Structure of theD2Terms of the Arc Spectrum of Lithium

Abstract

Interferometric wave-length measurements of high precision carried out by employing an atomic beam light source have been used for the study of several features of the arc spectrum of ${\mathrm{Li}}^7$. Due to the great sharpness of the spectral lines produced by this source it was possible to determine the splitting of several ${}_{}{}^2{}_{}{}^{}D$ terms. The hyperfine structure of the line 6708A was found in approximate agreement with earlier investigations. Precise wave-length measurements have been carried out relative to krypton standards. Discrepancies between the wave-lengths of this investigation and those of earlier investigators must be ascribed to lack of resolution or inadequate comparison methods employed in earlier investigations. This consideration is substantiated by our measurements carried out with a vacuum lithium arc, the results of which are consistent with the atomic beam values. Isotopic shift (${\mathrm{Li}}^6$ and ${\mathrm{Li}}^7$) of the resonance line 6708A was measured.