Categories: Chemistry in History , Guest posts |  Comments
Guest post by Rowena Fletcher-Wood
Among the many accidental discoveries through the ages is an experiment designed to probe carbon molecules in space, which unearthed a new terrestrial molecule.
It all happened in an 11-day whirl, between 1 September 1985, when Harry Kroto first arrived at Rice University, US, and 12 September, when he, along with Richard Smalley and Robert Curl, submitted a paper to Nature: ‘C60 Buckminsterfullerene’. Eleven years later, in 1996, the three were awarded the Nobel prize for chemistry.
Indeed, a Nobel prize may have been some consolation to Smalley and Curl, who were initially reluctant to delay their research on silicon and germanium semiconductors to let Kroto play with carbon. Kroto was exploring a completely different area of research: cyanopolyynes, alternating C–N chains detected in interstellar space using radiotelescopes. Although the evidence for their existence was good, the origin of these compounds was still unknown. Kroto postulated that they may form in the vicinity of red giants, and wanted to use Smalley’s laser-generated supersonic cluster beam to recreate this high-heat atmosphere and uncover mechanisms for their formation.
After agreeing to let Kroto use the apparatus, the three scientists, helped by graduate students James Heath, Sean O’Brien and Yuan Liu, loaded a graphite disk onto the beamline in a helium chamber and vaporised it into a plasma at temperatures exceeding the surface temperatures of most stars. Under high pressure helium, the vapour cooled and condensed, forming new interatomic bonds and aligning into different-sized clusters, which were immediately pulse ionised and swept into a mass spectrometer for analysis.
First, the students found Kroto’s expected carbon snakes, but then they noticed a distinct peak at C = 60 and a smaller one at C = 70. The abundance of C60, and increasing yield under higher pressure conditions suggested a very stable, closed-shell macromolecule. Unlike Kekulé’s benzene ring, buckminsterfullerene was not identified through dreaming, but through the resourceful application of sticky tape and cardboard cut outs. The model was proposed: a truncated icosahedron, consisting of twenty hexagons and twelve pentagons, like a carbon football. The name, buckminsterfullerene, was inspired by the architect famous for his similar-looking geodesic domes.
Since then, enthusiastic exploration into other fullerene allotropes has revealed that we could have accidentally discovered buckyballs long ago using much lower-tech equipment: a burning candle produces buckyballs in its soot by vaporising wax molecules. Not only that, but buckyballs occur in geological formations on Earth and, since 2010, have been detected in cosmic dust clouds. The ball-like carbon molecule wasn’t even a new idea: between 1970 and 1973, three independent research groups led by Eiji Osawa of Toyohashi University of Technology, R W Henson of the Atomic Energy Research Establishment, and D A Bochvar of the USSR, predicted the existence of the C60 molecule and calculated its stability. However, their work was purely theoretical, and didn’t get the attention it deserved. Buckyballs were discovered, rather than made, so perhaps it’s not surprising that they were found by accident: more surprising is that that weren’t found before.