Researchers have observed something which had been proposed for a long time: butterfly Rydberg molecules.
"This new binding mechanism, in which an electron can grab and trap an atom, is really new from the point of view of chemistry," explained lead researcher Chris Greene. "It's a whole new way an atom can be bound by another atom."
The atom can be a strange thing to describe, but for the sake of simplicity, let's imagine it as a proton and neutron core surrounded by an electron cloud. In Rydberg molecules, the electron is kicked far far away from the nucleus, but still orbits it. In 2002, a team of researchers from Purdue University in Indiana predicted that a Rydberg molecule could attract and bind to another atom -- something which at the time was thought to be impossible. Now, they've proven this theory.
"For all normal atoms, the electrons are always just one or two angstroms away from the nucleus, but in these Rydberg atoms you can get them 100 or 1,000 times farther away," Greene said. "Following preliminary work in the late 1980s and early 1990s, we saw in 2002 the possibility that this distant Rydberg electron could bind the atom to another atom at a very large distance. This electron is like a sheepdog. Every time it whizzes past another atom, this Rydberg atom adds a little attraction and nudges it toward one spot until it captures and binds the two atoms together."
While this is exciting in itself, the implications for chemical studies are hard to fathom at this point. Basically, it's an entirely new way through which two or more atoms can be bound together and this can open a world of possibilities. However, this transformation requires special conditions. In order for this to happen, Greene and the rest of his team had to cool Rubidium gas almost to absolute zero, the absolute lowest temperature in the universe. After that, they pushed the electron far from its nucleus using a laser, and then they observed it.
"Whenever another atom happens to be at about the right distance, you can adjust the laser frequency to capture that group of atoms that are at a very clear internuclear separation that is predicted by our theoretical treatment," Greene said.
It's also very satisfying and encouraging to validate the entire theoretical process. There's something exhilarating in predicting something theoretically, and then observing it in practice.
"It's a really clear demonstration that this class of molecules exist," Greene said. "It also validates the whole theoretical approach that we and a few other groups have taken that led to the prediction and study of this new class of molecules.
Tests continue to see what kind of molecules can be created through this process and what the potential applications are.
The research has been published in the journal Nature Communications.