Rydberg Molecule moves from theory to fact

The theoretical Rydberg molecule has been formed. This new kind of molecule is formed through an 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 which can trap another nearby atom into a very distant chemical bond. The Rydberg molecules in question were formed from two atoms of rubidium - one a Rydberg atom with a distant electron, and one a "normal" atom.

The experiments use an ultracold cloud of rubidium bringing the atoms in the gas closer together as they cool. They then excite an atom to the "Rydberg state" using a laser. At temperatures very close to absolute zero the critical bonding distance of about 100nm between the atoms is reached. This gap is vast compared to ordinary molecules.

"The Rydberg electron resembles a sheepdog that keeps its flock together by roaming speedily to the outermost periphery of the flock, and nudging back towards the centre any member that might begin to drift away," said one of the exerpimenters, Professor Greene. Pushing this electron out to its distant periphery to make a Rydberg atom requires energy. "We excite the atoms to the Rydberg stage with a laser," explained Dr Bendkowsky.

See BBC News.