Kinetics of the chemically activated HSO5 radical under atmospheric conditions – a master-equation study

González-García, Núria; Olzmann, Matthias

doi:10.1039/c0cp00284d

Cited by 12 publications

(31 citation statements)

References 54 publications

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“…However, such an approach neglects the fact that the forming reactions (R2a) and (R2b) constantly populate the high‐energy levels of the chemically activated intermediate and in this way compensate for the population depletion caused by the unimolecular reactions. A similar behavior was already discussed in for the intermediate HSO 5 radical in the atmospheric SO 2 oxidation mechanism. That is, even though our study shows that chemical activation does not affect the branching ratios in the considered system, it is clear that a thermal master equation would give wrong results for the rate coefficients of the specific steps.…”

Section: Resultssupporting

confidence: 82%

“…Here, the symbol * indicates that the intermediate C is chemically activated, i.e., obeys a nonthermal energetic distribution, which is influenced by reactions (a)–(c) and collisions with the bath gas. For general aspects of chemical activation, the reader is referred to the monographs and for the influence of consecutive bimolecular steps to .…”

Section: Methodsmentioning

confidence: 99%

“…is most conveniently obtained by directly solving R a F = JN ss for N ss (routines banbks and bandec from ) and subsequent normalization. For more technical details of our approach, see .…”

Section: Methodsmentioning

confidence: 99%

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Consecutive Chemical Activation Steps in the OH‐Initiated Atmospheric Degradation of Isoprene: An Analysis with Coupled Master Equations

Pfeifle

Olzmann

2014

Int J of Chemical Kinetics

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The influence of a two-step chemical activation on 1,5-H and 1,6-H shift reactions of hydroxyl-peroxy radicals formed in the atmospheric photooxidation of isoprene was investigated by means of a master equation analysis. To account for multiple chemical activation processes, three master equations were coupled. The general approach of this coupling is described, and consequences for steady-state regimes are examined. The specific calculations show that chemical activation has no substantial influence on the rate coefficients of the above-mentioned reactions under tropospheric conditions. However, it is demonstrated that high-pressure limits of the thermal rate coefficients instead of the falloff-corrected values have to be used for kinetic modeling. This is a consequence of the continuous population of the high-energy part of the isoprene-OH-O 2 adduct distribution by the forming reactions under steady-state conditions. The rate coefficients of the isomerization reactions at T = 298 K were calculated to be k 3a ∞ = 1.5 × 10 −3 s −1 (1,5-H-shift of the 1,2-isomer) and k 4a ∞ = 6.5 s −1 (1,6-H-shift of the (Z)-1,4-isomer). The calculated value of k 4a ∞ is three orders of magnitude larger than a recently reported experimentally observed rate coefficient for the hydrogen shift reactions of the hydroxyl-peroxy intermediates. It is shown that this discrepancy is in part due to the fact that the experiment does not distinguish between different structural isomers. A comparison of the experimentally determined isotope effect with the calculated value shows a reasonable agreement. C

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Section: Resultssupporting

confidence: 82%

Section: Methodsmentioning

confidence: 99%

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Consecutive Chemical Activation Steps in the OH‐Initiated Atmospheric Degradation of Isoprene: An Analysis with Coupled Master Equations

Pfeifle

Olzmann

2014

Int J of Chemical Kinetics

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“…The sum of states and angular momentum, for both dissociation reactions, were plotted as a function of bond distance and the molecular configuration that minimizes the sum of states was identified. The microcanonical variational transition-state theory (mVTST) rate coefficients were calculated using RRKM theory, [41][42][43][44][45][46][47] and centrifugal corrections were included by averaging k(E, J ) over a thermal distribution of angular momentum J. The highpressure rate coefficients, k N , were obtained by averaging the mVTST coefficients over a Boltzmann distribution.…”

mentioning

confidence: 99%

A theoretical study of three gas-phase reactions involving the production or loss of methane cations

Baptista

Silveira

2014

Phys. Chem. Chem. Phys.

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Hydrocarbon ions are important species in flames, spectroscopy and the interstellar medium. Their importance is reflected in the extensive body of literature on the structure and reactivity of carbocations. However, the geometry, electronic structure and reactivity of carbocations are difficult to assess. This study aims to contribute to the current knowledge of this subject by presenting a quantum mechanics description of methane cation dissociation using multiconfigurational methods. The geometric and electronic parameters of the minimum structure were determined for three main reaction paths: the dissociation CH4(+)→ CH2(+) + H2 and the dissociation-recombination processes CH4(+)↔ CH3(+) + H. The electronic and energetic effects of these reactions were analyzed, and it was found that each reaction path has a strong dependence on the methodology used as well as a strong multiconfigurational character during dissociation. The first doublet excited states are inner-shell excited states and may correspond to the ions that are expected to be formed after electron detachment. The rate coefficient for each reaction path was determined using variational transition state theory and RRKM/master equation calculations. The major dissociation paths, with their rate coefficients at the high-pressure limit, are CH4(+)(X(~)(2)B1) → CH3(+)(A(2)A1') + H((2)S) (k∞(T) = 1.42 × 10(+14) s(-1) exp(-37.12/RT)) and CH4(+)(X(~)(2)B1) → CH2(+)(A(2)A1) + H2((2)Σg(+)) (k∞(T) = 9.18 × 10(+14) s(-1) exp(-55.77/RT)). Our findings help to explain the abundance of ions formed from CH4 in the interstellar medium and to build models of chemical evolution.

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“…The determination of rate constants for chemically activated reactions is slightly more complex than for thermal reactions because two different steady‐state regimes occur. Depending on the timescale of the studied phenomenon and on possible consecutive bimolecular reactions , either an intermediate or a final steady‐state distribution has to be used to obtain the relevant kinetic quantities .…”

Section: The Master Equation and Its Solutionsmentioning

confidence: 99%

Quasi‐Spectral Method for the Solution of the Master Equation for Unimolecular Reaction Systems

Koksharov

Bykov

et al. 2018

Int J of Chemical Kinetics

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Rate constants of elementary reactions involving unimolecular steps can be calculated from molecular data in a most general way by solving appropriate master equations. The conventional numerical solution requires rather a fine discretization applied over a sufficiently large energy range to achieve a reasonable accuracy. This leads to linear but very high‐dimensional systems of differential equations. We propose a quasi‐spectral method that uses Gaussian radial basis functions to establish a low‐dimensional linear model to speed up the numerical integration. The combination with an iterative adaptation provides a further improvement of computational efficiency. The suggested approach is illustrated and exemplified by means of the unimolecular decomposition of 2,3‐dihydro‐2,5‐dimethylfuran‐3‐yl, an intermediate radical occurring in the pyrolysis and oxidation of 2,5‐dimethylfuran. A comparison of the conventional and the proposed method is presented to validate the novel approach and to demonstrate its performance.

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Kinetics of the chemically activated HSO5 radical under atmospheric conditions – a master-equation study

Cited by 12 publications

References 54 publications

Consecutive Chemical Activation Steps in the OH‐Initiated Atmospheric Degradation of Isoprene: An Analysis with Coupled Master Equations

Consecutive Chemical Activation Steps in the OH‐Initiated Atmospheric Degradation of Isoprene: An Analysis with Coupled Master Equations

A theoretical study of three gas-phase reactions involving the production or loss of methane cations

Quasi‐Spectral Method for the Solution of the Master Equation for Unimolecular Reaction Systems

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