Dr. Michael A. Collins
Research School of Chemistry, ANU

Darran Edmundson
ANU Supercomputer Facility Vizlab

Chemical Reaction Dynamics

The theoretical chemical dynamics group at the Research School of Chemistry (RSC) is developing methods to efficiently and very accurately calculate the energy of a molecule as it undergoes a chemical reaction. The calculations are based on so called ab initio quantum chemistry and are therefore "first-principles" results. These are the first methods to provide such highly accurate "energy surfaces" for polyatomic molecules undergoing reaction. The complete mechanism of the reaction can be determined from this energy surface by calculating how all the atoms in the molecule move. The video clips show two examples of the molecular motion, obtained from classical dynamics (Newton's Laws). In collaboration with Assoc. Prof. Dong Hui Zhang and coworkers (National University of Singapore), the essentially exact quantum dynamics of a chemical reaction have been obtained by computer simulation of the Schrodinger equation.
The video clips demonstrate how molecules react by passing through a "transition state"; somewhat simply, we can say that molecules react only if they achieve a shape which is close to the lowest energy shape for which new bonds are formed and old atom-atom bonds are broken. For emphasis, time is slowed in these clips when the molecules are near a transition state.

Collision between a carbon atom (black) and a H3+ molecule to form CH2+ and hydrogen. This reaction lies at the start of a sequence of reactions which form large organic molecules (long chain like molecules containing carbon and hydrogen) in the dark dust clouds between the stars. [2.8 Mb Quicktime]

Two collisions between the hydroxyl radical OH (Oxygen is red) and molecular hydrogen H2. This is an important reaction in the combustion of hydrogen as a fuel. The first collision results in no reaction as the "shape" at impact is not quite close enough to the "transition state", while reaction to form water (H2O) and hydrogen occurs in the second collision. [2.5 Mb Quicktime]

This research appeared on the 3 September 2002 cover of the Proceedings of the National Academy of Sciences of the U.S.A. and was subsequently covered by ABC Television News. A 12 Mb DivX AVI movie of the television report is reproduced here with permission of the ABC.
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