Observing chemical reactions in ultra slow motion

At ultra-low temperatures, molecules have so little energy that, in effect, their reactivity is slowed down

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A chemical reaction, simply stated, is the conversion of reactants into products. Consider the following simple chemical reaction where nitrogen dioxide decomposes into nitric oxide and oxygen.

2NO2 -> 2NO + O2

This reaction, in reality, is believed to progress in two steps as shown below

2NO2 -> NO3  NO

NO3 -> NO + O2

However, only the products NO and O2 can be detected. This is because, in the first intermediate step of the reaction, the production of NO3 + NO is transient and takes place within, literally, no time. Instantaneously, NO3 decomposes into NO2 + O2. Therefore, measure of transient intermediate steps of a chemical reaction is very difficult and in many cases, impossible. Knowledge of these intermediate steps of a chemical reaction is very useful. This will allow “quantum-state control” over the outcome of chemical reactions of interest to us.

Researchers have now come closer to achieving this quantum-state control by directly observing transient intermediates in a chemical reaction. They achieved this feat by cooling down the reaction to almost “absolute zero degree kelvin”. At this ultra-low temperatures, molecules have slow little energy that, in effect, their reactivity is slowed down. Therefore, an otherwise transient intermediate will become stable for a longer time in ultra-cold conditions. 

Researchers trapped potassium-rubidium gas molecules in a chamber at an extremely low temperature of only 500 x 10-9 kelvin or 500 nanokelvin. In this chamber, gas molecules were constantly reacting with each other. researchers were able to detect the intermediate K2Rb2 molecules for the first time along with the reactants and products as per the following reaction.

2KRb -> K2Rb2 -> K2 + Rb2

According to the author’s who performed these experiments and published it in Science, this research opens up many avenues. Specifically, in quantum mechanics which is a field of science that is used in engineering and machine designing.

This article was first published on 05 Dec, 2019 and last updated on 14 Jun, 2020.
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