Theoretical study on the HACA chemistry of naphthalenyl radicals and acetylene: The formation of C₁₂H₈, C₁₄H₈, and C₁₄H₁₀ species

Abstract

The hydrogen-abstraction-C 2 H 2-addition (HACA) chemistry of naphthalenyl radicals has been studied extensively, but there is a significant discrepancy in product distributions reported or predicted in literature regarding appearance of C 14 H 8 and C 14 H 10 species. Starting from ab initio calculations, a comprehensive theoretical model describing the HACA chemistry of both 1-and 2naphthalenyl radicals is generated. Pressure-dependent kinetics are considered in the C 12 H 9 , C 14 H 9 , and C 14 H 11 potential energy surfaces including formally direct well-skipping pathways. On the C 12 H 9 PES, reaction pathways were found connecting two entry points: 1-naphthalenyl (1-C 10 H 7) + acetylene (C 2 H 2) and 2-C 10 H 7 + C 2 H 2. A significant amount of acenaphthylene is predicted to be formed from 2-C 10 H 7 + C 2 H 2 , and the appearance of C 14 H 8 isomers is predicted in the model simulation, consistent with high-temperature experimental results from Parker et al. At 1500 K, 1-C 10 H 7 + C 2 H 2 mostly generates acenaphthylene through a formally direct pathway, which predicted selectivity of 66% at 30 Torr and 56% at 300 Torr. The reaction of 2-C 10 H 7 with C 2 H 2 at 1500 K yields 2-ethynylnaphthalene as the most dominant product, followed by acenaphthylene mainly generated via isomerization of 2-C 10 H 7 to 1-C 10 H 7. Both the 1-C 10 H 7 and 2-C 10 H 7 reactions with C 2 H 2 form some C 14 H 8 products, but negligible phenanthrene and anthracene formation is predicted at 1500 K. A rate-of-production analysis reveals that C 14 H 8 formation is strongly affected by the rates of H-abstraction from acenaphthylene, 1-ethynylnaphthalene, and 2ethynylnaphthalene, so the kinetics of these reactions are accurately calculated at the high level G3(MP2,CC)//B3LYP/6-311G ** level of theory. At intermediate temperatures like 800 K, acenaphthylene + H are the leading bimolecular products of 1-C 10 H 7 + C 2 H 2 , and 1-acenaphthenyl radical is the most abundant C 12 H 9 isomer due to its stability. The predicted product distribution of 2-C 10 H 7 + C 2 H 2 at 800 K, in contrast to the results of Parker et al is predicted to consist primarily of species containing three fused benzene rings-for example, 752

C14H10 polycyclic aromatic hydrocarbon formation by acetylene addition to naphthalenyl radicals observed

“…To model experimentally measured reaction rates and product branching ratios, we constructed an elementary-step reaction mechanism containing the reactions involved in the 1naphthalenyl + C 2 H 2 and 2-naphthalenyl + C 2 H 2 systems recently computed at the G3(MP2,CC) level of theory by Chu et al 22 This model chemistry included several new species and pathways in addition to the previously reported potential energy surface from Kislov et al 4 An accurate model for the present experiments required inclusion of several side reactions not discussed by Chu et al or Kislov et al, but fortunately values for many of the rate coefficients of the side reactions (involving e.g. vinyl radicals and iodine atoms) were presented previously in the literature.…”

“…The experimental results are compared with the model prediction up to 10 ms after the photolysis pulse as shown in Figures 2a-2c. Scheme 1 shows a part of the C 12 H 9 potential energy surface from Chu et al 22 The model predicted primary reaction pathway for acetylene addition to 1-naphthalenyl radical is colored red in Scheme 1. Multiple stable products may be formed, including acenaphthylene (ACN), 1-ethynylnaphthalene (ETN-1), and others not included in Scheme 1 but included in the full model (see Ref.…”

“…Considering alternative explanation (i.2) instead: As shown in Figure S19a-b, reducing the rate of the well-skipping reaction (1-naphthalenyl radical + C 2 H 2 → ACN + H) by a factor of 5 significantly improves the agreement between the model prediction and the experimental data at temperatures≤700 K. Reducing the rate of this well-skipping reaction also significantly improves agreement between the model and the experimental data on the branching ratio of m/z = 152 to 153 as shown in Figure 2d-2f, although at 800 K, the model is still over-predicting the branching ratio of m/z = 152 to 153 at longer timescale. A factor of 5 error in the computed rate coefficient is not impossible; it could be due to errors in the calculated reaction barriers or due to the Modified Strong Collision approximation that was used to calculate the pressure-dependent rate coefficients in Chu et al 22 . Previous work by Allen et al 39 showed that this approximation often introduces errors of about a factor of 3 in calculated rate coefficients for chemically-activated reactions, so a factor of 5 error would not be surprising.…”

“…21 Recent theoretical calculations have been reported suggesting that addition of acetylene to 2-naphthalenyl radical at temperatures around 800 K will lead to formation of phenanthrene and anthracene. 22 At around 800 K, the formation and branching of major stable products (including phenanthrene, anthracene, ace-naphthylene, and ethynylnaphthalene) are expected to be highly sensitive to temperature. In order to reconcile previous investigations of the reaction mechanisms for growth from naphthalenyl radicals to three-ring species, direct experimental measurements of the time-resolved product distributions are needed.…”

“…In the current work, we perform direct measurements of the 1-naphthalenyl and 2-naphthalenyl radical reactions with C 2 H 2 to test the validity of a kinetic model recently developed within our group. 22 Vacuum-ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOF-MS) is used to measure the timedependent product formation at 500 to 800 K and 15 to 50 Torr. Products from the first and second C 2 H 2 addition are observed and the results compared with the kinetic model from Chu et al 22 Potential explanations for the observed kinetic behavior are discussed.…”