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DOE OSTI · 3513123

Bond Dissociation Energy, Ionization Energy, and Electronic Structure of Thorium Dimer

Kawagoe, Thomas T. [University of Utah, Salt Lake City, UT (United States)] (ORCID:0000000298624625)·Morse, Michael D. [University of Utah, Salt Lake City, UT (United States)] (ORCID:0000000223867315)·Ariyarathna, Isuru [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000252594248)
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Abstract

Diatomic thorium, Th 2 , has been investigated using a laser ablation, supersonic expansion source to produce the molecule and resonant two-photon ionization spectroscopy to measure its bond dissociation energy (BDE) and ionization energy (IE). The molecule has a high density of states in the vicinity of its bond dissociation energy, leading to rapid predissociation as soon as this energy is exceeded. The BDE is identified from this predissociation threshold as D 0 (Th 2 ) = 2.857(7) eV, where the assigned error limit is provided in parentheses in units of the last quoted digit. Similarly, the one-photon ionization threshold has been measured, providing the ionization energy IE(Th 2 ) = 5.042(4) eV. Together with a thermochemical cycle and the atomic ionization energy, these values provide the BDE of the cation, giving D 0 (Th 2 + ) = 4.122(8) eV. Computations show that Th 2 has three nearly degenerate low-lying electronic states (1 3 Σ u + , 1 1 Σ g + , and 1 3 Δ g ) with bonding dominated by 7s and 6d orbitals, indicating predominantly transition-metal-like behavior. The 1 3 Σ u + state exhibits a triple bond, whereas the 1 1 Σ g + and 1 3 Δ g states possess quadruple-bond character and correspondingly shorter bonds. Although 1 3 Σ u + is predicted to be the lowest state without spin–orbit coupling, the large spin–orbit stabilization of the 1 3 Δ g state makes its Ω = 1 g component the ground state. Furthermore, the calculated dissociation energy (2.840 eV) and ionization energy of Th 2 (5.098 eV) are both in excellent agreement with experiment.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY74 ATOMIC AND MOLECULAR PHYSICSbond cleavagebond dissociation energychemical calculationsionizationionization energymetal dimermoleculesquantum mechanicsthermochemistrythorium

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Kawagoe, Thomas T. [University of Utah, Salt Lake City, UT (United States)] (ORCID:0000000298624625), Morse, Michael D. [University of Utah, Salt Lake City, UT (United States)] (ORCID:0000000223867315), Ariyarathna, Isuru [Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)] (ORCID:0000000252594248). 2026-08-26. Bond Dissociation Energy, Ionization Energy, and Electronic Structure of Thorium Dimer. https://doi.org/10.1021/jacs.6c13640

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