New molecules detected and studied using microwave and photoelectron spectroscopy techniques in synergistic combination.
The new molecules were mainly detected using twin techniques photoelectron and microwave spectroscopy in synergistic combination. A molecule might be more easily detected using one technique than the other and so using the two together often made success in detection more efficient. For instance it turned out to be very easy to detect the monomer of thioacetaldehyde by pyrolysis of the trimer by photoelectron spectroscopy (see image below) and piggyback on that result using microwave techniques (see image further below). Most of the molecules were detected in the products of a thrombolysis using a quartz tube furnace as shown just below. The overall approach is reviewed here: Tilden Lecture Intro
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 HC 5N 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 me. 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 student undergraduate and he did a great job. He obtained microwave 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 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.
The first detection and isolation of the phosphaalkenes eg CH2=PH and general methods for creating phosphaalkynes eg CH3C≡P
In 1964 when I arrived NRC I met to Takeshi Oka who told me about the molecule HCP the phosphorus analogue of HCN which a previous post-doc Kelvin Tyler had studied by electronic spectroscopy. It had been made several years before by Gierr. This really intrigued me because I thought that if HCP could be made then why not analogues such as for instance CH3CP. This was on my mind for nearly 10 years. When I got my own microwave spectroscopy spectrometer in 1974 I was in the coffee room one day and I consulted my colleague at the University of Sussex, John Nixon, to find out whether he had any likely precursors of double bonded and triple bonded carbon phosphorus molecules. A new research student Nigel Simmons was started on the project and almost immediately it was successful … a wide range of phosphaalkenes, a completely new class of molecules, and a wide range of new analogues of HCP (phosphaalkynes) which had never been made before.
I consider this paper one of the most intellectually satisfying contribution (perhaps the most) I have ever made as I thought it must be possible to make a carbon phosphorus double bonded molecules and it worked beautifully CH2PX c39760000513 (it has only ca 100 citations but it was the paper that gave birth to the general field of Phosphaalkene Chemistry! – so much for citations!)
The Detection of Unstable Molecules by Microwave Spectroscopy :
Phospha-alkenes CF2=PH, CH2=PCl, and CH2=PH
Ry MICHAEL J . HOPKINSON, HAROLD. KROTO, JOHN F. NIXON and NIGEL P . C. SIMMONS
(School of Molecular Sciences, University of Sussex, Brighton BN1 9Q J)
An overview of this program is summarised here Tilden Lecture CP Section
In the beautiful spectrum below we see that and CH3PCl2 thermalises is to form CH2PCl by eliminating one unit of HCL. Furthermore one sees rather nicely that 2 units are also eliminated to form HCP the only phosphaalkyne known before our general synthetic breakthrough.
General methods of creating thioaldehydes thioketones and boron sulphides etc MeCHS, CH2=C=S, CIBS
About 1970 I was trying to produce the new molecule thio formaldehyde from dimethyl disulphide by flash photolysis. Remember that at this time there was something called the double bond rule which indicated that molecules with double bonds between carbon and second and third row elements were either not makeable or unstable. However the mere fact that OCS is stable as CS2 suggests that this rule is unreliable. I had previously observed formaldehyde by pyrolysis of dimethyl peroxide. However dimethyl peroxide is much more easily photolysed than dimethyldisulphide. Just about this time I was at a conference in Dijon where Don Johnson from NBS presented a paper on this molecule which he had produced simply by using a Bunsen burner on a quartz tube through which he passed dimethyl disulphide and had detected it by microwave spectroscopy. I realised that this might be a general method to obtaining some semi-stable thioaldehydes and ketones and asked Don whether he was interested in going further along this avenue as I was. He said he was not and so was initiated a highly successful program on new sulphur -containing compounds such as thioacetaldehyde (see image above) and other very interesting species. The synergistic technique which we used is described in the introduction to this page and an overview of these species such as thioaldehydes, thioketones seleno analogues and thioborines is summarised here Tilden Lecture Thio Seleno Section
The ramifications of the results on new molecules are discussed here Tilden Lecture Discussion Section
It is a great pleasure to acknowledge the hard work of my co-workers in this research: Anthony Alexander, James Burckett-St. Laurent, Allan Careless, Terry Cooper, Krini Georgiou, Marcus Durrant, Mike Hutchinson, Mike King, Colin Kirby, Barry Landsberg, Don McNaughton, Mike Maier, Osamu Ohashi, Keiichi Ohno, Nigel Simmons, Roger Suffolk, and Nick Westwood. I should also like to acknowledge the debt I owe to my Sussex colleagues, John Nixon with whom the phosphorus work has been carried out and David Walton with whom the poly-ynes were studied. In addition the help and encouragement of Michael Lappert, Bill McCrea, John Murrell, and Jim Watson have been consistent and invaluable. Finally, it has been a pleasure to collaborate with Takeshi Oka, Lorne Avery, Norm Broten, and John MacLeod in the radioastronomical work.