Probing Chemical Bonding and Electronic Structures in ThO- by Anion Photoelectron Imaging and Theoretical Calculations

Because of renewed research on thorium-based molten salt reactors, there is growing demand and interest in enhancing the knowledge of thorium chemistry both experimentally and theoretically. Compared with uranium, thorium has few chemical studies reported up to the present. Here we report the vibrationally resolved photoelectron imaging of the thorium monoxide anion. The electron affinity of ThO is first reported to be 0.707 +/- 0.020 eV. Vibrational frequencies of the ThO molecule and its anion are determined from Franck Condon simulation. Spectroscopic evidence is obtained for the two-electron transition in ThO-, indicating the strong electron correlation among the (7s sigma)(2)(6d delta)(1) electrons in ThO- and the (7s sigma)(2) electrons in ThO. These findings are explained by using quantum-chemical calculations including spin orbit coupling, and the chemical bonding of gaseous ThO molecules is analyzed. The present work will enrich our understanding of bonding capacities with the 6d valence shell

Candidate for Laser Cooling of a Negative Ion : High-Resolution Photoelectron Imaging of Th

Laser cooling is a well-established technique for the creation of ensembles of ultracold neutral atoms or positive ions. This ability has opened many exciting new research fields over the past 40 years. However, no negatively charged ions have been directly laser cooled because a cycling transition is very rare in atomic anions. Efforts of more than a decade currently have La- as the most promising candidate. We report on experimental and theoretical studies supporting Th- as a new promising candidate for laser cooling. The measured and calculated electron affinities of Th are, respectively, 4901.35(48) cm-1 and 4832 cm-1, or 0.607 690(60) and 0.599 eV, almost a factor of 2 larger than the previous theoretical value of 0.368 eV. The ground state of Th- is determined to be 6d37s2 F43/2e rather than 6d27s27p G45/2o. The consequence of this is that there are several strong electric dipole transitions between the bound levels arising from configurations 6d37s2 and 6d27s27p in Th-. The potential laser-cooling transition is S1/2o2↔F43/2e with a wavelength of 2.6 μm. The zero nuclear spin and hence lack of hyperfine structure in Th- reduces the potential complications in laser cooling as encountered in La-, making Th- a new and exciting candidate for laser cooling

Observation of electric-dipole transitions in the laser-cooling candidate Th- And its application for cooling antiprotons

Despite the fact that the laser-cooling method is a well-established technique to obtain ultracold neutral atoms and atomic cations, it has rarely if ever been applied to atomic anions due to the lack of suitable electric-dipole transitions. Efforts of more than a decade have until recently only resulted in La- as a promising anion candidate for laser cooling, but our previous work [Tang et al., Phys. Rev. Lett. 123, 203002 (2019)10.1103/PhysRevLett.123.203002] showed that Th- is also a potential candidate. Here we report on a combination of experimental and theoretical studies to determine the frequencies and rates, as well as branching ratios, for the relevant transitions in Th-. The resonant frequency of the laser-cooling transition is determined to be ν=123.455(30) THz [λ=2428.4(6)nm]. The transition rate is calculated as A=1.17×104s-1. Since the branching fraction to dark states is negligible, 1.47×10-10, this represents an ideal closed cycle in Th- for laser cooling. Furthermore, the zero nuclear spin of Th232 makes the cooling process possible in a Penning trap, which can be used to confine both antiprotons and Th- ions. The presented ion dynamics simulations show that the laser-cooled Th- anions can effectively cool antiprotons to a temperature around 10 mK

The unusual quadruple bonding of nitrogen in ThN

Abstract Nitrogen has five valence electrons and can form a maximum of three shared electron-pair bonds to complete its octet, which suggests that its maximum bond order is three. With a joint anion photoelectron spectroscopy and quantum chemistry investigation, we report herein that nitrogen presents a quadruple bonding interaction with thorium in ThN. The quadruple Th≣N bond consists of two electron-sharing Th-N π bonds formed between the Th-6d xz/6d yz and N 2p x/2p y orbitals, one dative Th←N σ bond and one weak Th←N σ bonding interaction formed between Th-6d z 2 and N 2s/2p z orbitals. The ThC molecule has also been investigated and proven to have a similar bonding pattern as ThN. Nonetheless, due to one singly occupied σ-bond, ThC is assigned a bond order of 3.5. Moreover, ThC has a longer bond length as well as a lower vibrational frequency in comparison with ThN