faculty

Professor, Atmospheric, Oceanic and Space Sciences and Chemistry
Ph.D., Carnegie-Mellon University
Chemical Kinetics;

Atmospheric Chemistry; Molecular Energy Transfer

Phone: (734)763-6239     
E-mail: jrbarker@umich.edu

Most of the research in our group is motivated by reactions that take place in the Earth and other planetary atmospheres, where the physical conditions cover extreme ranges of pressure and temperature. To model chemical reactions under these conditions is very challenging. Our group is using fundamental principles to understand and to predict the dynamics of complex systems that involve both collisional energy transfer and competing chemical reactions.

Multi-channel, multi-well unimolecular reactions systems are very common and of great practical importance, but are challenging to interpret and predict. For example, when alkyl peroxy free radicals (RO2o) react with nitric oxide in Earth's atmosphere, the highly excited transient alkyl peroxynitrite (RO2NO) initially formed reacts extremely rapidly via two competing channels: reversible isomerization to produce an alkyl nitrate (RONO2) and decomposition to produce an alkoxy radical (ROo) and nitrogen dioxide. Each stage of this process depends on the excitation energy of the reactant species, which is constantly being affected by energy-changing collisions. A full description of such systems requires a multi-channel, multi-well master equation treatment like MultiWell, a computer code developed and supported by our group.

In addition to master equation calculations, our group investigates the dynamics of individual reaction steps by first carrying out electronic structure calculations to construct potential energy surfaces, which we use for quasi-classical trajectory calculations. Topics of particular interest include the dynamics of association reactions, collisional energy transfer, and fast isomerization steps. Our ultimate goal is to develop the expertise needed to predict key reaction rates accurately.

REPRESENTATIVE PUBLICATIONS

1. "Quasi-classical Trajectory Simulations of Intramolecular Vibrational Energy Redistribution in HONO 2 and DONO 2 ", Yong Liu , Lawrence L. Lohr, and John R. Barker, J. Phys. Chem. B, 109 , 8304-8309 (2005).10.1021/jp047436b )

2. "CF 3 CH 3 ? HF + CF 2 CH 2 : A non-RRKM Reaction? ", John R. Barker, Philip J. Stimac, Keith D. King, and David M. Leitner , J. Phys. Chem. A, 110 , 2944-2954 (2006). (DOI: 10.1021/jp054510x)

3. "Quasi-classical Trajectory Simulations of OH(v) + NO 2 ? HONO 2 * ? OH(v') + NO 2 : Capture and Vibrational Deactivation Rate Constants", Yong Liu , Lawrence L. Lohr, and John R. Barker, J. Phys. Chem. A, 110 , 1267-1277 (2006). (DOI: 10.1021/jp053099a)

4. "Intramolecular Vibrational Energy Redistribution Involving the Torsion in CF 3 CH 3 : A Molecular Dynamics Study", Philip J. Stimac and John R. Barker, J. Phys. Chem. A, 110 , 6851-6859 (2006). (DOI: 10.1021/jp0568024)

5. "On modeling the pressure-dependent photoisomerization of trans-stilbene by including slow IVR", Ralph E. Weston, Jr. and John R. Barker, J. Phys. Chem. A, 7888-7897 (2006). (DOI: 10.1021/jp061630b) .