Where to place the positive muon in the Periodic Table?

TL;DR

This study investigates whether positively charged muons can form atomic structures similar to protons in molecules, using advanced quantum calculations, and concludes that muons are structurally and chemically akin to protons, deserving placement in the hydrogen group of the Periodic Table.

Contribution

The paper provides a comprehensive quantum analysis demonstrating muons can form atomic basins similar to protons, supporting their placement alongside hydrogen in the Periodic Table.

Findings

Muons can form atomic basins similar to protons.

The properties of muonic AIM are comparable to protonic AIM.

Muons are structurally and bonding-wise similar to hydrogen in molecules.

Abstract

In a recent study it was suggested that the positively charged muon is capable of forming its own "atoms in molecule"s (AIM) in the muonic hydrogen-like molecules, composed of two electrons, a muon and one of the hydrogen isotopes, thus deserved to be placed in the Periodic Table [Phys. Chem. Chem. Phys. 16, 6602, 2014]. In present report, the capacity of the positively charged muon in forming its own AIM is considered in a large set of molecules replacing muons with all protons in the hydrides of the second and third rows of the Periodic Table. Accordingly, in a comparative study the wavefunctions of both sets of hydrides and their muonic congeners are first derived beyond the Born-Oppenheimer (BO) paradigm, assuming protons and muons as quantum waves instead of clamped particles. Then, the non-BO wavefunctions are used to derive the AIM structures of both hydrides and muonic congeners within context of the multi-component quantum theory of atoms in molecules. The results of the analysis demonstrate that muons are generally capable of forming their own atomic basins and the properties of these basins are not fundamentally different from those AIM containing protons. Particularly, the bonding modes in the muonic species seem to be qualitatively similar to their congener hydrides and no new bonding models is required to describe the bonding of muons to a diverse set of neighboring atoms. All in all, the positively charged muon is similar to proton from structural and bonding viewpoint and deserved to be placed in the same box of hydrogen in the Periodic Table. This conclusion is in line with a large body of studies on the chemical kinetics of the muonic molecules portraying the positively charged muon as a lighter isotope of hydrogen.