Abstract

The isotope displacement effect is discussed with relation to other spectro-isotopic effects. The results of a preliminary investigation of this effect in uranium isotopes are presented. Spectrum shifts as large as a wave number between the U²³⁵ and U²³⁸ spectra are not uncommon, the shifts usually being toward the violet for the light isotope.

These wave-length differences have been correlated to the spectroscopic energy systems of U I and U II and are found to be of two types: (1) a simple isotopic displacement arising from configurationnucleus interaction, and (2) a complex isotopic displacement arising from perturbations between close-lying levels. The magnitude of shift in U I is generally of the order 0.3 cm⁻¹, but ranges from −0.7 cm⁻¹ to 1.5 cm⁻¹ in U II. Configurations involving the s² electron group show the largest isotope shifts indicating an additive type of interaction for the s electrons and the nucleus.

© 1949 Optical Society of America

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