Abstract

The reflecting echelon interferometer has been used to determine isotope shift in eleven wavelengths in the zinc arc spectrum between λ2000 A and λ5000 A. Small quantities of enriched Zn 64, Zn 66, and Zn 68 isotopes were excited in Schüler type discharge tubes with liquid nitrogen cooling. In this way isotope shifts well below the resolving limit of the echelon have been investigated. The normal mass and volume effects have been calculated and subtracted from the observed isotope shift, the difference being attributed to the specific mass effect. For the resonance lines λ2139 A (4s^{2 1}S₀–4s4p ¹P₁) and λ3076 A (4s^{2 1}S₀–4s4p ³P₁) the specific mass effect is larger than the normal mass effect and is in the same direction. The results confirm the work of Crawford, Gray, Kelly, and Schawlow. For the other wavelengths investigated, the specific mass effect is slightly smaller than the normal mass shift and is in the opposite direction.

© 1958 Optical Society of America

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