CO2 production at the single-molecule level has been observed
for a specific chemical reaction. Rather than micromanage (or nanomanage)
compliance of the Kyoto Treaty, this new accomplishment instead offers
fundamental chemical details of CO2 formation which may bring
improvements to automobile emission control, air purification, and chemical
Using a scanning tunneling microscope (STM) as a "nanoreactor,"
researchers (Wilson Ho, UC-Irvine, 949-824-5234, firstname.lastname@example.org) studied
the oxidation of a single carbon monoxide (CO) molecule on a metal surface.
In this "catalytic oxidation reaction," CO combines with oxygen
(O) on the surface to form CO2.
Putting CO next to two oxygen atoms on a silver surface, the researchers
found that the CO and O species must be very close to each other to
react. When the CO is at the closest possible distance to an oxygen
atom on the surface, at just 1.78 angstroms away, the researchers saw
that the reactants form an intermediate O-CO-O complex, which has not
been observed to date (see images).
Then, tunneling electrons from the STM tip flow through the CO and O
species to bring the O-CO-O complex to a higher energy state and enable
it to transform into CO2 and a lone oxygen atom. (In a real-world
situation, heat rather than tunneling electrons would spur this transformation.)
In separate experiments investigating another pathway for the same
chemical reaction, the researchers put a CO molecule on the STM tip,
and then positioned it close to an O atom on a silver surface. In this
case, the CO and O loosen their respective bonds to the STM tip and
the silver surface. Eventually, both species are on the surface and
they interact to form CO2. In demonstrating this, they showed
that CO and O don't initially have to be on the surface to form CO2;
the CO can come from above. The researchers also ruled out the idea
that CO reacts with molecular oxygen (O2) on the surface
to form CO2; instead it only reacts with atomic oxygen. (Hahn
and Ho, Physical Review Letters, 15 October 2001.)