Photodetachment Spectroscopy of Ce$^{\_}$

Tunable infrared laser photodetachment spectroscopy has been performed on Ce$^{\_ }$ using a crossed laser-ion beam apparatus. The relative photodetachment cross section for neutral production was measured over the photon energy range 0.61 eV -- 0.75 eV. The spectrum reveals a threshold near 0.65 eV, which is interpreted as the opening of Ce$^{\_}$ the (4$f$5$d^{2}$6$s^{2} \quad ^{4}H_{7/2})$ to Ce (4$f$5$d$6$s^{2} \quad ^{1}G_{4})$ ground state to ground state transition. At least five narrow peaks associated with negative ion resonances are observed over the range 0.62 -- 0.70 eV, and their energies and widths are measured. The present measurements are compared to recent theoretical [1] and experimental [2] results, which are in significant disagreement on fundamental physical quantities such as the electron affinity of Ce and the ground state configuration of Ce$^{\_}$. [1] S.M. O'Malley and D.R. Beck, Phys. Rev. A \textbf{61}, 034501 (2000); X. Cao and M. Dolg, Phys. Rev. A \textbf{69}, 042508 (2004). [2] V.T. Davis and J.S. Thompson, Phys. Rev. Lett. \textbf{88}, 073003 (2002).