Resonance ionization spectroscopy of fermium (Z=100)

Laser spectroscopy has been applied for the first time to measure resonant transition frequencies of fermium (Z=100). A number of 2.7×1010 atoms was electrodeposited on a Ta filament and covered with a 1 μm Ti layer. Fm atoms were evaporated from the filament at a temperature of approximately 1000 °C into an optical cell filled with a buffer gas and were subsequently photoionized in a two-photon 1+1′ process using a tunable excimer-pumped dye laser and the excimer (XeF) laser itself to produce the resonant (1) and non-resonant (1′) photon frequencies, respectively. The created photoions were identified by mass-selective detection. We observed resonant transitions of Fm at dye-laser energies of 25 099.8(2) and 25 111.8(2) cm−1. A possible classification of these levels is given on the basis of multiconfiguration Dirac–Fock calculations. We also interpreted the recorded time of ion drift through the buffer gas as a novel way to measure the mean ionic charge radius of the heavy elements.