A super-sized atom plus a cold ion have been combined to make a completely new molecule that is 4 micrometres across and makes extremely long molecular bonds.
A completely new kind of molecule has been made by combining an extremely cold ion and a super-sized atom. The unusual molecular bond between the two was thousands of times longer than bonds in most room temperature molecules, and the method to make and study it could kickstart a new branch of ultracold quantum chemistry.
Molecules form when atoms or groups of atoms share electrons or stick together because they are caught in each other’s electric fields. Tilman Pfau at the University of Stuttgart in Germany and his colleagues have now created giant ultracold molecules by controlling electric forces between super-sized rubidium atoms and normal-sized rubidium atoms that have extra electric charge.
The team started with a cloud of rubidium atoms cooled to a millionth of a degree Celsius above absolute zero. The researchers then used a laser beam to remove an electron from a single rubidium atom which turned it into a positively charged ion.
Next, they used another laser to add energy into a different atom which made its outermost electrons move far from the nucleus and stretch the whole atom out to an unusually large size.
Because these far-out electrons are extremely sensitive to presence of electric charges, the giant atom could not escape the influence of the ion. The two became bound in a molecule roughly four micrometres long, a few times longer than some bacteria and a hundred times larger than a molecule of carbon dioxide.
Each such molecule, and the molecular bonds that keep it together, are the first of their kind, says Johannes Denschlag at Ulm University in Germany, who was not involved in the experiment. “In chemistry we learn that there are a handful of binding mechanisms which are responsible for the structure of the material world around us. But, of course, our world is much richer,” he says. “It is exciting to find novel ways for making chemical bonds.”
Pfau says that his team spent four years developing a special microscope to be able to see the quantum processes that only happen between extremely cold atoms and ions. His team used this so-called ionic microscope, which quickly applies an electric field to the new molecules to make them fly onto a detector, to confirm and observe the formation of the new type of molecular bond.
Hossein Sadeghpour at Harvard University says that being able to create new molecules and study them with the ionic microscope may lead to research in a previous unexplored type of ultracold quantum chemistry. Researchers had theoretical ideas about doing so in the past, but the new experiment demonstrated fantastic tools for actually making it happen, he says.
Reference:
Zuber, N., Anasuri, V.S.V., Berngruber, M. et al. Observation of a molecular bond between ions and Rydberg atoms. Nature 605, 453–456 (2022). DOI: 10.1038/s41586-022-04577-5