Dr. Anthony J. H. M. Meijer

Research Interests

Our research focuses on the theoretical/computational study of chemical reactions. The systems studied vary from small fundamental gas-phase reactions via gas-surface reactions to reactions involving flexible molecules. The results of these calculations are used together with the results of sophisticated experiments to obtain insight into the fundamentals of the reactions involved and to get a fundamental understanding of reaction dynamics. Below are given some projects to illustrate the work.

Gas-surface scattering

We are currently working on the formation of H₂ on graphite. H₂ is the most abundant molecule in interstellar space and it plays an important role in the formation of stars and in interstellar chemistry through reactions with ions and radicals. Moreover, the energetics of the reaction directly influences the thermal balance of the interstellar medium. H₂ is generally supposed to be formed on interstellar dust grains for which the graphite is used as a template. Our calculations complement experiments done in the group of Prof. S. D. Price at UCL and astronomical modelling and observations done in the groups of Prof. D. A. Williams and Dr. J. Rawlings at UCL through the Centre for Cosmic Chemistry and Physics.

Gas-phase reactions

We have done extensive work on the H + O₂ combustion reaction in the past, in particular focusing on the role the total angular momentum in this reaction. This lead to the first-ever rigorous theoretical cross sections, which compared well with experimental data from the Wolfrum group at the University of Heidelberg. We are re-investigating this reaction in collaboration with Dr. M. Hankel of the University of Queensland.

We are also currently applying the methods developed to the photo-dissociation of molecules inside van der Waals complexes, such as Ar-H₂S and Ar-H₂O, where angular momentum effects allow the van der Waals molecule to survive when one of its constituent molecules, such as H₂S, is dissociated. We also have plans to apply the developed methods to the calculation of rates for reactions between radicals at low temperatures, which is important for our understanding of the interstellar medium and our understanding of extraterrestial planets and moons.

Reactions and Structure of conformationally flexible molecules

As molecules become larger, they generally become more flexible. As a consequence the potential energy surface becomes more complicated with many local minima, which may or may not be accessible at thermal energies. Each of these minima will be a distinct structure with e.g. a distinct IR spectrum. We are currently working on methods to allow us to generate many minima, which can then be screened for further investigation. This work ties into a number of collaborations we have, such as with Dr. Mathias Schäffer of the University of Cologne, who studies conformationally flexible molecules in the gas-phase using IRMPD spectroscopy as well as internal collaborations on the structure, reactivity, and properties of organic and organometallic compounds.

Algorithm development for Quantum Dynamics Calculations

Quantum Dynamics calculations are significantly harder than standard electronic structure calculations due e.g. the exponential scaling with respect to the basis set size. We are working on methods that will allow us to solve the time-dependent Schrödinger equation more quickly. In particular, we develop efficient parallel methods to make calculations tractable.

Complete List of Publications

Teaching Section

Physical Chemistry

Undergraduate Courses Taught

• Changes of state (Year 2)
  This segment combines first and second laws of thermodynamics learned in Level 1, so that you can use the Gibbs energy to discuss chemical systems, and the effects of external changes, such as temperature and pressure. This formalism is used to describe physical transformations of pure substances and how such phase changes change due to alteration in the external conditions.
• Quantum Chemistry (Year 2)
  This course covers the basic principles of quantum chemistry with an emphasis on the application of quantum mechanical principles to the electronic structure of molecules.
• Statistical Thermodynamics (Year 3)
  This segment introduces the statistical basis of thermodynamics through development of the concept of the partition function and using it to derive certain properties of ideal monatomic and diatomic gases. It relates both quantum mechanics and spectroscopy to thermodynamic aspects of molecular behaviour. The chief goal of the segment is to establish means whereby Third Law entropies may be calculated and the point of equilibrium established in simple chemical reactions.
• Chemistry in Space (Year 4)
  This course expands on level 3 courses in Physical Chemistry and apply concepts learned therein to the chemistry of compounds in space in general and the interstellar medium in particular.

Tutorial & Workshop Support

• First Year General Tutorials.
• Second Year Physical Chemistry Tutorials.
• Third Year Workshops (Statistical Thermodynamics).
• Third Year Literature Review.
• Fourth Year Workshops (Chemistry in Space).

Laboratory Teaching

• Third Year Advanced Physical Chemistry
• Fourth Year Research Project