The Cyanopolyyne Long Chain Molecules
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.
David and hk
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.
Alex was an outstanding student undergraduate and he did a great job. He obtained microwave microwave, infrared and 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 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 and probably most importantly this spectrum led to our detection of the long carbon chains in space and of course thirdly to the experiment which uncovered the existence of C 60 and it’s possible contender as a carrier of the diffuse interstellar bands.
Oh for the days before computers when our spectra were printed out on chartpaper!