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Extreme chemistry around stars and planets: Unravelling the kinetics of astrochemical reactions at very low temperatures

   Faculty of Engineering and Physical Sciences

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  Prof D Heard  Applications accepted all year round  Funded PhD Project (Students Worldwide)

About the Project

More than 200 molecules have been discovered in interstellar space using modern astronomical telescopes, including complex organic molecules containing a wide range of chemical functional groups. A major open question in astrochemistry concerns the mechanisms for the formation and subsequent fate of these complex species, for example organic molecules containing peptide groups which are considered the building blocks of larger pre-biotic molecules essential for life. At present the networks (mechanisms) used by astrochemists to model abundances of these molecules contains very large gaps in the knowledge of the kinetics of these reactions. At Leeds we have discovered that reactions between two neutral species in the gas-phase play key roles in the astrochemistry of low temperature environments such as the interstellar medium (ISM) and dense molecular clouds of star forming regions, despite the presence of a significant activation barrier to reaction. These reactions proceed via the formation of a weakly-bound complex followed by quantum mechanical tunnelling. In this project, you will explore the chemical mechanisms of key gas-phase astrochemical reactions using both experimental and computational methods. The experimental part of the project involves using a pulsed Laval nozzle apparatus using laser flash-photolysis combined with laser-induced fluorescence (LIF) spectroscopy to study the kinetics of reactions down to temperatures around 25 K, close to those encountered in interstellar space. Rate coefficients, k(T), will be measured for reactions of small free-radicals (O, C and N containing) with organic molecules found in space containing a range of functional groups. In some cases it may also be possible to detect products of these reactions using LIF. To complement the experiments, the potential energy surfaces (PESs) for these reactions will be calculated by ab initio methods utilising the Gaussian suite of computer programmes. The PESs will then be used to compute rate coefficients as a function of temperature and pressure, using the MESMER rate theory software package, which was developed in Leeds. MESMER allows rate coefficients to be calculated outside of achievable experimental conditions, for example down to 10 K, and will enable the calculation of product branching ratios as a function of temperature. Comparison of experiment and theoretical predictions will enable details of the PESs to be optimised. In this project, in collaboration with astrochemical modellers, you will also develop parameterisations for k(T) and use these in astrochemical models to calculate the abundance of complex organic molecules for comparison with telescope observations.

Funding Notes

A highly competitive STFC Doctoral Training Partnership Studentship consisting of the award of fees with a maintenance grant (currently £15,609 for session 2021/22) for 3.5 years. This opportunity is open to all applicants. All candidates will be placed into the STFC Doctoral Training Partnership Studentship Competition and selection is based on academic merit.

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