A molecule that until now existed only in theory has finally been made.
Known as a Rydberg molecule, it is formed through an elusive and extremely weak chemical bond between two atoms.
The new type of bonding, reported in Nature, occurs because one of the two atoms in the molecule has an electron very far from its nucleus or centre.
It reinforces fundamental quantum theories, developed by Nobel prize-winning physicist Enrico Fermi, about how electrons behave and interact.
The Rydberg molecules in question were formed from two atoms of rubidium – one a Rydberg atom, and one a “normal” atom.
The movement and position of electrons within an atom can be described as orbiting around a central nucleus – with each shell of orbiting electrons further from the centre.
A Rydberg atom is special because it has one electron alone in an outermost orbit – very far, in atomic terms, from its nucleus.
Back in 1934 Enrico Fermi predicted that if another atom were to “find” that lone, wandering electron, it might interact with it.
“But Fermi never imagined that molecules could be formed,” explained Chris Greene, the theoretical physicist from the University of Colorado who first predicted that Rydberg molecules could exist.