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NAME: Natalie Elkins Click here to visit Natalie's website PROJECT TITLE: Ab initio investigation of pre-reactive complexes of hydroxyl radical The hydroxyl (•OH) radical is the principal reactive species in the Earth’s atmosphere. The rate-limiting step of removal of organic species, both natural (such as methane or terpenes) and man-made (such as carbon monoxide or acetone), from the atmosphere is the initial reaction with the •OH radical. This can proceed via two distinct mechanisms: either by hydrogen abstraction, or by addition of •OH to a multiple bond, as in case of carbon monoxide, ethylene, and acetylene. The resulting free radical readily reacts with oxygen and other chemical species in the air in a cascade of reactions ultimately resulting in carbon dioxide and water as final products. For this reason, reactions of hydroxyl radical have been of great interest in studies of chemistry of smog formation and dissipation, greenhouse gases (methane has much higher greenhouse potential than carbon dioxide) and oxidative polymer degradation. Van der Waals (vdW) complexes in the entrance channels of chemical reactions play an important role in chemical reactivity. The long-range intermolecular forces can affect the rates of chemical reactions and/or the ratios of possible products due to pre-orientation of the reactants and cage effects. These effects have been observed experimentally; yet surprisingly little is known about the complexes themselves. We are calculating potential energy surfaces (PESs) of the HO…H2, HO…CO, HO…CH4, HO…C2H2, and HO…C2H4 complexes that serve as the simplest models of various reaction mechanisms. During the Summer of 2009 we plan (i) to obtain benchmark three-dimensional Potential Energy Surfaces (PESs) for the above complexes by extrapolating to complete basis set limit; (ii) investigate the performance of various traditional as well as cutting-edge approaches for calculation of parts of PES that lack a plane of symmetry and the region around transition state; and (iii) model thus obtained surface by analytical function with physical meaning (this is an essential step for future use in modelling dynamics of these systems).
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