Examining isotope effects in ion–molecule reactions

Description

Reactions between ions and neutral molecules are known to be important in low-temperature environments such as the outer atmosphere and the interstellar medium. Accurate information on the properties of these ion–molecule reactions is therefore critical for the development of robust models of gas-phase atmospheric and interstellar chemistry. Yet there is a lack of experimental data on ion–molecule reaction systems under low-temperature conditions. It is exceedingly challenging to undertake such measurements; only a handful of experimental techniques have successfully established accurate rate coefficients and branching ratios at temperatures below 298 K (<25°C). We have developed an innovative approach for monitoring ion–molecule reactions under highly controlled conditions, using a combination of ion trapping and laser cooling-based methods coupled with sensitive detection techniques. High-level theoretical work has been conducted alongside the experimental measurements, to help us interpret the results and understand the reaction mechanism.

Previous studies have revealed the presence of inverse kinetic isotope effects—where deuterated molecules react faster than the hydrogenated species—in certain charge transfer reactions. In this project, we seek to use a combination of experimental and theoretical methods to establish how widespread inverse kinetic isotope effects might be, and to explain the mechanism(s) responsible for this behaviour in ion–molecule reaction systems.

Experiments will involve the use of a linear Paul ion trap and laser cooling techniques, for the formation of cold ionic targets, alongside molecular beam generation and laser manipulation, for the preparation of neutral reactants. Reactions will be monitored using imaging and time-of-flight mass spectrometry detection techniques. Experimental work will be complemented by detailed computational work, including capture theory modelling and high-level quantum chemistry and dynamics calculations. This combination of experimental and theoretical work will enable us to validate (or challenge) existing models of ion–molecule chemical reactivity.

Candidates should have at least a 2.1 undergraduate degree (ideally a four-year integrated Master’s degree, or a three-year Bachelor’s degree with a stand-alone Master’s qualification) in Chemistry, Physics or a related field. The successful applicant will have the opportunity to work closely with our diverse team – including physicists, chemists, and computer scientists. Expert mentoring and training will be provided by members of the supervisory team: Dr Brianna Heazlewood (Liverpool), Dr Jérôme Loreau (KU Leuven), and Professor Tim Softley (Birmingham). Further information on our research, alongside a list of publications, can be found at:

https://www.liverpool.ac.uk/physics/research/heazlewood-group/research/ 

https://www.liverpool.ac.uk/study/postgraduate-research/how-to-apply/.

Please ensure you include the project title in your online application and quote reference PPPR042.