Experimental rate coefficient for the reaction of OH radical with (z)-3-hexene at 298 K

THAÍS DA SILVA BARBOSA, SILVINA ANAHÍ PEIRONE, JUAN PABLO ARANGUREN ABRATE, JAVIER BARRERA, SILVIA LANE, GRACIELA ARBILLA DE KLACHQUIN, GLAUCO FAVILLA BAUERFELDT

Conferencia; 13th. IGAC Science Conference and 13th. Quadrennial iCACGP Symposium on Atmospheric Chemistry; 2014

The volatile organic compounds (VOCs) are emitted into the troposphere by both biogenic and anthropogenic sources, playing an important role in atmospheric chemistry. VOCs reactions lead to a complex series of chemical and physical transformations which result in the formation of ozone and oxygenated compounds. It is now well recognized that a wide variety of volatile non-methane organic compounds are emitted into the atmosphere from vegetation, mainly by forests (Guenther et al., 2000). Hexenol and other unsaturated alcohols are mainly emitted by vegetation. Other unsaturated compounds are of anthropogenic origin, such as hexenes. These compounds are used in the production of polymers. The main goal of this work was the study of OH radical + (Z)-3-hexene reaction for a further comparison with its alcohol homologue.The kinetics of the reaction at 298 K and atmospheric pressure was investigated using the relative rate method. The experimental set-up at INFIQC (Argentine) consisted of an 80 L Teflon bag located in a wooden box with the internal walls covered with aluminum foil, and operated at atmospheric pressure and 298K. OH radicals were produced by the photolysis of H2O2 at 254 nm using six germicide lamps. The mixtures of (Z)-3-hexene and reference compounds with H2O2 were stable in the dark when left in the chamber for about 2 h. Moreover, no photolysis of both (Z)-3-hexene and or references was observed. Photolysis was carried out in steps of 2 min, and the total time of photolysis varied from 2 to 12 min. Periodically, gas samples were removed from the Teflon bag using calibrated gas syringes and analyzed using the GC-FID. Relative rate coefficients were determined by comparing the rate coefficients for the reaction of OH radicals with the target compound to that with three reference compounds (cyclohexene, 2-buten-1-ol and allyl ether). The mean value for the second-order rate coefficient was a (0,6±0,1) x 10-10 cm3 molécule-1 s-1 in good agreement with the previous reported value (Grosjean and Williams II, 1992).