given both in absolute frequency units and in wave numbers.