laser probes of chemical reactions
The concept that distinguishes chemistry from other sciences is to learn about, understand and then predict and control how one set of connected atoms (a molecule) evolves into another. Whether the simple bond cleavage of a diatomic molecule, or the complexity a biological reaction, the identification of key intermediates and transition state structures defines the current paradigm of the chemical reaction.
Weird Chemistry: Reactions that just don’t go where they should (with Dr Jordan)
Since the 1930’s, the concept of a transition state (TS) has formed the bedrock of chemical reaction theory. In 2004, a mechanism was published concerning the very simple photodissociation of H2CO that seemed not to involve a TS; there was no defined structure through which the reaction passed. Very shortly afterwards we published the second example of this “roaming” reaction in the photodissociation of CH3CHO. Two fragments of acetaldehyde, CH3 and HCO almost separate, but are trapped in their mutual van der Waals well. Here they orbit each other and produce different chemical products. This “roaming” pathway was 10× more efficient that the TS pathway. In 2011, an Honours student in our lab discovered that there are not one, but two different roaming mechanisms in CH3CHO and that the conventional TS mechanism (written about for several decades) is actually unimportant.
There are two projects on offer for 2013:-
- In 2012 we published a paper in Science hypothesizing a new chemical mechanism (phototautomerisation) that is predicted to explain the origin of 30 Mtonnes of organic acids that have been measured but not explained in the atmosphere. This project is to find experimental evidence of this mechanism.
- The atmosphere is full of carbonyl compounds, yet their photochemistry is not very well known nor understood. In this project you will investigate, experimentally and theoretically, the different photochemical pathways of aldehydes, including the wavelength and pressure dependence of the chemistry. Both projects will use state-of-the-art laser systems, and unique spectrometers, manufactured specially for our laboratory. You will use sophisticated theory to aid understanding of the data, and to predict the outcome of other reactions.
Laser Probes of Radical Intermediates in Combustion (with A/Prof Tim Schmidt)
Free radicals are key intermediates in all complex chemical reactions. Over the past 15 years, we have been in the forefront of isolating radicals in a vacuum, where they cannot further react. Over the past 5 years, we have developed new laser-based spectroscopic techniques and have discovered many new radicals. In 2011/2, we started to explore oxygenated radicals, which are crucial to all combustion and atmospheric processes. OH attack on aromatics has been attributed in hundreds of papers as the only reaction of importance in the removal of aromatics from the atmosphere. However, the reaction product (OH adducted to the benzene ring), has been reported only 6 times –all theoretical. In 2011, an Honours student in our lab measured the first spectrum of this radical thereby proving its existence and allowing for it to be characterised.
The project on offer for 2013 is to continue to search for oxygen-containing radicals that are supposedly crucial in the atmosphere and combustion, but have not yet been observed. One candidate is to search for the OH adduct to isoprene. Isoprene is a volatile oil, emitted by many plants. It is the largest volume organic compound emitted to the atmosphere – 500 million tonnes per annum. Reaction with OH is the most likely decomposition pathway and we will seek the crucial radicals involved in this chemistry.
Chemistry Education (with A/Prof Manju Sharma, School of Physics)
I have a long-standing interest in how students learn in the laboratory and have managed a national program on laboratory education for 10 years. There are a variety of Honours projects on offer, including both higher education (university) and secondary education sectors.
For further information, please contact:
School of Chemistry
University of Sydney NSW 2006
Phone: +61 2 9351 2756