(376c) Estimating Transition State Geometries for Automatic Reaction Mechanism Generation

Unknown reaction kinetics can be estimated by correlations, or calculated ab initio using quantum chemistry. Software such as Reaction Mechanism Generator (RMG) can automatically build kinetic models containing many thousands of reactions. In RMG, the kinetics are estimated using correlations from analogous reactions. Ab initio calculations could provide more accurate rates than these correlations when kinetic data are sparse. These quantum calculations require tenable estimates of the three-dimensional geometries of the species involved. Recently RMG has been extended to find molecular geometries of reactant and product species, in order to calculate their thermochemistry. The ab initio calculation of reaction rates, however, also requires estimates of the transition state (TS) geometries. We present work towards the automatic generation of these TS geometries in RMG. An initial estimate of the TS geometry is built from the reactant geometries, aligned based on the reactive atoms, and rules specific to each reaction family. This estimated TS geometry will be optimized using a quantum chemistry code, enabling the automatic calculation of reaction kinetics.