Microwave spectra of the cyanopolyynes
In 1973, Sir Harry Kroto and his colleague David Walton created a degree by thesis project for undergraduate student, Alec Alexander. The project entailed the synthesis of long carbon chain molecules.
Sir Harry Kroto's reflections
"In 1973, my colleague David Walton and I put together a degree by thesis project for an undergraduate, Alec Alexander. The project entailed the synthesis of long carbon chain molecules starting with HC5N which would be very easy to detect by microwave spectroscopy as it would have a big dipole moment.
David was an expert in coupling acetylenes together and had made a chain with 32 carbon atoms. That really impressed me.
Sir Harry Kroto
"In retrospect, it can be seen that the project which David and I put together in 1973 for the chemistry by thesis course at the University of Sussex to study long carbon chain molecules, was a seed which eventually led to the discovery of the C60 molecule and ultimately its detection in space.
"Alec was an outstanding undergraduate student and he did a great job. He obtained microwave infrared NMR spectra of various chains.
"The original idea was to study the simplest possible chain molecules and study their molecular dynamics in particular the vibrational motion. I wondered whether one can obtain information on how quantum mechanical dynamics might change as the vibrational quantum number increased and one would approach the classical limit.
"As it turned out quantum mechanics worked very well indeed for the vibrational states we were able to reach. Perhaps my all time favourite spectrum, that of HC5N, is shown here, partly because it was the first spectrum obtained on my new (then) microwave spectrometer which arrived in 1974, partly because it is so beautiful showing 13 C and 15 N isotope substituted species and natural abundance.
"Most importantly this spectrum led to our detection of the long carbon chains in space and of course to the experiment which uncovered the existence of C60 and it’s possible contender as a carrier of the diffuse interstellar bands."
Download the Polyyne section of the Tilden lecture (4.23MB).
View the wide band trace of HC5N I (PDF, 4.05MB) and HC5N II (PDF, 1.94MB).