David M. Bartels

David M. Bartels

Hope College, Holland, Michigan, B.A. (1977)
Northwestern University, Evanston, Illinois, Ph.D. (1982)

Phone: (574) 631-5561
Email: bartels.5@nd.edu
Office: 203D Radiation Research Building

Fast Kinetics of Radiation-Initiated Chemistry


Scientific Interests

Fast Kinetics of Free Radical Reactions

Rate constants for radiation-induced radical reactions in solution.

Reaction Rates of the Hydrated Electron

Measuring and modeling hydrated electron reaction rates.

Solvent Effects on Reaction Rates in Supercritical Water

Reaction rates for radiolytic transients under extreme conditions.

Radiation-Enhanced Corrosion

Quantifying radiation-enhanced corrosion and exploring mitigation strategies

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Recent Accomplishments 

Hydrated electron structure

Bartel S Art Jan 2019

Solvation "structure" of the hydrated electron has been a subject of hot debate since its discovery in 1962.  The most recent controversy has raged over whether the electron primarily exists in a "cavity" between water molecules, or is solvated by a densified patch of solvent.  In collaboration with Kumar and Sevilla of Oakland University, we recently found that virtually all of the hydrated electron properties could be reproduced using a minimal four-water ab initio model in dielectric continuum, where one bond of each water molecule points toward a central void.  Given the large spin density on the water molecules, the ab initio model is much better described as a "multimer solvent anion" than as an "electron in a solvent cavity".

Hyperfine coupling of the hydrogen atom in water

High precision measurement of hydrogen atom EPR splitting in water shows its hyperfine coupling is about one ppt below the vacuum hfc, and moves further away from the vacuum value at higher temperature.  Eventually at ca. 250°C, the hfc turns around and heads back toward the vacuum value.  A simple model explains this in terms of the frequency of collisions between H and the water molecules.  However, very high level ab initio calculations predict the opposite behavior, that the hfc in water should be higher than the vacuum value.  Experiment and theory seem to be at an impasse on this supposedly simple problem.

Small free radical recombinations in high temperature water

Near room temperature, recombination of small free radicals like H and OH are nearly diffusion limited in aqueous solution, i.e. once they meet their reaction is certain. We have been surprised to learn that above about 200°C, "barrierless" reactions involving H and OH are no longer limited by diffusion. Diffusion becomes so fast that the solvent "caging effect" fails to average over all possible angles of approach, and the reaction rate is limited by a "steric effect."  We showed that for recombination of hydroxymethyl radicals, the diffusion limit is not even reached at room temperature. The great surprise has been that the rates measured in water, where hydrogen bonding was assumed to be important, are identical to the "high pressure limit" rate in the gas phase. Water is "merely" a very effective third body for energy transfer.

Modeling of nuclear reactor chemistry

Surprisingly, the radiation chemistry occurring in nuclear power reactors has not been successfully modeled until recently. A review of all reaction rates and radiolysis product yields was prepared in collaboration with John Elliot of Atomic Energy of Canada in 2008, which included all of the new high temperature information generated in our laboratories. Simulation of the "Critical Hydrogen Concentration" or excess added hydrogen needed to suppress radiolysis in the reactor cores was still not successful. Additional experiment and modeling shows that radiolysis yields due to neutron radiation has not been correctly measured in laboratory experiments. This key missing information is now a primary target of research.

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Selected Publications

Sargent, L.; M. Sterniczuk and D.M. Bartels. “Reaction rate of H atoms with N2O in hot water” Radiat. Phys. Chem. 135 (2017): 18-22. link

Walker, J.A., S.P. Mezyk, E. Roduner, and D.M. Bartels. “Isotope Dependence and Quantum Effects on Atomic Hydrogen Diffusion in Liquid Water.” J. Phys. Chem. B 120 (2016): 1771-9. link

Sterniczuk, M., and D.M. Bartels. “Source of Molecular Hydrogen in High-Temperature Water Radiolysis.” J. Phys. Chem. A 120 (2016): 200-9. link

Kumar, A., J.A. Walker, D.M. Bartels, and M.D. Sevilla. “A Simple ab Initio Model for the Hydrated Electron that Matches Experiment.” J. Phys. Chem. A 119 (2015): 9148-59. link

Kanjana, K., J.A. Walker, D.M. Bartels. “Hydroxymethyl Radical Self-Recombination in High-Temperature Water.” J. Phys. Chem. A 119 (2015): 1830-7. link

Nuzhdin, K., D.M. Bartels. “Hyperfine Coupling of the Hydrogen Atom in High Temperature Water.” J. Chem. Phys. 138 (2013): 124503. link

 

 

 

 

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