Improved Cu ii Standard Wavelengths in the Vacuum Ultraviolet*

Abstract

Interferometric wavelength measurements of sixty-one copper spark lines in the region 2884 A to 1979 A have been carried out by means of a Fabry-Perot interferometer equipped with 4, 12, and 20 mm spacers. The light source used was a water-cooled hollow cathode Schüler tube operated principally with circulating helium but occasionally with circulating neon.The measurements were employed to establish the 4s and 5s even levels and 4p odd levels of Cu ii. After fixing these low levels, their values were combined with the grating measurements of Carter and Shenstone to establish the values of certain higher odd and even levels. Use was then made of the Ritz combination principle to calculate precise wavelength values of approximately sixty copper lines in the region between 1663 A and 984 A with estimated accuracies which varied from ±0.0003 A to ±0.001 A.