Energy transfer in intermolecular collisions of polycyclic aromatic hydrocarbons with bath gases He and Ar

Wang, Hongmiao; Wen, Kaicheng; You, Xiaoqing; Mao, Qian; Luo, Kai H.; Pilling, Michael J.; Robertson, Struan H.

doi:10.1063/1.5094104

“…The distributions of for PAH monomers have a long tail toward tens of visited sites indicating that surface diffusion exists in the bimolecular collision to an extent. A larger PAH shows a longer tail, which is consistent with the ability of momentum accommodation [52]. For the quasi-surface models, both of C and H sites are higher than that of monomers on average, suggesting that diffusive scattering dominates the interactions between the incident H and surface atoms.…”

Section: Surface Diffusionsupporting

confidence: 71%

Hydrogen Abstraction/Addition Reactions in Soot Surface Growth

Chu

¹

,

Shi²,

Wang³

et al. 2020

Preprint

0

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<p>The hydrogen abstraction (HB) and addition reactions (HD) by H radicals are examined on a series of polycyclic aromatic hydrocarbon (PAH) monomers and models of quasi-surfaces using quasi-classical trajectory (QCT) method. The QCT results reproduce the rate constants of HB reactions on PAH monomers from density function theory (DFT) in the range of 1500-2700 K. The PAH size has a minor impact on the rates of HB reactions especially at temperatures beyond 2100 K. By contrast, HD reactions have a clear size dependence and a larger PAH yields a higher rate. It is also found that the preferred reaction pathway changing from HB to HD reactions at ~1900 K. The rates of surface HB and HD reactions exceed those in the gas phase by nearly a factor of magnitude. Further analysis on the detailed trajectory of QCT method reveals that about 50% of the surface reactions can be attributed to the events of surface diffusion, which depends on the local energy transfer in the gas-surface interactions. However, this phenomenon is not preferred in PAH monomers as expected. Our finding here highlights the misinterpretation of surface reactions as the product of the first collision between gaseous species and particle surface, and surface diffusion induced reactions should be accounted for in the rates of surface HB and HD reactions. Rate constants of HB and HD reactions on each reactive site (surface zig-zag, surface free-edge and pocket free-edge sites) are calculated by QCT method, which are recommended for the further development of surface chemistry models in soot formation.</p>

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“…The distributions of 𝑁 for PAH monomers have a long tail toward tens of visited sites indicating that surface diffusion exists in the bimolecular collision to an extent. A larger PAH shows a longer tail, which is consistent with the ability of momentum accommodation [52]. For the quasi-surface models, both 𝑁 of C and H sites are higher than that of monomers on average, suggesting that diffusive scattering dominates the interactions between the incident H and surface atoms.…”

Section: Surface Diffusionsupporting

confidence: 71%

Hydrogen Abstraction/Addition Reactions in Soot Surface Growth

Chu

¹

,

Shi²,

Wang³

et al. 2020

Preprint

0

View full text Add to dashboard Cite

<p>The hydrogen abstraction (HB) and addition reactions (HD) by H radicals are examined on a series of polycyclic aromatic hydrocarbon (PAH) monomers and models of quasi-surfaces using quasi-classical trajectory (QCT) method. The QCT results reproduce the rate constants of HB reactions on PAH monomers from density function theory (DFT) in the range of 1500-2700 K. The PAH size has a minor impact on the rates of HB reactions especially at temperatures beyond 2100 K. By contrast, HD reactions have a clear size dependence and a larger PAH yields a higher rate. It is also found that the preferred reaction pathway changing from HB to HD reactions at ~1900 K. The rates of surface HB and HD reactions exceed those in the gas phase by nearly a factor of magnitude. Further analysis on the detailed trajectory of QCT method reveals that about 50% of the surface reactions can be attributed to the events of surface diffusion, which depends on the local energy transfer in the gas-surface interactions. However, this phenomenon is not preferred in PAH monomers as expected. Our finding here highlights the misinterpretation of surface reactions as the product of the first collision between gaseous species and particle surface, and surface diffusion induced reactions should be accounted for in the rates of surface HB and HD reactions. Rate constants of HB and HD reactions on each reactive site (surface zig-zag, surface free-edge and pocket free-edge sites) are calculated by QCT method, which are recommended for the further development of surface chemistry models in soot formation.</p>

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“…Although one can use different theoretical 31 or experimental 32 methods to obtain the energy transfer parameters ⟨Δ E all ⟩ and α, kinetic modelers usually look at the literature for these values of the system under investigation. In many cases, this search fails and then two scenarios are possible.…”

Section: Theoretical and Computational Methodologymentioning

confidence: 99%

Collision Efficiency Parameter Influence on Pressure-Dependent Rate Constant Calculations Using the SS-QRRK Theory

Grajales-González

¹

,

Monge‐Palacios

²

,

Sarathy

³

2020

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The system-specific quantum Rice–Ramsperger–Kassel (SS-QRRK) theory ( J. Am. Chem. Soc. 2016 , 138 , 2690) is suitable to determine rate constants below the high-pressure limit. Its current implementation allows incorporating variational effects, multidimensional tunneling, and multistructural torsional anharmonicity in rate constant calculations. Master equation solvers offer a more rigorous approach to compute pressure-dependent rate constants, but several implementations available in the literature do not incorporate the aforementioned effects. However, the SS-QRRK theory coupled with a formulation of the modified strong collision model underestimates the value of unimolecular pressure-dependent rate constants in the high-temperature regime for reactions involving large molecules. This underestimation is a consequence of the definition for collision efficiency, which is part of the energy transfer model. Selection of the energy transfer model and its parameters constitutes a common issue in pressure-dependent calculations. To overcome this underestimation problem, we evaluated and implemented in a bespoke Python code two alternative definitions for the collision efficiency using the SS-QRRK theory and tested their performance by comparing the pressure-dependent rate constants with the Rice–Ramsperger–Kassel–Marcus/Master Equation (RRKM/ME) results. The modeled systems were the tautomerization of propen-2-ol and the decomposition of 1-propyl, 1-butyl, and 1-pentyl radicals. One of the tested definitions, which Dean et al. explicitly derived ( Z. Phys. Chem. 2000 , 214 , 1533), corrected the underestimation of the pressure-dependent rate constants and, in addition, qualitatively reproduced the trend of RRKM/ME data. Therefore, the used SS-QRRK theory with accurate definitions for the collision efficiency can yield results that are in agreement with those from more sophisticated methodologies such as RRKM/ME.

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Energy transfer in intermolecular collisions of polycyclic aromatic hydrocarbons with bath gases He and Ar

Cited by 13 publications

References 34 publications

Hydrogen Abstraction/Addition Reactions in Soot Surface Growth

Hydrogen Abstraction/Addition Reactions in Soot Surface Growth

Hydrogen Abstraction/Addition Reactions in Soot Surface Growth

Collision Efficiency Parameter Influence on Pressure-Dependent Rate Constant Calculations Using the SS-QRRK Theory

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