Electronic Structure ofFCenters: Hyperfine Interactions in Electron Spin Resonance

It is shown that the observed width of the microwave electron spin resonance absorption lines associated with F centers in KCl, NaCl, and KBr crystals can be attributed to hyperfine interactions between the F-center electron and the nuclear magnetic moments of the ions adjacent to the F center. The width arises from the distribution of nuclear moment components. Theoretical calculations of the width are in good agreement with observation provided that the F-center wave function is treated as a linear combination of atomic orbitals; wave functions calculated on continuum models are shown to be unsatisfactory. The theory is confirmed by a comparison of observations on F centers in crystals of K³⁹Cl and K⁴¹Cl. If the width is attributed to interactions with the nearest sets of K and Cl ions, the experiments lead directly to quantitative values of the electronic charge density at the K and Cl nuclei: one finds |Ψ(K)|²=0.70×10²⁴ cm^-3 and |Ψ(Cl)|²=0.12×10²⁴ cm^-3.