The Birth of a CO₂ Molecule

Using a scanning tunneling microscope (STM), a device that takes pictures at the atomic level, scientists have witnessed how carbon dioxide (CO₂) forms in a common chemical reaction, in which carbon monoxide (CO) reacts with atoms of oxygen (O) to yield CO₂. These single-molecule experiments have already provided important chemical insights that may lead to better automobile emission control, air purification, and chemical sensing.

Panel (A) of the above figure shows an isolated carbon monoxide atom
adsorbed on a silver surface. Panel (B) shows a pair of oxygen atoms on
the surface. (C) shows CO and two O atoms separated When the two
species are positioned to react with one another they form (E) an
intermediate O-CO-O complex, which had not been previously observed.
The O-CO-O complex ultimately leads to the formation of a CO2 atom,
and an oxygen. Panels (D) and (F) shows the arrangement of oxygen and
CO for panels (C) and (E) respectively.

Reaction of a carbon monoxide (CO) molecule released from an STM tip with an oxygen atom on the surface. In (A), a CO molecule is on the STM tip. The image shows two O atoms. (B) shows the STM's "tunneling" current during the time in which a voltage is applied to make the CO atom leave the tip and react with an oxygen atom to form a CO₂ molecule. Panel (C) shows an image of the area after the reaction. (D), (E), and (F) are schematic diagrams for (A), (B), and (C) respectively.

Reported by: J.R. Hahn and Wilson Ho, Physical Review Letters, 15 October 2001.

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