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Wednesday 9 December 2020

One Nobel Prize Later...

The Nobel-prize winning buckminsterfullerene, C60, discovery took place in September 1985. Its discoverers were Professor Harry Kroto, along with Richard Smalley and Robert Curl – but this wasn’t what they were looking for.
NASA, ESA, and A. Simon (Goddard Space Flight Center)

Kroto was interested in space. He was working on carbon-based molecules that could be detected in interstellar space using radio telescopes... and he thought he’d found good evidence for cyanopolyynes, molecules based on a chain of carbon and nitrogen atoms, but he still didn’t know how they were made. Kroto had had a good think about it, though, and one idea he had was that they were made by red giants, or near them. He’d have to test his theory, but how?

Smalley and Curl had a laser-generated supersonic cluster beam for their research on semiconductors; this had the potential to heat something up hotter than the surface of most stars. Kroto thought doing this to a bit of carbon would be a fantastic idea, and would potentially make a whole bunch of new stuff, including the mysterious cyanopolyynes. He persuaded them to let him have a go.

As the vapour cooled and new compounds settled out of the hot mess, mass spectrometry revealed that there were indeed cyanopolyynes present – and buckminsterfullerenes. Kroto, Smalley and Curl got a Nobel prize, and cyanopolyyne science took a small step forward.

But, believe it or not, people are still exploring the mechanisms for cyanopolyyne formation in space today.

The most basic cyanopolyyne is HC3N, with only three carbons. The longer the chain, the bigger and more complicated the cyanopolyyne, the less we know about how it forms. The existence of HC7N and HC11N are even doubted (not because there isn’t evidence, but because it’s possible the evidence is for something similar but different).
Buckminsterfullerene Wikipedia via Mstroeck and Bryn C.

These molecules are seen both in “hot cores” and in the cold environs of outer space, and these need different theories to explain them[1].

Normally most chemical reactions are explained by the interactions between ions and molecules, but this doesn’t work for most of the HC3N molecules in space, let alone longer ones[2][3]! It’s just too cold (10K or -263oC) and molecules are too far apart to make reactions likely.

The cyanopolyynes may form via radical chain polymerisation – similar reactions to those that happen in our atmosphere with species such as methane and ozone (and CFCs…). Reactions may be activated by ultraviolet light, and take over 1 million years.

And, one Nobel prize later, that’s still pretty much all we know.

why don't all references have links?

[1] Chapman, J. F., et al. Cyanopolyynes in hot cores: modelling G305. 2+ 0.2. Monthly Notices of the Royal Astronomical Society 394.1 (2009): 221-230.
[2] Fukuzawa, Kaori, and Yoshihiro Osamura. Molecular orbital study of neutral-neutral reactions concerning HC3N formation in interstellar space. The Astrophysical Journal 489.1 (1997): 113.
[3] Kroto, H. W. Chains and grains in interstellar space. Polycyclic aromatic hydrocarbons and astrophysics. Springer, Dordrecht, 1987. 197-206.

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