Measurements of atomic quadrupole coupling constants

Urf being the selected radio frequency and H the homogeneous field applied. This original setup was then widely used for the determination of the magnetic and quadrupolar hyperfine structure (hfs) constants A and B. Hereby one has to consider that the additional magnetic field further splits the atomic energy levels now characterized by F into (2F + 1) sublevels and mixes states of the same Mp but different F values. A Zeeman term has therefore to be added to the hyperfine Hamiltonian according to 

In those days electric field gradients could not be evaluated to a high degree of accuracy and correction factors for relativistic effects and polarization of the atomic core (Sternheimer shielding) had to be applied transferring this inaccuracy to the final NQM values. 

In order to obtain conclusive results one normally focuses on a single transition and detects the emitted fluorescence photons bearing the fine structure information. This is achievable by dye lasers or tunable laser diodes. In some setups the light travels collinearly to fast atomic beams which has some advantages with respect to spectral resolution [44]. The technique of fast ion beam spectroscopy has been applied to numerous measurements on rare earth ions, e.g. [45-49]). Some more recent high-resolution optical hfs measurements include Ta [50], [51] and the noble gas Xe [52] illustrate these advanced 

An interesting modification of optical excitation especially for the accurate determination of isotope shifts is a combination of resonance excitation / ionisation and a mass spectrometric analysis of the ions created as it is realized in RIMS (resonance ionization mass spectrom- 

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