News

New joint experimental-theory paper with USCD experimental positron group: “Positron annihilation and binding in aromatic and other ring molecules”, published in PRA as an Editors Suggestion

Our joint experimental-theory work performed in collaboration with the pioneering UCSD experimental positron group on “Positron binding in aromatic and other ringed molecules” has been published as an Editors’ Suggestion in PRA: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.109.062801

In this work blind comparisons of binding energies calculated with our ab initio many-body theory were made with new measurements by the USCD experimental group, finding good to excellent agreement, and demonstrating the predictive capability of our approach. We elucidated the competition between dipole moment and pi bonds in positron-molecule binding. On the experimental side, many new annihilation spectra and insights were presented.

https://arxiv.org/abs/2312.02779

Our new Phys. Rev. A Letter: How do molecular properties affect positron binding? Positron binding to halogenated hydrocarbons

In groundbreaking new work published as a Phys Rev A Letter, we applied our ab initio many-body theory to study trends in positron binding across molecular families, notably halogenated hydrocarbons. For chlorinated molecules excellent agreement with measurements by the UCSD Surko group are found. Predictions for brominated and fluorinated molecules are presented. Overall, we show that global molecular properties are not universal predictors of positron-molecule binding energies, and we explain the importance of the potential anisotropy and the density of electron states.

J. P. Cassidy, J. Hofierka, B. Cunningham, C. M. Rawlins, C. H. Patterson and D. G. Green, Phys. Rev. A Letter L 109, L040801 (2024) [Open Access]

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.109.L040801

Antimatter-bonded molecules!

Our latest work, on positronically-bonded molecules, has been published in the Journal of Chemical Physics, in the highly-selective 2024 Emerging Investigators Special Collection and as a JCP Featured Article.

Molecules as we typically know them are comprised of two or more atoms glued together by the sharing of electrons. But, in 2019 a South-American research group (Charry, Reyes and Varella) predicted antimatter-bonded molecules, specifically molecules who’s fragments were anions glued together by a positron. We have developed and applied our many-body theory of positron-molecule interactions to describe such positronically-bonded molecules, using it to predict positronically-bonded molecules with molecular fragments, e.g., the binding of two NCO negative ions by a positron.

See J. P. Cassidy, J. Hofierka, B. Cunningham and D. G. Green, J. Chem. Phys. 160, 084304 (2024) [Emerging Investigators Special Collection].

Introducing Dr Hofierka: Jaroslav successfully defends his PhD!

Group PhD student Jaroslav Hofierka successully completed his PhD, titled “Many-body theory of positron-molecule interactions”. Below is a photo of the group with the external examiner Prof Vitali Averbukh (Imperial College London) and our colleague Dr Gleb Gribakin (QUB internal examiner).

Congratulations to Jaroslav! Jaroslav will now take up a postdoc position with the internationally-renowned Heidelberg group of Prof Lorenz Cederbaum. We look forward to the opportunity to collaborate with Jaroslav in the future!

From left to right: Prof Vitali Averbukh (Imperial College London, external examiner), Dr Jaroslav Hofierka (now at Heidelberg University), Dr Gleb Gribakin (QUB internal examiner), Sarah Gregg, Dr Brian Cunningham, Dr Andrew Swann, Jack Cassidy and Dr Dermot Green (supervisor)

Dermot gives Plenary talk at POSMOL, Notre Dame, USA

POSMOL 2023, held in Notre Dame University, South Bend Indiana, USA combined the XXI International Workshop on Low-Energy Positron and Positronium Physics and the XXIII International Symposium on Electron-Molecule Collisions and Swarms.

Dermot gave the EPJD sponsored Plenary talk on his group’s work on “Many-body theory of positron-molecule interactions”.


Group member Dr David Waide successfully defends his PhD viva and graduates!

Our group member Dr David Waide, co-supervised by Dermot and Gleb Gribakin, successfully defended his PhD thesis on “Many-body theory of positron interactions with atoms and atomic clusters”.

Congratulations Dr Waide!

Left: Dr Connor Ballance (internal examiner), Dr David Waide, and Dr Mark Law (University of Aberdeen, external examiner)

Here’s a photo from graduation day, with Dermot

Dr David Waide and one of his PhD supervisors Dr Dermot Green, graduation day for School of Mathematics and Physics at Queen’s University Belfast, 4th July 2023