Abstract
New wavelength measurements in the vacuum ultraviolet (VUV), ultraviolet and visible spectral regions have been combined with available literature data to refine and extend the description of the spectrum of singly ionized copper (Cu II). In the VUV region, we measured 401 lines using a concave grating spectrograph and photographic plates. In the UV and visible regions, we measured 276 lines using a Fourier-transform spectrometer. These new measurements were combined with previously unpublished data from the thesis of Ross, with accurate VUV grating measurements of Kaufman and Ward, and with less accurate older measurements of Shenstone to construct a comprehensive list of ≈2440 observed lines, from which we derived a revised set of 379 optimized energy levels, complemented with 89 additional levels obtained using series formulas. Among the 379 experimental levels, 29 are new. Intensities of all lines observed in different experiments have been reduced to the same uniform scale by using newly calculated transition probabilities (A-values). We combined our calculations with published measured and calculated A-values to provide a set of 555 critically evaluated transition probabilities with estimated uncertainties, 162 of which are less than 20%.
Highlights
The spectrum of singly ionized copper, belonging to the Ni isoelectronic sequence, has a long history of research
We found the leading terms to be 49% of 3d8(1G)4s4p(3P◦) 3P◦ 5D◦ sp (3P)◦ 5F◦ sp (3F)◦, 39% of 3d96p 3F◦, and only 5% of the term given as label by Sugar and Musgrove
Transition probabilities of Cu II were reported in 42 papers, the full list of which can be found in the National Institute of Standards and Technology (NIST) Atomic Probability Bibliographic Database (Kramida and Fuhr [59])
Summary
The spectrum of singly ionized copper, belonging to the Ni isoelectronic sequence, has a long history of research. Nave and Sansonetti [20] showed that Ritz wavelengths below 2400 Å (41667 cm−1) derived from Ross’s Cu II energy levels are systematically too low, the mean relative deviation being about 4 × 10−7. This error is significantly greater than the average relative uncertainty of Ritz wavenumbers given by Ross, 1.2 × 10−7. The energy levels and Ritz wavelengths derived from these measurements do not pertain to a real atom, but rather are empirical values that best describe the spectrum as normally observed
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