Infrared Spectra of UF_n (n = 1-4) in Solid Ne and Ar Matrices: Symmetry-Breaking D_2d Structure of UF₄.

Authors

Jianfeng Lin, Chaofan Li, Zhiming Li, Xuefeng Wang, Haijun Dang, Wenli Zou, Zhichao Liu, Yue Ma, Junwei Yang, Haitao Zhang, Qiang Jin, Zongyuan Chen, Bingbing Suo, Xiaowei Yi, Zhijun Guo

Published in

The journal of physical chemistry. A. Jun 13, 2025. Epub Jun 13, 2025.

Abstract

This study addresses two persistent challenges in uranium fluoride chemistry: resolving decades-long spectral assignment conflicts across UF₂, UF₃, and UF₄ species, and conclusively settling the symmetry controversy of UF₄. By the cryogenic matrix isolation IR spectroscopy technique in combination with relativistic quantum chemical calculations, we experimentally tracked the stepwise formation of UF to UF₆ in neon and argon matrices. Theoretical validation has led to a reassignment of the infrared absorption bands for UF₂, UF₃, and UF₄, defining their molecular geometries. While UF₂ exhibits a V-shaped C_2v structure and UF₃ has a pyramidal C_3v configuration, UF₄ adopts a D_2d geometry rather than a T_d symmetry, arising from the Jahn-Teller distortion, which was verified by complete active space second-order perturbation theory (CASPT2) calculations incorporating spin-orbit coupling, supporting predictions from relativistic density functional theory and BW-MRCCSD calculations by Johnson et al. Moreover, weak van der Waals interactions between UF_n (n = 2-4) and argon atoms induced vibrational redshift. Bonding analyses revealed that U-F bonds in UF_n (n = 1-6) possess dual ionic-covalent character, with ionic contributions of 78-88%. The covalent enhancement in fluorides arises from the overlap of U 5f/6d orbitals with F 2p orbitals and their near-degeneracy. These findings reconcile historical discrepancies, establish definitive benchmarks, and advance uranium fluoride chemistry for nuclear fuel applications.

PMID:
40512972
Bibliographic data and abstract were imported from PubMed on 14 Jun 2025.

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