Primary retention following nuclear recoil in β-decay: Proposed synthesis of a metastable rare gas oxide (³⁸ArO₄) from (³⁸ClO₄⁻) and the evolution of chemical bonding over the nuclear transmutation reaction path

Argon tetroxide (ArO₄) is the last member of the N=50 e^– isoelectronic and isosteric series of ions: SiO₄⁴⁻, PO₄³⁻, SO₄²⁻, and ClO₄⁻. A high level computational study demonstrated that while ArO₄ is kinetically stable it has a considerable positive enthalpy of formation (of ∼298 kcal/mol) (Lindh et al., 1999. J. Phys. Chem. A 103, pp. 8295–8302) confirming earlier predictions by Pyykkö (1990. Phys. Scr. 33, pp. 52–53). ArO₄ can be expected to be difficult to synthesize by traditional chemistry due to its metastability and has not yet been synthesized at the time of writing. A computational investigation of the changes in the chemical bonding of chlorate (ClO₄⁻) when the central chlorine atom undergoes a nuclear transmutation from the unstable artificial chlorine isotope ³⁸Cl to the stable rare argon isotope ³⁸Ar through β-decay, hence potentially leading to the formation of ArO₄, is reported. A mathematical model is presented that allows for the prediction of yields following the recoil of a nucleus upon ejecting a β-electron. It is demonstrated that below a critical angle between the ejected β-electron and that of the accompanying antineutrino their respective linear momentums can cancel to such an extent as imparting a recoil to the daughter atom insufficient for breaking the Ar–O bond. As a result, a primary retention yield of ∼1% of ArO₄ is predicted following the nuclear disintegration. The study is conducted at the quadratic configuration interaction with single and double excitations [QCISD/6−311+G(3df)] level of theory followed by an analysis of the electron density by the quantum theory of atoms in molecules (QTAIM). Crossed potential energy surfaces (PES) were used to construct a PES from the metastable ArO₄ ground singlet state to the Ar–O bond dissociation product ArO₃+O(³P) from which the predicted barrier to dissociation is ca. 22 kcal/mol and the exothermic reaction energy is ca. 28 kcal/mol [(U)MP2/6–311+G(d)]. - Highlights: • Mathematical model for the yield of primary retention after β-decay. • The nature of metastable chemical bonding in thermodynamically unstable compounds. • The changes in the nature of chemical bond upon nuclear transmutation. • Synthetic protocol of metastable rare gas oxides (ArO₄) from a hot chemistry route