Two-color resonance ionization mass spectrometry of hafnium

We have observed high-lying Rydberg series converging to the first ionization limit of Hf atoms (5d6s(2) D-2(3/2)) by two-color resonance ionization spectroscopy. The observed series were excited through three different intermediate states, 5d(2)6s6p D-5(1), F-3(2), F-3(3). This suggests the correlation between s and d electrons is important. Using the quantum defect theory, the converging limit of one of the observed series was in good agreement with the established value.