Electrons are the drivers of chemistry. They form the chemical bonds that connect atoms into complex molecules. When they move around, they break bonds, create new bonds, and transform molecules into different ones. When chemists hone their intuition for categorizing and predicting the results of chemical reactions (as described in the 2019 PT column “How to succeed in orgo without really trying ”), most of what they ask themselves is, Where are the electrons inclined to go?
The chemist’s mental picture is merely a heuristic. Experiments have never observed the real-time and real-space flow of electrons during a chemical reaction. But now researchers led by Dao Xiang, of Shanghai Jiao Tong University in China, have taken a step toward filming an electron reaction movie. 1 For their proof-of-principle experiment, they studied the photodissociation of ammonia, illustrated in figure 1 : A laser pulse hits an NH3 molecule and rips off one of its hydrogen atoms. The researchers probe the dissociating molecules with precisely timed blasts of electrons, which scatter off the molecular nuclei and electrons and give information about their whereabouts.
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