Theoretical Investigations of the OH-Initialized Oxidation of 4-Methyl-3-Penten-2-One in the Atmosphere

The present work represents the reaction mechanism and kinetics study of the 4-methyl-3-penten-2-one initiated by OH radicals. The geometries of all stationary points are optimized at the M06-2X/6-311+ +G(d, p) level of theory, and the energy values are refined by making single point energy calculation at the CCSD(T)/6-311++G(d, p) level of theory to construct an energy-level diagram. By employing conventional transition state theory along with a tunneling coefficient, the overall rate constants are calculated in the temperature range of 180-360 K and can be summarized by a modified Arrhenius three-parameter fit expression: k (T) = 6.72 x 10(-20 )x T-2.5 x exp (2056.4/T) cm(3) molecule(-1) s(-1). The rate constant obtained at 298 K is found to be 1.02 x 10(-10) cm(3) molecule(-1) s(-1), which is in good agreement with the experimental data. In the atmosphere, the major oxidation products of the title reaction are acetone, methyl glyoxal, (CH3)(2)COHC(O)H, CO2, and formaldehyde, which are in accordance with experimental detection. The atmospheric lifetime of 4-methyl-3-penten-2-one initiated by OH radicals and the impact of products on tropospheric chemistry have been provided in the paper.