Predissociation measurements of the bond dissociation energies of EuO, TmO, and YbO

Dakota M Merriles; Kimberly H Tomchak; Joshua C Ewigleben; Michael D Morse

doi:10.1063/5.0068543

Predissociation measurements of the bond dissociation energies of EuO, TmO, and YbO

J Chem Phys. 2021 Oct 14;155(14):144303. doi: 10.1063/5.0068543.

Authors

Dakota M Merriles¹, Kimberly H Tomchak¹, Joshua C Ewigleben¹, Michael D Morse¹

Affiliation

¹ Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.

PMID: 34654298
DOI: 10.1063/5.0068543

Abstract

The observation of a sharp predissociation threshold in the resonant two-photon ionization spectra of EuO, TmO, and YbO has been used to measure the bond dissociation energies of these species. The resulting values, D₀(EuO) = 4.922(3) eV, D₀(TmO) = 5.242(6) eV, and D₀(YbO) = 4.083(3) eV, are in good agreement with previous values but are much more precise. In addition, the ionization energy of TmO was measured by the observation of a threshold for one-color two-photon ionization of this species, resulting in IE(TmO) = 6.56(2) eV. The observation of a sharp predissociation threshold for EuO was initially surprising because the half-filled 4f⁷ subshell of Eu in its ground state generates fewer potential energy curves than in the other molecules we have studied by this method. The observation of a sharp predissociation threshold in YbO was even more surprising, given that the ground state of Yb is nondegenerate (4f¹⁴6s², ¹S_g) and the lowest excited state of Yb is over 2 eV higher in energy. It is suggested that these molecules possess a high density of electronic states at the energy of the ground separated atom limit because ion-pair states drop below the ground limit, providing a sufficient electronic state density to allow predissociation to set in at the thermochemical threshold.