Majorana, Pauling and the quantum theory of the chemical bond

TL;DR

This paper explores early 20th-century insights by Majorana on quantum chemical bonding, emphasizing exchange interactions and their relevance to modern molecular physics, with a focus on H2 and He2+ molecules.

Contribution

It highlights Majorana's pioneering work on exchange interactions in chemical bonds, contrasting his methods with Pauling's and discussing their significance today.

Findings

Majorana's exchange interaction approach to chemical bonds.

Analysis of He2+ molecular ion formation.

Proposal of ionic structures in homopolar molecules.

Abstract

We discuss in detail very little known results obtained by Majorana as early as 1931, regarding the quantum theory of the chemical bond in homopolar molecules, based on the key concept of exchange interaction. After a brief historical overview of the quantum homopolar valence theory, we address the intriguing issues of the formation of the helium molecular ion, He2+, and of the accurate description of the hydrogen molecule, H2. For the first case, the group theory-inspired approach used by Majorana is contrasted with that more known followed by Pauling (and published few months after that of Majorana), while for the second case we focus on his proposal concerning the possible existence of ionic structures in homopolar compounds, just as in the hydrogen molecule. The novelty and relevance of Majorana's results in the modern research on molecular and chemical physics is emphasized as well.