Dynamics of Chemical Reactions on Potential Energy Surfaces

Chemical reactions can be conceptualised as motions of atomic nuclei across multidimensional potential energy surfaces (PES), where the topography of valleys, ridges and saddle points governs rates, selectivity and product distributions. Traditional transition state theory locates a dividing surface at the highest energy point along the minimum energy path, but fails to capture dynamical effects arising from the full PES landscape. Trajectory-based approaches, including classical, quasi-classical and ring-polymer molecular dynamics, reveal that under many conditions trajectories depart from the intrinsic reaction coordinate, leading to bifurcations and nonstatistical product outcomes. Such dynamic phenomena arise in cycloadditions, organocatalysed transformations and unimolecular dissociations, where subtle features of the PES—valley–ridge inflections, anharmonic resonances or ambimodal transition states—steer trajectories into competing channels. Understanding these effects is crucial for rational catalyst design, predictive modelling of atmospheric processes and control of stereochemical outcomes. Advances in computational methods, coupled with machine-learning to analyse phase-space information, are now unravelling the intricate interplay between energy landscape and reaction dynamics, enabling more accurate predictions of reaction pathways and branching ratios under realistic conditions.

Research from Nature Portfolio

A study of a model unimolecular dissociation has visualised high-dimensional classical phase space to probe the transition to statistical behaviour. By mapping intersections of multiple anharmonic resonances, researchers identified regions where correlated but chaotic motion delays energy redistribution, a phenomenon termed “stable chaos.” Molecular trajectories can remain trapped near resonance junctions for several picoseconds, thus suppressing statistical dissociation for far longer than predicted by conventional models. This work demonstrates that nonstatistical dynamics on the PES can dominate reaction outcomes and calls for the integration of nonlinear dynamics tools in rate theory.

Dynamics of Chemical Reactions on Potential Energy Surfaces publication trend

The graph below shows the total number of articles in dynamics of chemical reactions on potential energy surfaces across all publications each year (not limited to Nature Index journals).

Technical terms

Potential Energy Surface (PES): A multidimensional hypersurface representing the energy of a molecular system as a function of nuclear coordinates.

Transition State: The highest energy configuration along the minimum energy path that separates reactants and products.

Intrinsic Reaction Coordinate (IRC): The steepest-descent pathway on the PES connecting the transition state to reactant and product minima.

Post-Transition-State Bifurcation: The phenomenon where trajectories diverge into distinct product channels after passing the transition state.

Ambimodal Transition State: A single saddle point on the PES that leads directly to multiple reaction products.

Molecular Dynamics: A computational method that simulates the time-dependent movement of atoms on the PES according to classical or quantum mechanics.

References

1. Computational Design of a Tetrapericyclic Cycloaddition and the Nature of Potential Energy Surfaces with Multiple Bifurcations. Journal of the American Chemical Society (2023).
2. Reaction dynamics as the missing puzzle piece: the origin of selectivity in oxazaborolidinium ion-catalysed reactions. Chemical Science (2023).
3. Temperature effects on the branching dynamics in the model ambimodal (6 + 4)/(4 + 2) intramolecular cycloaddition reaction. Journal of Computational Chemistry (2024).
4. Stable chaos and delayed onset of statisticality in unimolecular dissociation reactions. Communications Chemistry (2020).