Many chemical processes can ultimately be understood in terms of the interactions of only a few particles. Our group studies few-body phenomena relevant to chemistry, with a particular emphasis on three-body recombination and termolecular reactions. Our approach combines theory and numerical simulation.
Termolecular Reactions
For over a century, it has been assumed that termolecular reactions occur in a sequential manner: two reactants first collide and form an intermediate complex, which is subsequently stabilized or transformed through interaction with a third particle. Our group explores a different possibility: direct three-body reactions, in which all three reactants participate simultaneously in the collision dynamics leading to product formation. To study these processes, we have developed classical trajectory methods formulated in hyperspherical coordinates, together with adiabatic-channel approaches that provide an intuitive description of three-body dynamics. These tools allow us to investigate the mechanisms and rates of termolecular reactions and to determine when direct three-body processes can compete with, or even dominate over, conventional sequential pathways.
Buffer Gas Chemistry
Buffer gas chemistry explores how chemical reactions can be used inside a cryogenic buffer gas cell to selectively produce cold molecules, enhancing the yield of a desired species while suppressing unwanted byproducts. Our group has pioneered chemistry-based routes for producing cold molecules in buffer gas cells. Instead of relying exclusively on direct laser ablation of a solid target containing the molecule of interest, we use chemical reactions occurring inside the cell to form the desired molecular product. This approach turns the buffer gas cell into more than a cooling environment—it becomes a controlled chemical reactor for producing cold molecules. By understanding and manipulating reaction pathways, kinetics, and
collisional processes, we aim to increase molecular yields and expand the range of species that can be produced for experiments in cold and ultracold molecular science.
The Sulfur Cycle
Sulfur chemistry plays an important role in determining the composition and evolution of planetary and exoplanetary atmospheres. However, many of the elementary reactions involving sulfur-containing species remain poorly characterized, introducing uncertainties into atmospheric models. Our group investigates key sulfur reactions for which reliable reaction mechanisms and rate coefficients are still needed. We begin by using quantum chemistry calculations to construct the underlying potential energy surfaces and then study the resulting reaction dynamics. We are particularly interested in termolecular sulfur chemistry, where our classical trajectory methods in hyperspherical coordinates allow us to explore three-body reaction mechanisms and provide microscopic information that can ultimately be incorporated into models of planetary and exoplanetary atmospheres.
Nucleation: From Collisions to Matter
One may inquire, how do individual molecules come together to form the first stable clusters of a new phase? We approach this fundamental question by viewing gas-phase nucleation from a reaction-dynamics perspective. We describe nucleation as a network of elementary association (termolecular) and dissociation processes (bimolecular). From this perspective, nucleation emerges naturally from a reaction network connecting individual molecules to increasingly large clusters. This microscopic picture allows us to connect molecular interactions and few-body collision dynamics directly with macroscopic quantities such as nucleation rates. As the density increases, however, isolated few-body collisions no longer provide a complete description. Many-body and dense-gas effects become increasingly important, and we complement our reaction-dynamics approach with molecular dynamics simulations to investigate nucleation under these conditions.
