Highly excited even Rydberg series of Lu I studied by two-step laser photoionisation spectroscopy

Abstract

The highly excited even levels of the lutetium atom are studied by two-step resonance ionisation spectroscopy. Four Rydberg series, 6s2ns 2S1/2 (n=17-76), 6s2nd 2D3/2 (n=14-105), 6s2nd 2D5/2 (n=19-87) and 6s2ng 2G9/2 (n=21-61), are measured and analysed. A very weak perturbation from an unassigned J=3/2 even valence level is observed around 6s252d 2D3/2 as a dip of ion signals induced by a decrease of radiative lifetimes in the perturbed Rydberg states. Small dips observed in nearby 6s2ns 2S1/2 and 6s2nd 2D5/2 Rydberg states are interpreted as the influence of the quadrupole hyperfine interaction of 175Lu (I=7/2).