Variational statistical study of the CN+O2 reaction employing ab initio determined properties for the transition state

A combination of ab initio electronic structure and variational statistical calculations are employed in a study of the kinetics of the CN+O2 reaction. Interaction energies for the transition state region of the CN+O2 reaction are evaluated within a multiconfiguration self-consistent field framework. Optimized geometries and force fields are determined for six fixed CO separation distances (RCO) ranging from 1.7 to 3.0 Å and for the NCOO complex. The optimized NCO and COO bending angles are generally near 180° and 115°, respectively. A model analytical potential is fit to the ab initio data. This model potential is then used in variational statistical evaluations of the rate of complex formation employing a bond length reaction coordinate. A comparison between theoretical and experimental results indicates the importance of considering the deviations of the electronic interactions from those predicted by long-range expansions. In particular, variational statistical calculations employing a realistic potential energy surface which fully incorporates the short-range interactions are in quantitative agreement with the experimental data for temperatures ranging from 50 to 3000 K.