Dynamics of molecule-molecule inelastic scattering: Experiment and theory to study correlated rotational excitation in collisions of NO and CO with small molecules


   School of Engineering & Physical Sciences

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  Prof Matthew Costen, Prof K G McKendrick  No more applications being accepted  Funded PhD Project (UK Students Only)

About the Project

This PhD opportunity will be in the Molecular Scattering research group at Heriot-Watt University, Edinburgh.

Please contact Prof Matt Costen ([Email Address Removed]) for further details.

Gas-phase inelastic collisions are of fundamental importance in a wide range of environments, from dense interstellar clouds, through planetary atmospheres to technological plasmas and combustion. Understanding these collisions, and being able to accurately model them, is vital for understanding and predicting the chemistry of these environments. Because of their (relative) simplicity, rotationally inelastic collisions, in which translational and rotational energy are exchanged, have also become test beds for both experiment and theoretical modelling. In the last few years, the forefront of this field, including our own work at Heriot-Watt, has focused on the correlations of rotational excitation in molecule-molecule collisions. This can be expressed as the question ‘If molecule A is formed in state j1, what is the distribution of populated rotational states, j2 for molecule B?’. An associated question is then ‘What is the distribution of scattering angles (the differential cross section) for a specific j1-j2 product pair?’.

Our experiments use state-of-the-art methods, in which the collision partners are first prepared in molecular beams, then are crossed in high vacuum. An additional step of optical-state preparation with an ultraviolet or infra-red laser provides full rotational-quantum-state resolution in one of the colliders. The products of the collision are then probed by resonance-enhanced-multiphoton ionisation, coupled to velocity-map ion-imaging. This provides full rotational-quantum-state resolution in the probed product, and through conservation of energy and momentum also provides the correlation of scattering angle with the internal energy of the unobserved collision partner. Typical systems include NO and CO as the probed species in collisions with other small molecules e.g. N2, CO, O2, CH4, CO2. These experiments proceed hand-in-hand with theory, where ab initio potential-energy surfaces that describe the forces between the collision partners are used in either classical- or quantum-scattering calculations to predict and interpret the experimental results. You will have the opportunity to learn state-of-the-art experimental methods, including using high-vacuum apparatus, multiple laser systems and the associated integrated data acquisition and control, as well as developing expertise in image processing, custom data analysis and classical and quantum scattering methods.

This work is part of a large collaboration, within Heriot-Watt and externally with the University of Oxford, funded through a major EPSRC Programme Grant ‘New Directions in Molecular Scattering’ (https://molecularscattering.com/). There are regular on-line and in-person meetings, and the opportunity for exchange visits to our collaborators in Oxford.

Chemistry (6) Physics (29)

References

T.F.M. Luxford et al. Journal of Physical Chemistry A 127 6251-6266 (2023)
J. G. Leng et al. Physical Chemistry Chemical Physics 24, 6525 (2022)
T. R. Sharples et al. Nature Chemistry 10 1148 (2018)
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 About the Project