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

Abstract

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 ~298kcal/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. 22kcal/mol and the exothermic reaction energy is ca. 28kcal/mol [(U)MP2/6–311+G(d)].