Isotope Shift in Magnesium

Abstract

The previous investigations concerning the isotope shift of magnesium have been repeated and extended by means of an improved atomic beam source and a Perot-Fabry interferometer. The values of Meissner have been checked to within experimental error in most cases. In addition, several new lines have been resolved, and their isotope shifts determined. The $3^{1}P\ensuremath{-}m^{1}D$ series has been resolved from $m=3$ out as far as the member $m=11$. In this series the values of $\ensuremath{\Delta}\ensuremath{\nu}(={\ensuremath{\nu}}_{26}\ensuremath{-}{\ensuremath{\nu}}_{24})$ seem to converge to a value of about 0.068 ${\mathrm{cm}}^{\ensuremath{-}1}$ rather than the value 0.056 ${\mathrm{cm}}^{\ensuremath{-}1}$ obtained by Meissner. The isotopic shifts of the members $m=5$ and $m=6$ of the series $3^{1}P\ensuremath{-}m^{1}S$ have been measured. The results obtained are discussed in connection with the theoretical work of Vinti, who assumed the splitting to be solely a mass effect. The experimental and theoretical values of $\ensuremath{\Delta}\ensuremath{\nu}$ agree in sign, but the former are usually larger by a factor of about two. The $3^{2}D\ensuremath{-}4^{2}F$ doublet of Mg II at 4481A has been measured very carefully and the separation of the two components found to be 1.000\ifmmode\pm\else\textpm\fi{}0.002 ${\mathrm{cm}}^{\ensuremath{-}1}$.