Heavy atom tunnelling on XeF₆ pseudorotation.

Area of Science:

• Quantum chemistry
• Inorganic chemistry
• Spectroscopy

Background:

• The precise molecular geometry of Xenon hexafluoride (XeF₆) has been a long-standing enigma for over 50 years.
• The Jahn-Teller effect was previously implicated in the complex, elusive C_3v minima observed in XeF₆.

Purpose of the Study:

• To theoretically investigate the dynamic behavior and rearrangement mechanisms of XeF₆.
• To explore the quantum mechanical tunneling phenomenon in XeF₆ and its isoelectronic analogs.
• To provide a theoretical basis for experimental observation of tunneling in XeF₆.

Main Methods:

• Theoretical calculations were employed to model the potential energy surface and reaction pathways of XeF₆.
• Quantum mechanical tunneling rates were computed for XeF₆ and its isoelectronic anions IF₆^- and TeF₆^2-.
• A comprehensive isotopic analysis was performed, including the calculation of kinetic isotope effects.

Main Results:

• Theoretical evidence confirms genuine fluorine quantum mechanical tunneling rearrangement in XeF₆, enabling rapid isomer interconversion even near 0 K.
• Isoelectronic species IF₆^- and TeF₆^2- exhibit similar tunneling behavior, but with lower energy barriers and faster rates.
• A significant kinetic isotope effect was observed for the k(¹⁸F)/k(¹⁹F) ratio, supporting the tunneling mechanism.

Conclusions:

• XeF₆ undergoes rapid intramolecular rearrangement via quantum mechanical tunneling, resolving decades of geometric uncertainty.
• The tunneling dynamics are influenced by the energetic barrier height, with related anions showing accelerated rates.
• Experimental observation of this tunneling effect in XeF₆ is proposed using cryogenic Nuclear Magnetic Resonance (NMR) or Infrared (IR) spectroscopy.