Measurement of the electron affinities of the lanthanides

Laser photodetachment electron spectroscopy experiments have been performed at the Negative Ion Research Facility at the University of Nevada, Reno, to determine the electron affinity of several of the lanthanides. Electron affinities are reported for some lanthanides, while limits on the electron affinities for others are inferred from experimental results. In particular, electron affinities are reported for Ce (0.995 eV), Lu (0.346 eV), Pr (0.962 eV), Tm (1.029 eV), and Eu (1:053 eV). The electron affinities of Nd and Tb are estimated to be above 1.916 eV and 1.165 eV respectively. The electron affinity of Dy is estimated to be positive, while the electron affinity of Yb is estimated to be negative. The experimental evidence presented here is found to be in agreement with theoretical studies that predict the formation of lanthanide negative ions via the attachment of a 6p electron. Brief summaries of theories of many-electron atoms are presented, as well as the basic theory of negative ion formation and photon-ion interactions. Also presented is a discussion of basic current theoretical techniques used to determine the electron affinity and the electronic structure of negative ions. In particular, the Hartree-Fock and Dirac-Hartree-Fock central field approximations, relativistic density functional theories, and several multiconfigurational techniques are reviewed. A brief discussion of some current theoretical research employing these techniques is also included. Details of the experimental apparatus used in this study as well as the process for creating the negative ion beams are offered. The experimental results of this study are summarized and compared to current theoretical calculations for the electron affinities and electronic structures of the lanthanide atomic anions. There is strong disagreement between the results of this study and the predictions of central field theory calculations and density functional theory calculations. It is found that the relativistic coupled cluster method (a multconfigurational approximation technique) is the method that provides the best agreement with the results of this study. Finally, suggestions for future research avenues are offered.