Molecules Get Superchilly Reaction: Experiments, Theory Illuminate Ultracold Quantum Chemistry

Article excerpt

Researchers have now been able to stop and start chemical reactions between molecules at temperatures colder than the depths of outer space. And a new theoretical description helps explain the quantum mechanical details of how these reactions happen.

The details, presented March 17, offer glimpses into the burgeoning field of ultracold physics (SN: 12/20/08, p. 22).

Deborah Jin and Jun Ye of the University of Colorado at Boulder and the JILA research center in Boulder led experiments using lasers and electric fields to manipulate reactions between ultracold potassium-rubidium molecules.

"It's a beautiful demonstration of how quantum mechanics works," said chemist Jeremy Hutson of the University of Durham in England. The new studies reveal strange quantum effects "in a very simple regime that's never been explored before."

Jin, Ye and colleagues used lasers to cool the potassium-rubidium molecules, halting nearly all their usual frenetic motion. Held in this chilly "ground state" at a temperature around 200 nanokelvins, the molecules moved incredibly slowly, Ye said. But after a second or so, they started to disappear by twos.

"What's going on here is chemistry," Jin says. The potassium-rubidium molecules can interact with each other to form molecules made up of two potassium atoms and two rubidium atoms, the team reported in the Feb. 12 Science.

At the meeting, Jin and Ye presented new preliminary results showing not only that these chemical reactions occur, but that they also can be sped up or halted. Potassium-rubidium molecules have electric charges at each end-slightly negative at the potassium atom and slightly positive at the rubidium atom. …