The reactions of O( 3P) atoms with aromatic hydrocarbons with unsaturated side chains

Abstract

For the understanding of combustion chemistry and soot formation, it is necessary to know the elementary reactions of aromatic hydrocarbons with unsaturated side chains. This paper deals with present kinetic data and results of product analyses of the reactions of oxygen atoms (O( 3 P)), with (1) 2-propenylbenzene (C 6 H 5 -CH 2 -CH=CH 2 ), (2) 2-propynylbenzene (C 6 H 5 -CH 2 -C≡-C-H), (3) cis-stilbene (C 6 H 5 -CH=CH-C 6 H 5 ) and (4) biphenylacetylene (C 6 H 5 -C≡C-C 6 H 5 ). A continuous flow reactor was used with molecular-beam sampling and mass spectrometric deterction. Oxygen atoms were produced by chopped microwave discharges in a mixture of oxygen and helium as carrier gas; in all cases, the reactions took place under pseudo-first-order conditions with an excess of oxygen atoms. The kinetic measurements were carried out in the temperature range of 298–873 K. The kinetic investigations show that, for all four compounds, two main reaction channels have to be considered: the phenyl group and the side chain. The electrophilic addition of O( 3 P) to the aromatic ring of these compounds is important at high temperatures (above 500 K). The following Arrhenius expressions were obtained and as shown in Figure 1. ( k=k aromatic + k side chain in cm 3 /mol×s): k 1 ( T ) = ( 1.7 ± 0.5 ) 10 13 × exp ⁡ ( − ( 2000 ± 200 ) K T ) + ( 2.3 ± 0.7 ) 10 12 × exp ⁡ ( − ( 250 ± 30 ) K T ) k 2 ( T ) = ( 1.7 ± 0.5 ) 10 13 × exp ⁡ ( − ( 2400 ± 240 ) K T ) + ( 6.4 ± 1.2 ) 10 12 × exp ⁡ ( − ( 810 ± 50 ) K T ) k 3 ( T ) = ( 1.2 ± 0.5 ) 10 13 × exp ⁡ ( − ( 1400 ± 150 ) K T ) + ( 5.0 ± 1.0 ) 10 10 × exp ⁡ ( − − ( 430 ± 40 ) K T ) k 4 ( T ) = ( 9.5 ± 2.5 ) 10 12 × exp ⁡ ( − ( 2200 ± 220 ) K T ) + ( 2.5 ± 1.0 ) 10 10 × exp ⁡ ( − ( 50 ± 30 ) K T )