AB INITIO THEORETICAL STUDY OF THE HO + CO → CO2 + H ENVIRONMENTAL CHEMICAL REACTION

Abstract

Atmospheric temperature affects both the absorption spectrum and the con- centration of atmospheric  gases. Gases with larger abundances and stronger absorption band intensities in the infrared region have a greater influence on the greenhouse effect. The purpose of this work is to provide an ab initio theoretical conformational model of the reaction between the OH radical and CO, which is used to model common environmental reactions. The geometric optimization of the studied structures was performed using Hartree-Fock (HF) methodology, B3LYP (Becke, three-parameter, Lee-Yang-Par) and the Moller- Plesset perturbation theory to the 2nd order (MP2), using the 6-311++G** basis set and Gaussian 09W software for all calculations. Three stationary structures and six transition structures were found and were characterized by their normal modes of vibration. Using this methodology,  we discovered two possible paths for the studied reaction, which were characterized by their potential energy hypersurface. These paths are the geometric  isomers cis and trans HOCO radicals that yield a ∆H for the general reaction of -34.51 kcal/mol.  According to the Hammond postulate, which relates the similar- ity in transition states with the reactants or products, the transition states participating in the studied reaction have a similar energetic character to the reactants, which is generally observed in exothermic reactions.