Browsing by Author "Xu, S. C."

Now showing 1 - 8 of 8

A computational study on the kinetics and mechanism for the unimolecular decomposition of o-nitrotoluene
(2006-08-24)
Chen, S. C.
;
Xu, S. C.
;
Diau, E.
;
Lin, M. C.
;
應用化學系分子科學碩博班
The kinetics and mechanism for the unimolecular decomposition of o-nitrotoluene (o-CH3C6H4NO2) have been studied computationally at the G2M(RCC, MP2)//B3LYP/6-311G(d, p) level of theory in conjunction with rate constant predictions with RRKM and TST calculations. The results of the calculations reveal 10 decomposition channels for o-nitrotoluene and its six isomeric intermediates, among them four channels give major products: CH3C6H4 + NO2, C6H4C(H) ON (anthranil) + H2O, CH3C6H4O (o-methyl phenoxy) + NO, and C6H4C(H-2) NO + OH. The predicted rate constants in the 500-2000 K temperature range indicate that anthranil production, taking place initially by intramolecular H-abstraction from the CH3 group by NO2 followed by five-membered ring formation and dehydration, dominates at temperatures below 1000 K, whereas NO2 elimination becomes predominant above 1100 K and CH3C6H4O formation by the nitro-nitrite isomerization/decomposition process accounts for only 5-11% of the total product yield in the middle temperature range 800-1300 K. The branching ratio for CH2C6H4NO formation by the decomposition process of CH2C6H4N(O)OH is negligible. The predicted high-pressure-limit rate constants with the rate expression of 4.10 x 10(17) exp[-37000/T] s(-1) for the NO2 elimination channel and 9.09 x 10(12) exp[-25800/T] s(-1) for the H2O elimination channel generally agree reasonably with available experimental data. The predicted high-pressure-limit rate constants for the NO and OH elimination channels are represented as 1.49 x 10(14) exp[-30000/T] and 1.31 x 10(15) exp[-38000/T] s(-1), respectively.
Ab initio chemical kinetics for the reactions of N(2) with singlet and triplet C(2)O radicals
(2010-03-22)
Zhu, R. S.
;
Xu, S. C.
;
Lin, M. C.
;
交大名義發表
;
National Chiao Tung University
The possible energy pathways for the reactions of N(2) with singlet and tripled C(2)O have been investigated at the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) level of theory. Our results show that the rate-controlling transition states for the formation of (3)CNN + CO, NCO + CN and (3)NCN + CO through triplet surface have 36.2, 57.7 and 60.5 kcal/mol barriers relative to the reactants (3)C(2)O + N(2). Formation of (1)CNN + CO and (1)NCN + CO via the singlet surface needs to overcome 43.7 and 66.9 kcal/mol barriers. The dominant products are (1,3)CNN + CO and cyc-(1)NCN + CO, their rate constants in cm(3) molecule (1) s (1) can be presented as k(1) ((3)CNN + CO) = 3.5 x 10(-11) exp(-36.8 kcal/mol/RT), k(2) ((1)CNN + CO) <= 2.9 x 10(-12) exp(-33.2 kcal/mol/RT) and k(3) (cyc-(1)NCN + CO) = 6.86 x 10(-20)exp(-27.7 kcal/mol/RT), which are signi. cantly lower than those assumed in the literature. The rate constants for the formation of (3)NCN + CO and NCO + CN are too small to be important due to their high exit barriers. The predicted heats of reaction for formation of products NCO + CN, (3)CNN + CO and (3)NCN + CO are 45.9, 18.1 and -10.7 kcal/mol, which agree excellently with the experimental values, 45.8, 17.7 and -10.7 kcal/mol. Our results imply that the reaction of C(2)O with N2 cannot compete with the CH + N(2) reaction for prompt-NO formation in hydrocarbon combustion. (C) 2010 Elsevier B. V. All rights reserved.
Ab initio chemical kinetics for the reactions of N-2 with singlet and triplet C2O radicals
(2010-03-22)
Zhu, R. S.
;
Xu, S. C.
;
Lin, M. C.
;
交大名義發表
;
National Chiao Tung University
The possible energy pathways for the reactions of N-2 with singlet and tripled C2O have been investigated at the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) level of theory. Our results show that the rate-controlling transition states for the formation of (CNN)-C-3 + CO, NCO + CN and (NCN)-N-3 + CO through triplet surface have 36.2, 57.7 and 60.5 kcal/mol barriers relative to the reactants (C2O)-C-3 + N-2. Formation of (CNN)-C-1 + CO and (NCN)-N-1 + CO via the singlet surface needs to overcome 43.7 and 66.9 kcal/mol barriers. The dominant products are (CNN)-C-1,3 + CO and cyc-(NCN)-N-1 + CO, their rate constants in cm(3) molecule (1) s (1) can be presented as k(1) ((CNN)-C-3 + CO) = 3.5 x 10(-11) exp(-36.8 kcal/mol/RT), k(2) ((CNN)-C-1 + CO) <= 2.9 x 10(-12) exp(-33.2 kcal/mol/RT) and k(3) (cyc-(NCN)-N-1 + CO) = 6.86 x 10(-20)exp(-27.7 kcal/mol/RT), which are signi. cantly lower than those assumed in the literature. The rate constants for the formation of (NCN)-N-3 + CO and NCO + CN are too small to be important due to their high exit barriers. The predicted heats of reaction for formation of products NCO + CN, (CNN)-C-3 + CO and (NCN)-N-3 + CO are 45.9, 18.1 and -10.7 kcal/mol, which agree excellently with the experimental values, 45.8, 17.7 and -10.7 kcal/mol. Our results imply that the reaction of C2O with N2 cannot compete with the CH + N-2 reaction for prompt-NO formation in hydrocarbon combustion. (C) 2010 Elsevier B. V. All rights reserved.
Quantum Chemical Prediction of Pathways; and Rate Constants for Reactions of CO and CO(2) with Vacancy Defects on Graphite (0001) Surfaces
(2009-10-29)
Xu, S. C.
;
Irle, S.
;
Musaev, D. G.
;
Lin, M. C.
;
應用化學系分子科學碩博班
We present reaction pathways for adsorption of CO and CO(2) molecules in the vicinity of monovacancy defects on graphite (0001) based on B3LYP and dispersion-augmented density-functional tight-binding (DFTB-D) studies of the potential energy surfaces (PES) of these reactions. To model the graphite (0001) monovacancy defects, finite-size molecular model systems up to the size of dicircumcoronene (C(95)H(24)) were employed. We find that the CO molecule reacts readily with the monovacancy defects and partially "heals" the carbon hexagon network leading to the formation of a stable epoxide, whereas CO(2) oxidizes the defect via a dissociative adsorption pathway following CO elimination. We predict reaction rate constants in the temperature range between 300 and 3000 K using Rice-Ramsperger-Kassel-Marcus theory. Quantum chemical molecular dynamics simulations at 3000 K based on on-the-fly DFTB-D energies and gradients-support the results of our PES studies.
Quantum Chemical Prediction of Pathways; and Rate Constants for Reactions of CO and CO2 with Vacancy Defects on Graphite (0001) Surfaces
(2009-10-29)
Xu, S. C.
;
Irle, S.
;
Musaev, D. G.
;
Lin, M. C.
;
應用化學系分子科學碩博班
We present reaction pathways for adsorption of CO and CO2 molecules in the vicinity of monovacancy defects on graphite (0001) based on B3LYP and dispersion-augmented density-functional tight-binding (DFTB-D) studies of the potential energy surfaces (PES) of these reactions. To model the graphite (0001) monovacancy defects, finite-size molecular model systems up to the size of dicircumcoronene (C95H24) were employed. We find that the CO molecule reacts readily with the monovacancy defects and partially "heals" the carbon hexagon network leading to the formation of a stable epoxide, whereas CO2 oxidizes the defect via a dissociative adsorption pathway following CO elimination. We predict reaction rate constants in the temperature range between 300 and 3000 K using Rice-Ramsperger-Kassel-Marcus theory. Quantum chemical molecular dynamics simulations at 3000 K based on on-the-fly DFTB-D energies and gradients-support the results of our PES studies.
Quantum Chemical Prediction of Reaction Pathways and Rate Constants for Reactions of NO and NO(2) with Monovacancy Defects on Graphite (0001) Surfaces
(2010-05-13)
Xu, S. C.
;
Irle, S.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We present reaction pathways for adsorption reactions of NO and NO(2) molecules in the vicinity of monovacancy defects on graphite (0001) based on quantum chemical potential energy surfaces (PESs) obtained by B3LYP and dispersion-augmented density-functional tight-binding (DFTB-D) methods. To model the graphite (0001) monovacancy defects, finite-size molecular model systems up to the size of dicircumcoronene (C(95)H(24)) were employed. We find that the reactions of NO(x) on the monodefective graphite surface are initiated by rapid association processes with negligible barriers, leading to nitridation and oxidation of the graphite surface, and eventually producing gaseous CO(x), NO, and CN species leaving from an even more defective graphite surface. On the basis of the computed reaction pathways, we predict reaction rate constants in the temperature range between 300 and 3000 K using Rice-Ramsperger-Kassel-Marcus theory. High-temperature quantum chemical molecular dynamics simulations at 3000 K based on on-the-fly DFTB-D energies and gradients support the results of our PES studies.
Quantum Chemical Prediction of Reaction Pathways and Rate Constants for Reactions of NO and NO2 with Monovacancy Defects on Graphite (0001) Surfaces
(2010-05-13)
Xu, S. C.
;
Irle, S.
;
Lin, M. C.
;
應用化學系
;
Department of Applied Chemistry
We present reaction pathways for adsorption reactions of NO and NO2 molecules in the vicinity of monovacancy defects on graphite (0001) based on quantum chemical potential energy surfaces (PESs) obtained by B3LYP and dispersion-augmented density-functional tight-binding (DFTB-D) methods. To model the graphite (0001) monovacancy defects, finite-size molecular model systems up to the size of dicircumcoronene (C95H24) were employed. We find that the reactions of NOx on the monodefective graphite surface are initiated by rapid association processes with negligible barriers, leading to nitridation and oxidation of the graphite surface, and eventually producing gaseous COx, NO, and CN species leaving from an even more defective graphite surface. On the basis of the computed reaction pathways, we predict reaction rate constants in the temperature range between 300 and 3000 K using Rice-Ramsperger-Kassel-Marcus theory. High-temperature quantum chemical molecular dynamics simulations at 3000 K based on on-the-fly DFTB-D energies and gradients support the results of our PES studies.
Quantum Chemical Prediction of Reaction Pathways and Rate Constants for the Reactions of O-x (x=1 and 2) with Pristine and Defective Graphite (0001) Surfaces
(2012-01-19)
Xu, S. C.
;
Chen, Hui-Lung
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We present reaction pathways for adsorption reactions of the O atom and O-2 molecule in the pristine and monovacancy defective graphite (0001) based on quantum chemical potential energy surfaces (PESs) obtained by the dispersion-augmented density-functional tight-binding (DFTB-D) method. We use a dicircumcoronene C96H24 (L0D) graphene slab as the pristine graphite (0001) model and dicircumcoronene C95H24 (LIV) as the graphite (0001) monovacancy defect model. We found that the adsorption reactions of O and O-2 on the L0D surface can produce defects on the graphite surface. O can yield CO, while O-2 can yield both CO and CO2 molecules. The adsorption reactions of the O and O-2 on the LW surface can produce a 2-C defective graphite surface and CO, and CO and CO2, respectively. The O and O-2 more readily oxidize the defected surface, LIV, than the defect-free surface, L0D. On the basis of the computed reaction pathways, we predict reaction rate constants in the temperature range between 300 and 3000 K using Rice-Ramsperger-Kassel-Marcus (RRKM) theory. High-temperature quantum chemical molecular dynamics simulations at 3000 K based on on-the-fly DFTB-D energies and gradients support the results of our PES studies.