Rate coefficients for the reaction of OH radicals with cis-3-hexene: an experimental and theorectical study

THAÍS DA SILVA BARBOSA, SILVINA PEIRONE, JAVIER A. BARRERA, JUAN P.A. ABRATE, SILVIA I. LANE, GRACIELA ARBILLA AND GLAUCO FAVILLA BAUERFELDT

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2015 vol. 17 p. 8714 - 8722

1463-9076

The kinetics of the cis-3-hexene + OH reaction were investigated by an experimental relative ratemethod and at the density functional theory level. The experimental set-up consisted of a 200 L Teflonbag, operated at atmospheric pressure and 298 K. OH radicals were produced by the photolysis of H2O2at 254 nm. Relative rate coefficients were determined by comparing the decays of the cis-3-hexene andreference compounds (cyclohexene, 2-buten-1-ol and allyl ether). The mean second-order ratecoefficient value found was (6.27 0.66) 1011 cm3 molecule1 s1, the uncertainty being estimated bypropagation of errors. Theoretical calculations for the addition reaction of OH to cis-3-hexene have alsobeen performed, at the BHandHLYP/aug-cc-pVDZ level, in order to investigate the reaction mechanism,to clarify the experimental observations and to model the reaction kinetics. Different conformations of thereactants, pre-barrier complexes and saddle points were considered in our calculations. The individual ratecoefficients, calculated for each conformer of the reactant, at 298 K, using a microcanonical variationaltransition state method, are 4.19 1011 and 1.23 1010 cm3 molecule1 s1. The global rate coefficientwas estimated from the Boltzmann distribution of the conformers to be 8.10 1011 cm3 molecule1 s1,which is in agreement with the experimental value. Rate coefficients calculated over the temperaturerange from 200?500 K are also given. Our results suggest that the complex mechanism, explicitly consideringdifferent conformations for the stationary points, must be taken into account for a proper descriptionof the reaction kinetics.