Hyperfine Structure of the Spectrum of Cu I and Test of the Hyperfine Structure Formulas

The hyperfine structure (hfs) of the levels 3 d 9 4 s 2 2 D 5/2 and 2 D 3/2 was measured and compared with the usual hfs formulas for d -electrons, and a discrepancy between theory and experiment was found. This can be phenomenplogically interpreted by assuming that the values of <1/ r 3 > are different for 3 d 5/2 - and 3 d 3/2 -electrons, namely <1/ r 3 >=7.4 and 8.0 for 3 d 5/2 - and 3 d 4/2 -electrons respectively, where r is measured in unit of hydrogen atom radius.