Two-component Calculations for Polyatomic Hydrides and Fluorides Containing Superheavy Elements 113 and 114

Sang-Kil Son, Young-Kyu Han, and Yoon Sup Lee

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Superheavy elements have become the center of interest in theoretical chemistry for their unusual trends on the periodic table. Element 113 and 114 which have not been synthesized yet have 7s² 7p_1/2¹ and 7s² 7p_1/2² valence configurations, respectively. Considerable changes of molecular structures, vibrations, and stabilities are expected from spin-orbit interactions for molecules containing these superheavy elements since the p_1/2 valence is stabilized by enormous 7p spin-orbit splitting. For MX, MX₃ (M=Tl, 113, X=H, F), MX₂, MX₄ (M=Pb, 114, X=H, F), we performed geometry optimizations and normal mode analysis at the HF level of theory, and evaluated the stabilities at the CCSD(T) level using relativistic effective core potential with and without spin-orbit interactions. Spin-orbit coupling contracts the bond lengths for all cases and the bond contraction is more significant for the hydrides than the fluorides. Normal mode analyses reveal that molecular shapes of 113 and 114 molecules are analogous to Tl and Pb ones except for 113H₃ and 113F₃, and changes for vibrational frequencies of the hydrides are substantial. Spin-orbit interactions reduce bond energies by about 10–50 kcal/mol. The bonds become very weak and, in particular, element 114 seems to be chemically inert. These results can be explained by the stabilization and the relativistic radial contractions of the p_1/2 valence spinor by spin-orbit splitting.

Tags: superheavy element, spin-orbit effect, ECP, RECP, KAIST

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