On to other molecules
To date, the team has completed calculations for the reaction pathways of isoprene and two other parent molecules. Dibble states, "We are really near the beginning of this research, and there are so many steps in the reaction sequence just for isoprene. One of the things that hits home is that the experimentalists can see a wide range of reaction products with their techniques, even though they cannot quantify certain other compounds. They also know how much product they cannot account for, which inspires in them a certain caution in the interpretation of their own results.

"With these computations, you ask one question at a time, 'How high is the barrier—how fast is this reaction—for this particular radical?' And get an answer. But you need to be careful to check all the reactions of all the intermediate radicals. Otherwise, you may miss an important reaction and reaction product without having a clue that anything is wrong!"

Although Dibble's team is at an early stage of the modeling process, molecule-by-molecule they are building a valuable knowledge base for the reactions taking place in the atmosphere. The models will demonstrate which reactions dominate the fates of volatile atmospheric molecules and how they affect ozone production. Eventually, that information will help make ozone abatement strategies more efficient.

This research is supported by the Atmospheric Sciences Division of the National Science Foundation's Geophysical Sciences Directorate and by the Petroleum Research Fund of the American Chemical Society.