Two photon resonant excitation of Copper–Rydberg levels

The 2-photon resonant, 3-photon ionization spectrum of gaseous atomic copper is presented. The D5/223d10nd←S1/223d104s (n=9–21n=9–21) Rydberg series is observed in 2-photon excitation. The term energies of this series converge to the lowest ionization threshold with an apparent quantum defect of 0.92. The state which couples the ground S1/223d104s state of copper to the D5/223d10nd Rydberg series is a non-stationary state composed primarily of the spin–orbit components of the lowest Po2 atomic states.