Hyperfine Structure of Thallium II

Abstract

WE have recently published two communications¹ concerning an isotope displacement effect in the hyperflne structure of thallium II. On the other hand, in a recent paper on this subject,² J. C. McLennan and M. F. Crawford state that they have discovered no trace of an isotope effect. In order to avoid misunderstanding, we wish to point out that this apparent contradiction is entirely due to the fact that the resolving power of the grating used by McLennan and Crawford is insufficient to separate the lines due to the two isotopes. The smallest separation resolved by McLennan is Δv = 0.370 cm.^-1; the largest isotope displacement is Δv = 0.280 cm.^-1. With a Fabry-Perot étalon we were able to resolve separations of Δv = 0.040 cm.^-1, that is, a tenth of the resolution obtained by McLennan.