PAH Formation under Single Collision Conditions: Reaction of Phenyl Radical and 1,3-Butadiene to Form 1,4-Dihydronaphthalene

Abstract

The crossed beam reactions of the phenyl radical (C(6)H(5), X(2)A(1)) with 1,3-butadiene (C(4)H(6), X(1)A(g)) and D6-1,3-butadiene (C(4)D(6), X(1)A(g)) as well as of the D5-phenyl radical (C(6)D(5), X(2)A(1)) with 2,3-D2-1,3-butadiene and 1,1,4,4-D4-1,3-butadiene were carried out under single collision conditions at collision energies of about 55 kJ mol(-1). Experimentally, the bicyclic 1,4-dihydronaphthalene molecule was identified as a major product of this reaction (58 ± 15%) with the 1-phenyl-1,3-butadiene contributing 34 ± 10%. The reaction is initiated by a barrierless addition of the phenyl radical to the terminal carbon atom of the 1,3-butadiene (C1/C4) to form a bound intermediate; the latter underwent hydrogen elimination from the terminal CH(2) group of the 1,3-butadiene molecule leading to 1-phenyl-trans-1,3-butadiene through a submerged barrier. The dominant product, 1,4-dihydronaphthalene, is formed via an isomerization of the adduct by ring closure and emission of the hydrogen atom from the phenyl moiety at the bridging carbon atom through a tight exit transition state located about 31 kJ mol(-1) above the separated products. The hydrogen atom was found to leave the decomposing complex almost parallel to the total angular momentum vector and perpendicularly to the rotation plane of the decomposing intermediate. The defacto barrierless formation of the 1,4-dihydronaphthalene molecule involving a single collision between a phenyl radical and 1,3-butadiene represents an important step in the formation of polycyclic aromatic hydrocarbons (PAHs) and their partially hydrogenated counterparts in combustion and interstellar chemistry.

A crossed molecular beam and ab initio study on the formation of 5- and 6-methyl-1,4-dihydronaphthalene (C11H12) via the reaction of meta-tolyl (C7H7) with 1,3-butadiene (C4H6)

“…Note that we considered a broad variety of reaction channels analogous to those studied earlier for the reaction of the phenyl radical with 1,3-butadiene, 31 but in this discussion we concentrate only on the most important channels (Fig. We are now considering the energetics of the reaction and attempt to identify the product isomer by comparing the experimentally determined reaction energy of 121 AE 34 kJ mol À1 with theoretically calculated energies for distinct C 11 H 12 isomers.…”

“…24 Aromatic radicals like the phenyl radical (C 6 H 5 ) are thought to be key intermediates in PAH formation. [26][27][28] The formation of prototypical two ring PAHs indene (C 9 H 8 ), 29 naphthalene (C 10 H 8 ), 30 and 1,4-dihydronaphthalene (C 10 H 10 ) 31 have recently been demonstrated to occur in reactions of the phenyl radical with allene/methylacetylene (H 2 CCCH 2 /CH 3 CCH), vinylacetylene (CH 2 CHCCH), and 1,3-butadiene (H 2 CCHCHCH 2 ), respectively, under single collision conditions. [26][27][28] The formation of prototypical two ring PAHs indene (C 9 H 8 ), 29 naphthalene (C 10 H 8 ), 30 and 1,4-dihydronaphthalene (C 10 H 10 ) 31 have recently been demonstrated to occur in reactions of the phenyl radical with allene/methylacetylene (H 2 CCCH 2 /CH 3 CCH), vinylacetylene (CH 2 CHCCH), and 1,3-butadiene (H 2 CCHCHCH 2 ), respectively, under single collision conditions.…”

“…25 Their reactions with small, unsaturated hydrocarbons (C3 and C4) have been proposed to provide the primary link between the first aromatic ring and multiple ring species. 30,31 On the other hand, the mechanisms to methyl substituted PAHs have not received an equal level of attention, although they appear to be produced in equal quantities in combustion environments and could be responsible for key features in the UIEs and DIBs. The reaction leading to indene has an entrance barrier of about 14 kJ mol À1 , while the reactions of phenyl radicals with vinylacetylene and 1,3-butadiene involve submerged barriers implying naphthalene (C 10 H 8 ) and 1,4-dihydro-naphthalene (C 10 H 10 ) can be formed in low temperature interstellar environments, as low as 10 K, such as in molecular clouds.…”

Formation of bicyclic polycyclic aromatic hydrocarbons (PAHs) from the reaction of a phenyl radical with cis-3-penten-1-yne

“…[11][12][13] And, isoprene (C 5 H 8 ), the methyl-substituted 1,3-butadiene, was found to react with phenyl radical barrier-lessly. 26,41 However, Hansen et al 42 identied the isomers of linear C 5 chemicals, and found that cis-3-penten-1-yne (CH^C-CH]CH-CH 3 ) was the most stable linear C 5 H 6 , and CH^C-CH]CH-CH 2 radical the most stable linear C 5 H 5 radical. Structurally, CH^C-CH]CH-CH 3 is the methylsubstituted product of vinylacetylene (CHCCHCH 2 ), which can form naphthalene via the bimolecular reactions with para-tolyl and phenyl radicals without entrance barriers under single collision conditions.…”

Kinetic modeling study of benzene and PAH formation in laminar methane flames

“…There are no comprehensive kinetic modeling investigations on laminar methane flames, including the validations under the premixed, counter flow and coflow diffusion flame conditions. Based on the recent progress in the combustion kinetics of methane [36], and the efforts on the combustion of benzene [49][50][51][52], toluene [43,[53][54][55] and naphthalene [44,46,[56][57][58][59], a detailed kinetic model was developed for the combustion and PAH formation in laminar methane flames. This model was validated against the experimental data of laminar flames in various previous investigations, including the premixed flames [22][23][24], and the counter flow flames [60], whose operative conditions are reported in Table 1.…”