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Harvard Scientists Probe Coolest Reaction Possible

Researchers cooled down molecules to super-low temperature to ascertain reaction pathway & detect intermediate. They observed something that they didn’t expect.

Photo: Physics World

Do you know which place on this planet has the lowest temperature? Dome Argus & Dome Fuji at East Antarctic plateau. In 2010, NASA analyzed 32 years’ of data & concluded that -93.2 °C (or 179.95 K) is the minimum temperature recorded at this place. That’s the lowest temperature detected globally on record. But in our observable universe, the average temperature is 2.73 K which is much smaller than that measured on this planet. This steers human beings to think about how to attain a more frigid temperature than this. The threshold is -273.149 °C (or 0 K) & Quantum mechanics hypothesize no lesser possible temperature than 0 K. It is called the Absolute Zero temperature.

So, human maneuvers were directed to achieve the lowest possible temperature & in 2003, MIT researchers succeeded to attain 500 picoKelvin (a half-billionth of 1 K) temperature, remarkably close to the Absolute Zero. Although cooling down to arctic temperatures is curiosity-driven, but its impacts are far-reaching. It has promising applications in various fields, like quantum computing, ultrafast laser spectroscopy, modeling of quantum phases, etc. to name a few.

Photo: Harvard University

A group of researchers, led by Prof. Kang-Kuen Ni, at Harvard University has pioneered cryogenic endeavors in detecting transient reaction intermediates & curating reaction pathways. They managed to cool a set of KRb molecules down to 500 nanoKelvin for the first time. At such a gelid temperature, those molecules moved at a snail’s pace whose activities could eventually be controlled using high-intensity lasers.

KRb molecules were allowed to react bimolecularly using a pair of Raman laser beams which enabled researchers to assemble them to an energy-rich intermediate state, K2Rb2*. Finally, the intermediate was permitted to yield products, K2 & Rb2 molecules. Cryogenic temperature prolongs the half-life of reaction intermediates & eases detection of it using general detection methods. The findings were published in Science.

Using a photo-ionization detector, all three discernable species, reactant, intermediate & product molecules, were spotted simultaneously which validates the path predicted theoretically. Another pair of hypothetically anticipated intermediates couldn’t be observed through the detector & endorses only one path for reaction proceeding.

Without such an extraordinarily low temperature, perceiving intermediates & elucidation of reaction path would have been arduous as chemical reactions take place within a few picoseconds, a trillionth of a second. At slightly higher temperatures, say even at 1–2 K, intermediate lifespan plunges sharply, making it impossible to observe with commonly used detection techniques. Stagnating molecules & extending intermediate lifespan have given deep insights into how reactions come about in the microscopic realm.

Photo: Gadgets To Use

This reaction is also termed as one of the smallest chemical experiments ever conducted. But what does it mean from a layman’s perspective? Let’s assume you’re watching a movie at 1x speed in which a person is commuting from point A to point B on a bus. The person is moving on from point A & embussed (reactant molecules collide with each other). The bus carries them from their source to their destination. Bus & the person ensemble augment the transient intermediate system at the quantum level.

Upon reaching their destined stoppage, they got off the bus (intermediate starts breaking) & walks to point B (intermediate shatters yielding products). But what the ultra-cold temperature is doing in the experiment? As we envisioned, the movie clip was being played at 1x speed. Now, imagine you reduce the video playback speed to 0.1x. Every scene will be damn sluggish & shots would last much longer. You can notice every minuscule detail from each scene that you missed previously. The same thing is simulated at the atomic scale in this experiment.

Photo: Scientific American

But devising such an experiment comes at an exorbitant price & it’s made dearer because of high sophistication. Despite that, this experiment has opened the door for a much more detailed exploration of chemical reactions. The team is currently probing how to influence or even manipulate reaction pathways nudging molecules externally.

Being able to see what’s happening in the atomic-scale during a chemical reaction is exciting & conveying scientists invaluable data about the mechanistic approaches. Not just observation, but the extended time window would allow researchers to intervene in reactions & lead these in their desired way. That’ll surely open a whole new bunch of applications in natural sciences & the scientific community is looking forward to learn what emerges next.




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Sumon Basak

Sumon Basak

Full time chemist. Part time writer. No longer writing on Medium. Committing time to writing research for laypeople at

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