Anomalies in the optical isotope shifts of samarium

Abstract

Measurements of the even-even isotope shifts in seven Sm spectral lines made using tunable dye laser heterodyne spectroscopy are presented. Anomalies in the isotope shifts in the level at 19 192 cm^-1 in the Sm I spectrum reported previously have been confirmed to within experimental uncertainty by data from the line at 564.75 nm which couples to that level. Results from the line at 565.28 nm show equal and opposite deviations, from straight lines fitted through King plots, to the anomalies produced by the data from the 19 192 cm^-1 level. This has been interpreted as demonstrating that the upper level of the 565.28 nm transition, which is at 19 174 cm^-1, is mixed with that at 19 192 cm^-1. An explanation of the mixing in terms of second-order perturbations due to the isotope shift operators is presented. Other closely spaced pairs of levels do not show anomalies to within present experimental uncertainty.