Mechanism and Kinetics of the Reaction of OH Radicals with Glyoxal and Methylglyoxal: A Quantum Chemistry+CVT/SCT Approach

• Published in: Chemphyschem 2004-09, Vol.5 (9), p.1379-1388
• Main Authors: Galano, Annia, Alvarez-Idaboy, J. Raúl, Ruiz-Santoyo, Ma. Esther, Vivier-Bunge, Annik
• Format: Article
• Language: English
• Subjects: aldehydes; Applied sciences; Arrhenius parameters; Atmospheric pollution; canonical variational theory; Crystallography, X-Ray; Exact sciences and technology; Glyoxal - chemistry; Hydroxyl Radical - chemistry; Kinetics; Models, Chemical; Models, Molecular; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Pyruvaldehyde - chemistry; Quantum Theory; radical ions; reaction mechanisms; Temperature; Thermodynamics
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200400127

A theoretical study of the mechanism and kinetics of the OH hydrogen ion from glyoxal and methylglyoxal is presented. Optimum geometries, frequencies, and gradients have been computed at the BHandHLYP/6–311++G(d,p) level of theory for all the stationary points, as well as for 12 additional points along the minimum energy path (MEP). Energies were obtained by single‐point calculations at the above geometries using CCSD(T)/6–311++G(d,p) to produce the potential energy surface. The rate coefficients were calculated for the temperature range 200–500 K by using canonical variational theory (CVT) with small‐curvature tunneling (SCT) corrections. Our analysis suggests a stepwise mechanism, which involves the formation of a reactant complex. The overall agreement between the calculated and experimental kinetic data is very good. This agreement supports the reliability of the Arrhenius parameters of the glyoxal + OH reaction that are proposed in this work for the first time. The Arrhenius expressions that best describe the studied reactions are k1=(9.63±0.23)×10−13 exp[(517±7)/T] and k2=(3.93±0.11)×10−13 exp[(1060±8)/T] cm3 molecule−1 s−1 for glyoxal and methylglyoxal, respectively. Working for the troposphere: The OH ion reactions from glyoxal and methylglyoxal were modeled according to a complex mechanism that involves the formation of a reactant complex (represented here by RC‐G). The results obtained in this work may help to improve air‐quality models.