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Professor Barry Carpenter

My research interests focus on reaction mechanisms.  For many decades, the concept of a reaction mechanism for a thermal reaction has consisted of identifying the stationary points (stable compounds, reactive intermediates, and transition states) on the ground-state potential energy surface, and then enumerating the paths that connect them.  However, in recent years it has become apparent that this is not a sufficient model for a complete mechanistic description.  One problem with it is that the connecting paths can bifurcate in regions that do not correspond to stationary points (see diagram for an example).  When this happens, which we now know it does frequently, none of the existing models for describing reaction kinetics, such as Transition State Theory (TST), are applicable.  The second problem has to do with accounting for the energy released during chemical reactions.  Models such as TST assume that any excess energy released can be treated as instantly redistributed among the vibrational, rotational, and translational degrees of freedom of the molecules involved.  It is now apparent that this assumption is not always valid, and that reactive intermediates in particular can often proceed on to final products at a rate comparable to the rate of redistribution of excess energy.  Again, when this happens TST will fail, and any mechanism based on its assumed validity will be wrong.


  In my work I use molecular dynamics simulations to investigate phenomena of the kind described above.  Often the calculations use direct-dynamics on a potential energy surface described by ab initio or density functional electronic structure theory.  However, I have also recently become interested in the use of empirical valence bond potentials because these allow much faster calculations and hence treatment of larger systems, including, for example, explicit solvent molecules.

Some recent publications on these topics are listed below:

“Prediction of Enhanced Solvent-Induced Enantioselectivity for a Ring Opening with a Bifurcating Reaction Path,” Carpenter, B. K.; Harvey, J. N.; Glowacki, D. R. Phys. Chem. Chem. Phys. in press: DOI: 10.1039/C4CP05078A.

“Nonstatistical Dynamics on the Caldera,” Collins, P.; Kramer, Z. C.; Carpenter, B. K.; Ezra, G. S.; Wiggins, S. J. Chem. Phys. 2014, 141, 034111.

“Effect of a Chiral Electrostatic Cavity on Product Selection in a Reaction with a Bifurcating Reaction Path,” Carpenter, B. K. Theor. Chem. Acc. 2014, 133, 1525.

“Nonstatistical Dynamics on Potentials Exhibiting Reaction Path Bifurcations and Valley-Ridge Inflection Points,” Collins, P.; Carpenter, B. K.; Ezra, G. S.; Wiggins, S. J. Chem. Phys. 2013, 139, 154108.

“Energy Disposition in Reactive Intermediates,” Carpenter, B. K. Chem. Rev. 2013, 113, 7265.