Relativistic all-electron Dirac–Fock calculations on RnF6 and its ions

Prediction of stable radon fluoride molecules and geometry optimization using first-principles calculations

Noble gases possess extremely low reactivity because their valence shells are closed. However, previous studies have suggested that these gases can form molecules when they combine with other elements with high electron affinity, such as fluorine. Radon is a naturally occurring radioactive noble gas, and the formation of radon-fluorine molecules is of significant interest owing to its potential application in future technologies that address environmental radioactivity. Nevertheless, because all isotopes of radon are radioactive and the longest radon half-life is only 3.82 days, experiments on radon chemistry have been limited. Here, we study the formation of radon molecules using first-principles calculations; additionally, possible compositions of radon fluorides are predicted using a crystal structure prediction approach. Similar to xenon fluorides, di-, tetra-, and hexafluorides are found to be stabilized. Coupled-cluster calculations reveal that RnF₆ stabilizes with O_h point symmetry, unlike XeF₆ with C_3v symmetry. Moreover, we provide the vibrational spectra of our predicted radon fluorides as a reference. The molecular stability of radon di-, tetra-, and hexafluoride obtained through calculations may lead to advances in radon chemistry.

A Computational Study on Closed-Shell Molecular Hexafluorides MF6 (M=S, Se, Te, Po, Xe, Rn, Cr, Mo, W, U) - Molecular Structure, Anharmonic Frequency Calculations, and Prediction of the NdF6 Molecule

Quantum chemical methods were used to study the molecular structure and anharmonic IR spectra of the experimentally known closed-shell molecular hexafluorides MF₆ (M=S, Se, Te, Xe, Mo, W, U). First, the molecular structures and harmonic frequencies were investigated using Density Functional Theory (DFT) with all-electron basis sets and explicitly considering the influence of spin-orbit coupling. Second, anharmonic frequencies and IR intensities were calculated with the CCSD(T) coupled cluster method and compared, where available, with IR spectra recorded by us. These comparisons showed satisfactory results. The anharmonic IR spectra provide means for identifying experimentally too little studied or unknown MF₆ molecules with M=Cr, Po, Rn. To the best of our knowledge, we predict the NdF₆ molecule for the first time and show it to be a true local minimum on the potential energy surface. We used intrinsic bond orbital (IBO) analyses to characterize the bonding situation in comparison with the UF₆ molecule.

Calculated optical and magnetic properties of hexafluorouranate (V) anion: UF[sub 6][sup −]

Our ab initio all-electron Dirac-Fock and the corresponding nonrelativistic limit calculations performed at four U-F bond distances yield for octahedral UF(6) (-) the optimized U-F bond distance of 2.091 and 2.088 A, respectively. We have also performed Dirac scattered wave calculations at the optimized U-F bond distances using the first-order pertubational procedure to obtain the Zeeman and hyperfine magnetic tensors for the octahedral anion UF(6) (-). The calculated isotropic Zeeman tensor of Deltag=-2.87 is in fairly good agreement with the value of Deltag=-2.78+/-0.10 obtained in electron spin resonance experiments on the H(3)O(+)UF(6) (-) adduct and the unpaired electron-spin spends approximately 2.5% of its time on the fluorine 2p(3/2) spinors. The calculated relativistic transition energies of the near-IR and visible absorption bands are also in good agreement with the experimental results. The octahedral uranium hexafluoride anion has a simple crystal field f(1) configuration; however, relativistic four-component wave functions are necessary to interpret correctly the available magnetic data, while a relativistic treatment taking into account double group symmetrized basis functions should suffice for the interpretation of the optical data.