On Molecular Motion — Freezing Cold Molecules

If you’ve never thought about the temperature of molecules, these MIT researchers will have changed that fact. Cold molecules are now a plaything in MIT’s laboratory. In successfully cooling a gas of sodium potassium (NaK) molecules to a temperature of 500 nanokelvin (only a hair above absolute zero), they have done it — they have proven the theory griping scientists for decades.

The Molecular Motion Theory

Molecules surround us, in matter and space, in constant motion and interaction with one another. They move extremely fast, too. This is true of molecules at temperate temperatures. However, researchers have long suspected that if they were to be able to cool the temperature of a molecule to nearly absolute zero, the new cold molecules would subdue in a screeching halt, no longer frenzied in motion. The idea is that they would actually move more unanimously.

A Union of Cold Molecules

A less chaotic, more orderly moving molecular world is strange to consider. It’s so foreign because the reality is so different. No surprise there as collisions with other molecules were way less likely in their less frenzied, slowed motions. According to Physicists at MIT,  molecules “exhibited very strong dipole moments — strong imbalances in electric charge within molecules that mediate magnet-like forces between molecules over large distances.”

A professor in the physics department, Martin Zwierlein believes that with knowing normal temperature molecules are brimming with high energy, and the cold molecules become steadied, brings us closer to finding out the temperatures where quantum mechanics interacts hugely with the motion of molecules. In that case, these sodium potassium molecules would move like matter waves rather than randomly frenetically. Researchers have published their findings in Physical Review Letters.

On Molecular Motion -- Freezing Cold Molecules - Clapway

Sodium Potassium (NaK) Molecule Dumbbell

Every single molecule — even the simples of them — is made up of atoms bonded to form its structure. Imagine a dumbell with the weights on either end representing individual atoms. The bar is the bond that holds the structure together. At simplest, they are held together by electromagnetism. MIT researchers tested on and cooled sodium potassium (NaK) molecules. NaK’s structure included a single sodium atom and a single potassium atom.

How To Cool Molecules

It is easier to make cold molecules that have a simple sort of form, imaginably (they move so freely). The tools the MIT research team used included a cooling laser to evaporatively cool cloud of individual sodium and potassium atoms. They were then made to bond using an electromagnetic field. They did this with a Feshbach resonance.

The Feshbach resonance technique was invented by another MIT physicist named Herman Freshbach. It creates a rather weak bond, however. The MIT team strengthened the bond with another technique again involving lasers. It was with this technique they were able to bring down the temperature and frenetic movement to its lowest. The cold molecules were now relatively chemically stable, especially in their kinetic energy state. The sodium potassium (NaK) molecule gas turned out to be quite stable. Zweirlein says that now we’re at 500 nanokelvins and this is already an accomplishment. With that, 10 degrees colder is an ideal for the future.


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