The spectrum of Tm III in CaF 2

Abstract

The crystal field of CaF 2 is evaluated on a point-charge model, and from comparison with the crystal field constants derived from the optical spectrum (Kiss 1962) of Tm III in CaF 2 , empirical values of < r 4 >= 4.3 a.u., < r 6 > = 36 a.u. are found. These are considerably larger than the estimates of Freeman & Watson (1962). The crystal field data reveal a small discrepancy with the paramagnetic resonance data of Hayes & Twidell (1961), which can be resolved by the introduction of an orbital k -factor which is slightly less than unity (1 — k — 0009 ± 0-001). Comparison with the spectrum of Tm I measured by atomic beams (Ritter 1962) shows that the magnetic hyperfine constant for a free Tm III ion is (2.2 ± 0.5 )% greater, while the spin-orbit coupling is 1.2% greater, assuming a core polarization correction of the same magnitude as that measured for Eu III in CaF 2 . Similar effects are shown to occur for Ho III in CaF 2 . The results suggest that the values of < r -3 > and the spin-orbit coupling parameter ζ are only about 1 to 2 % greater for the free divalent 4 f ions than for the atoms.