An experimental investigation of the atomic europium anion

Abstract

The electron affinity (EA) of europium has been measured using laser photodetachment electron spectroscopy. The EA of Eu( 8 S 7/2 ) was determined to be 1.053 ± 0.025 eV. The data also show that Eu − has at least one bound excited state with binding energy of 0.864 ± 0.024 eV relative to the ground state of the europium atom. The experimental results are consistent with recent EA measurements of lanthanide atoms whose anions are predicted to have [Xe](4f n 6p) (where n is odd) configurations.

In situ formation and characterisation of singly ionised atomic europium in rare gas matrices—Luminescence spectroscopy and MP2 calculations

“…A clue to the possible identity of the species acting as the electron acceptor comes from the recent study of 39 but identification of the anion with absorption spectroscopy, was not achieved in the present UV-Vis study.…”

“…In this study, the anions were isolated in neon matrices near 4 K. 41 Our results reveal a unique case where the guest atom can possibly act both as electron acceptor and donor. Based on these observations, we expect other metal atoms with large electron affinities and strong s → 6p transitions such as Tm and Ce systems 39 will exhibit similar facile ionisation as Eu in the solid rare gases. The Eu + /RG system also offers the opportunity to study relativistic effects in heavy metal ions and strong spin-orbit coupling between p-orbitals of different spatial symmetries in one system.…”

Direct experimental observation of weakly-bound character of the attached electron in europium anion

“…This situation is especially true for most of the lanthanide anions except La − and Ce − since the yields of the latter were found three orders of magnitude greater than those of other lanthanide anions14. In early 2000s, a series of measurements of EAs of lanthanides were attempted by Davis and Thompson, including Eu15, Tm16, and Pr17. EAs of ~1 eV were reported for these lanthanides, implying a relatively strong interaction between the extra electron and the neutral.…”

Autodetachment lifetime calculations of long-lived metastable states of Ba−and Eu−

“…Tm − [1], Ce − [2], and Eu − [3]. In some cases these values are ∼0.5 to ∼0.9 eV higher than earlier calculated electron affinities [4,5].…”

“…While it is unlikely that a single explanation may be found to resolve the differences between experiment and theory in all these cases, our efforts have been directed toward studies of long lived excited states, most recently in Tm − [6]. The supposition is that the experiments [1,2,3] may be measuring the difference between a metastable state of the negative ion and an excited threshold of the neutral atom rather than the true electron affinity (EA).…”