Browsing by Author "Xu, Shucheng"

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Ab Initio Chemical Kinetics for Singlet CH(2) Reaction with N(2) and the Related Decomposition of Diazomethane
(2010-04-22)
Xu, Shucheng
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism for the reaction of singlet state CH(2) with N(2) have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of the reactions has been calculated by single-point calculations at the CCSD(T)/6-311+G(3df,2p) level based on geometries optimized at the B3LYP/6-311+G(3df,2p) level. By comparing the differences in the predicted heats of reaction with the available experimental values, we estimate the uncertainties in the calculated heats of reactions are +/- 1.4 kcal/mol. Rate constants for various product channels in the temperature range of 300-3000 K are predicted by the variational transition state and RRKM theories. The predicted total rate constants for (1)CH(2) + N(2) at 760 Torr Ar pressure can be represented by the expressions s-k(total) = 9.67 x 10(+7) x T(-6.88) exp (-1345/T) cm(3) molecule(-1) s(-1) at T = 300-2400 K and 3.15 x 10(-229) x T(+56.18) exp (128 000/T) cm(3) molecule(-1) s(-1) at T = 2400-3000 K. The branching ratios of the primary channels for (1)CH(2) + N(2) are predicted: k(1) for forming singlet s-CH(2)N(2)-a (diazomethane) accounts for 0.97-0.01, k(2) + k(4) for producing HCNN-a + H accounts for 0.00-0.69, k(3) for forming singlet s-CH(2)N(2)-b (3H-diazirine) accounts for 0.03-0.00, k(5) for producing HCN + NH accounts for 0.00-0.18, and k(6) for producing CNNH + H accounts for 0.00-0.11 in the temperature range of 300-3000 K. The rate constant predicted for the unimoclecular decomposition of diazomethane producing (1)CH(2) + N(2) agrees closely with experimental results. Because of the low stability of the two isomeric CH(2)N(2) adducts and the high barriers for production of CN-containing products, the contribution of the CH(2) + N(2) reaction to NO formation becomes very small.
Ab Initio Chemical Kinetics for Singlet CH2 Reaction with N-2 and the Related Decomposition of Diazomethane
(2010-04-22)
Xu, Shucheng
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism for the reaction of singlet state CH2 with N-2 have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of the reactions has been calculated by single-point calculations at the CCSD(T)/6-311+G(3df,2p) level based on geometries optimized at the B3LYP/6-311+G(3df,2p) level. By comparing the differences in the predicted heats of reaction with the available experimental values, we estimate the uncertainties in the calculated heats of reactions are +/- 1.4 kcal/mol. Rate constants for various product channels in the temperature range of 300-3000 K are predicted by the variational transition state and RRKM theories. The predicted total rate constants for (CH2)-C-1 + N-2 at 760 Torr Ar pressure can be represented by the expressions s-k(total) = 9.67 x 10(+7) x T-6.88 exp (-1345/T) cm(3) molecule(-1) s(-1) at T = 300-2400 K and 3.15 x 10(-229) x T+56.18 exp (128 000/T) cm(3) molecule(-1) s(-1) at T = 2400-3000 K. The branching ratios of the primary channels for (CH2)-C-1 + N-2 are predicted: k(1) for forming singlet s-CH2N2-a (diazomethane) accounts for 0.97-0.01, k(2) + k(4) for producing HCNN-a + H accounts for 0.00-0.69, k(3) for forming singlet s-CH2N2-b (3H-diazirine) accounts for 0.03-0.00, k(5) for producing HCN + NH accounts for 0.00-0.18, and k(6) for producing CNNH + H accounts for 0.00-0.11 in the temperature range of 300-3000 K. The rate constant predicted for the unimoclecular decomposition of diazomethane producing (CH2)-C-1 + N-2 agrees closely with experimental results. Because of the low stability of the two isomeric CH2N2 adducts and the high barriers for production of CN-containing products, the contribution of the CH2 + N-2 reaction to NO formation becomes very small.
Ab Initio Chemical Kinetics for the HCCO plus H Reaction
(2016)
Pham-Cam Nam
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Raghunath, P.
;
Huynh, Lam K.
;
Xu, Shucheng
;
Lin, M. C.
Ketenyl radical (HCCO) is an important hydrocarbon combustion intermediate. The mechanisms and kinetics for the reaction of HCCO (X(2)A \'\') with H(S-2) occurring on both singlet and triplet surfaces have been studied by a combination of ab initio calculations and rate constant predictions at the CCSD(T)/6-311++ G(3df,2p)//CCSD/6-311++G(d,p) level of theory. The kinetics and product branching ratios have been investigated in the temperature range of 297-3000 K by variational transition state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories for the production of CH2(a(1)A(1)) + CO(X-1 Sigma(+)) and CH2((XB1)-B-3) + CO(X-1 Sigma(+)). Our prediction for the primary product CH2(a(1)A(1)) + CO(X-1 Sigma(+)) formation is in good agreement with earlier experimental results. The pressure independent rate constant for this channel can be expressed by k(1) (T) = 8.62 x 10(-11)T(0.16)exp(-20/T) cm(3) molecule(-1) s(-1). For the production of CH2((XB1)-B-3) + CO(X-1 Sigma(+)), the rate constant k(2) can be represented as k(2)(T) = 7.63 x 10(-16)T(1.56)exp(-386/T) cm(3) molecule(-1) s(-1). The predicted product branching ratios for the reaction are in close agreement with experimental data as well. We also predicted the heat of formation at 0 K for (HCCO)-H-2, (CCO)-C-3, and (CCO)-C-1 by CCSD(T)/6-311++ G(3df,2p), CBS-QB3, and G2M; the values are in good agreement among one another. Specifically, the CCSD(T) values are:Delta H-f degrees(HCCO, X2A \'\') = 42.52 +/- 0.70; Delta H-f degrees(CCO, (XSg)-S-3) = 91.50 +/- 0.54; and Delta H-f degrees(CCO, a(1)Delta) = 110.22 +/- 0.54 kcal/mol.
Ab Initio Chemical Kinetics for the NH(2) + HNO(x) Reactions, Part I: Kinetics and Mechanism for NH(2) + HNO
(2009-11-01)
Xu, Shucheng
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism for the reaction of NH(2) with HNO have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The major products of this reaction were found to be NH(3) + NO formed by H-abstraction via a long-lived H(2)N center dot center dot center dot HNO complex and the H(2)NN(H)O radical intermediate formed by association with 26.9 kcal/mol binding energy. The rate constants for formation of primary products in the temperature range of 300-3000 K were predicted by variational transition state or RRKM theories. The predicted total rate constants at the 760 Torr At pressure can be represented by k(total) = 3.83 x 10(-20) x T(+2.47)exp(1450/T) at T = 300-600 K; 2.58 x 10(-22) x T(+3.15) exp(1831/T) cm(3) molecule(-1) s(-1) at T = 600-3000 K. The branching ratios of major channels at 760 Torr Ar pressure are predicted: k(1) + k(3) + k(4) producing NH(3) + NO accounts for 0.59-0.90 at T = 300-3000 K peaking around 1000 K, k(2) accounts for 0.41-0.03 at T = 300-600 K decreasing with temperature, and k(5) accounts for 0.07-0.27 at T > 600 K increasing gradually with temperature. The NH3 + NO formation rate constant was found to be a factor of 3-10 smaller than that of the isoelectronic reaction CH(3) + HNO producing CH(4) + NO, which has been shown to take place by barrierless H-abstraction without involving a hydrogen-bonding complex as in the NH(2) case. (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 667-677, 2009
Ab initio Chemical Kinetics for the NH(2) + HNO(x) Reactions, Part II: Kinetics and Mechanism for NH(2) + HONO
(2009-11-01)
Xu, Shucheng
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism for the reaction of NH(2) with HONO have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The reaction producing the primary products, NH(3) + NO(2), takes place via precomplexes, H(2)N center dot center dot center dot c-HONO or H(2)N center dot center dot center dot t-HONO with binding energies, 5.0 or 5.9 kcal/mol, respectively. The rate constants for the major reaction channels in the temperature range of 300-3000 K are predicted by variational transition state theory or Rice-Ramsperger-Kassel-Marcus theory depending on the mechanism involved. The total rate constant can be represented by k(total) = 1.69 x 10(-20) x T(2.34) exp(1612/T) cm(3) molecule(-1) s(-1) at T =300-650 K and 8.04 x 10(-22) x T(3.36) exp(2303/T) cm(3) molecule(-1) s(-1) at T =650-3000 K, The branching ratios of the major channels are predicted: k(1) + k(3) producing NH(3) + NO(2) accounts for 1.00-0.98 in the temperature range 300-3000 K and k(2) producing OH + H(2)NNO accounts for 0.02 at T > 2500 K. The predicted rate constant for the reverse reaction, NH(3) + NO(2) -> NH(2) + HONO represented by 8.00 x 10(-26) x T(4.25) exp(-11,560/T) cm(3) molecule(-1) s(-1), is in good agreement with the experimental data. (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 678-688, 2009
Ab Initio Chemical Kinetics for the NH(2) + HNO(x) Reactions, Part III: Kinetics and Mechanism for NH(2) + HONO(2)
(2010-02-01)
Xu, Shucheng
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism for the reaction of NH(2) with HONO(2) have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single-point calculations at the CCSD(T)/6311 +G(3df, 2p) level based on geometries optimized at the B3LYP/6-311 +G(3df, 2p) level. The reaction producing the primary products, NH(3) + NO(3), takes place via a precursor complex, H(2)N center dot center dot center dot HONO(2) with an 8.4-kcal/mol binding energy. The rate constants for major product channels in the temperature range 200-3000 K are predicted by variational transition state or variational Rice-Ramsperger-Kassel-Marcus theory. The results show that the reaction has a noticeable pressure dependence at T < 900 K. The total rate constants at 760 Torr Ar-pressure can be represented by k(total) = 1.71 x 10(-3) x T(-3.85) exp(-96/T) cm(3) molecule(-1) s(-1) at T = 200-550 K, 5.11 X 10(-23) x T(+3.22) exp(70/T) cm(3) molecule(-1) s(-1) at T = 550-3000 K. The branching ratios of primary channels at 760 Torr Ar-pressure are predicted: k(1) producing NH(3) + NO(3) accounts for 1,00-0,99 in the temperature range of 200-3000 K and k(2) + k(3) producing H(2)NO + HONO accounts for less than 0.01 when temperature is more than 2600 K. The reverse reaction, NH(3) + NO(3) -> NH(2) + HONO(2) shows relatively weak pressure dependence at P < 100 Torr and T < 600 K due to its precursor complex, NH(3)center dot center dot center dot O(3)N with a lower binding energy of 1.8 kcal/mol, The predicted rate constants can be represented by k(-1) = 6.70 x 10(-24) x T(+3.58) exp(-850/T) cm(3) molecule(-1) s(-1) at T = 200-3000 K and 760 Torr N(2) pressure, where the predicted rate at T = 298 K, 2.8 x 10(-16) cm(3) molecule(-1) s(-1) is in good agreement with the experimental data. The NH(3) + NO(3) formation rate constant was found to be a factor of 4 smaller than that of the reaction OH + HONO(2) producing the H(2)O + NO(3) because of the lower barrier for the transition state for the OH + HONO(2) (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 69-78, 2010
Ab Initio Chemical Kinetics for the NH2 + HNOx Reactions, Part I: Kinetics and Mechanism for NH2 + HNO
(2009-11-01)
Xu, Shucheng
;
Lin, M. C.
;
應用化學系
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Department of Applied Chemistry
The kinetics and mechanism for the reaction of NH2 with HNO have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The major products of this reaction were found to be NH3 + NO formed by H-abstraction via a long-lived H2N center dot center dot center dot HNO complex and the H2NN(H)O radical intermediate formed by association with 26.9 kcal/mol binding energy. The rate constants for formation of primary products in the temperature range of 300-3000 K were predicted by variational transition state or RRKM theories. The predicted total rate constants at the 760 Torr At pressure can be represented by k(total) = 3.83 x 10(-20) x T(+2.47)exp(1450/T) at T = 300-600 K; 2.58 x 10(-22) x T+3.15 exp(1831/T) cm(3) molecule(-1) s(-1) at T = 600-3000 K. The branching ratios of major channels at 760 Torr Ar pressure are predicted: k(1) + k(3) + k(4) producing NH3 + NO accounts for 0.59-0.90 at T = 300-3000 K peaking around 1000 K, k(2) accounts for 0.41-0.03 at T = 300-600 K decreasing with temperature, and k(5) accounts for 0.07-0.27 at T > 600 K increasing gradually with temperature. The NH3 + NO formation rate constant was found to be a factor of 3-10 smaller than that of the isoelectronic reaction CH3 + HNO producing CH4 + NO, which has been shown to take place by barrierless H-abstraction without involving a hydrogen-bonding complex as in the NH2 case. (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 667-677, 2009
Ab initio Chemical Kinetics for the NH2 + HNOx Reactions, Part II: Kinetics and Mechanism for NH2 + HONO
(2009-11-01)
Xu, Shucheng
;
Lin, M. C.
;
應用化學系
;
Department of Applied Chemistry
The kinetics and mechanism for the reaction of NH2 with HONO have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The reaction producing the primary products, NH3 + NO2, takes place via precomplexes, H2N center dot center dot center dot c-HONO or H2N center dot center dot center dot t-HONO with binding energies, 5.0 or 5.9 kcal/mol, respectively. The rate constants for the major reaction channels in the temperature range of 300-3000 K are predicted by variational transition state theory or Rice-Ramsperger-Kassel-Marcus theory depending on the mechanism involved. The total rate constant can be represented by k(total) = 1.69 x 10(-20) x T-2.34 exp(1612/T) cm(3) molecule(-1) s(-1) at T =300-650 K and 8.04 x 10(-22) x T-3.36 exp(2303/T) cm(3) molecule(-1) s(-1) at T =650-3000 K, The branching ratios of the major channels are predicted: k(1) + k(3) producing NH3 + NO2 accounts for 1.00-0.98 in the temperature range 300-3000 K and k(2) producing OH + H2NNO accounts for 0.02 at T > 2500 K. The predicted rate constant for the reverse reaction, NH3 + NO2 -> NH2 + HONO represented by 8.00 x 10(-26) x T-4.25 exp(-11,560/T) cm(3) molecule(-1) s(-1), is in good agreement with the experimental data. (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 678-688, 2009
Ab Initio Chemical Kinetics for the NH2 + HNOx Reactions, Part III: Kinetics and Mechanism for NH2 + HONO2
(2010-02-01)
Xu, Shucheng
;
Lin, M. C.
;
應用化學系
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Department of Applied Chemistry
The kinetics and mechanism for the reaction of NH2 with HONO2 have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single-point calculations at the CCSD(T)/6311 +G(3df, 2p) level based on geometries optimized at the B3LYP/6-311 +G(3df, 2p) level. The reaction producing the primary products, NH3 + NO3, takes place via a precursor complex, H2N center dot center dot center dot HONO2 with an 8.4-kcal/mol binding energy. The rate constants for major product channels in the temperature range 200-3000 K are predicted by variational transition state or variational Rice-Ramsperger-Kassel-Marcus theory. The results show that the reaction has a noticeable pressure dependence at T < 900 K. The total rate constants at 760 Torr Ar-pressure can be represented by k(total) = 1.71 x 10(-3) x T-3.85 exp(-96/T) cm(3) molecule(-1) s(-1) at T = 200-550 K, 5.11 X 10(-23) x T+3.22 exp(70/T) cm(3) molecule(-1) s(-1) at T = 550-3000 K. The branching ratios of primary channels at 760 Torr Ar-pressure are predicted: k(1) producing NH3 + NO3 accounts for 1,00-0,99 in the temperature range of 200-3000 K and k(2) + k(3) producing H2NO + HONO accounts for less than 0.01 when temperature is more than 2600 K. The reverse reaction, NH3 + NO3 -> NH2 + HONO2 shows relatively weak pressure dependence at P < 100 Torr and T < 600 K due to its precursor complex, NH3 center dot center dot center dot O3N with a lower binding energy of 1.8 kcal/mol, The predicted rate constants can be represented by k(-1) = 6.70 x 10(-24) x T+3.58 exp(-850/T) cm(3) molecule(-1) s(-1) at T = 200-3000 K and 760 Torr N-2 pressure, where the predicted rate at T = 298 K, 2.8 x 10(-16) cm(3) molecule(-1) s(-1) is in good agreement with the experimental data. The NH3 + NO3 formation rate constant was found to be a factor of 4 smaller than that of the reaction OH + HONO2 producing the H2O + NO3 because of the lower barrier for the transition state for the OH + HONO2 (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 69-78, 2010
Ab initio chemical kinetics for the OH plus HNCN reaction
(2007-07-26)
Xu, Shucheng
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanism of the reaction of the cyanomidyl radical (HNCN) with the hydroxyl radical (OH) have been investigated by ab initio calculations with rate constants prediction. The single and triplet potential energy surfaces of this reaction have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df,2p) level based on geometries optimized at the B3LYP/6-311+G(3df,2p) and CCSD/6-311++ G(d,p) levels. The rate constants for various product channels in the temperature range of 300-3000 K are predicted by variational transition-state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories. The predicted total rate constants can be represented by the expressions k(total) = 2.66 x 10(+2) x T-4.50 exp(-239/T) in which T = 300-1000 K and 1.38 x 10(-20) x T-2.78 exp(1578/T) cm(3) molecule(-1) s(-1) where T = 1000-3000 K. The branching ratios of primary channels are predicted: k(1) for forming singlet HON(H)CN accounts for 0.32-0.28, and k(4) for forming singlet HONCNH accounts for 0.68-0.17 in the temperature range of 300-800 K. k(2) + k(7) for producing H2O + NCN accounts for 0.55-0.99 in the high-temperature range of 800-3000 K. The branching ratios of k(3) for producing HCN + HNO, k(6) for producing H2N + NCO, k(8) for forming (HN)-H-3(OH)CN, k(9) for producing CNOH + (NH)-N-3, and k(5) + k(10) for producing NH2 + NCO are negligible. The rate constants for key individual product channels are provided in a table for different temperature and pressure conditions.
Ab initio chemical kinetics for the reactions of HNCN with O((3)P) and O(2)
(2009-01-01)
Xu, Shucheng
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Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanisms of the reactions of cyanomidyl radical (HNCN) with oxygen atoms and molecules have been investigated by ab initio calculations with rate constant prediction. The doublet and quartet state potential energy surfaces (PESs) of the two reactions have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The rate constants for various product channels of the two reactions in the temperature range of 300-3000 K are predicted by variational transition state and RRKM theories. The predicted total rate constants of the O((3)P) + HNCN reaction at 760 Torr Ar pressure can be represented by the expressions k(total) (O + HNCN) = 3.12 x 10(-10) x T(-0.05) exp (-37/T) cm(3) molecule(-1) s(-1) at T= 300-3000 K. The branching ratios of primary channels of the O((3)P) + HNCN are predicted: k(1) for producing the NO + CNH accounts for 0.72-0.64, k(2) + k(9) for producing the (3)NH + NCO accounts for 0.27-0.32, and k(6) for producing the CN + HNO accounts for 0.01-0.07 in the temperature range studied. Meanwhile, the predicted total rate constants of the O(2) + HNCN reaction at 760 Torr Ar pressure can be represented by the expression, k(total)(O(2) + HNCN) = 2.10 x 10(-16) x T(1.28)exp (-12200/T) cm(3) molecule(-1) s(-1) at T = 300-3000 K. The predicted branching ratio for k(11) + k(13) producing HO(2) + (3)NCN as the primary products accounts for 0.98-1.00 in the temperature range studied. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Ab initio chemical kinetics for the reactions of HNCN with O(P-3) and O-2
(2009)
Xu, Shucheng
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
The kinetics and mechanisms of the reactions of cyanomidyl radical (HNCN) with oxygen atoms and molecules have been investigated by ab initio calculations with rate constant prediction. The doublet and quartet state potential energy surfaces (PESs) of the two reactions have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The rate constants for various product channels of the two reactions in the temperature range of 300-3000 K are predicted by variational transition state and RRKM theories. The predicted total rate constants of the O(P-3) + HNCN reaction at 760 Torr Ar pressure can be represented by the expressions k(total) (O + HNCN) = 3.12 x 10(-10) x T-0.05 exp (-37/T) cm(3) molecule(-1) s(-1) at T= 300-3000 K. The branching ratios of primary channels of the O(P-3) + HNCN are predicted: k(1) for producing the NO + CNH accounts for 0.72-0.64, k(2) + k(9) for producing the (NH)-N-3 + NCO accounts for 0.27-0.32, and k(6) for producing the CN + HNO accounts for 0.01-0.07 in the temperature range studied. Meanwhile, the predicted total rate constants of the O-2 + HNCN reaction at 760 Torr Ar pressure can be represented by the expression, k(total)(O-2 + HNCN) = 2.10 x 10(-16) x T(1.28)exp (-12200/T) cm(3) molecule(-1) s(-1) at T = 300-3000 K. The predicted branching ratio for k(11) + k(13) producing HO2 + (NCN)-N-3 as the primary products accounts for 0.98-1.00 in the temperature range studied. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Computational study on the kinetics and mechanisms for the unimolecular decomposition of formic and oxalic Acids
(2007-07-26)
Chang, Jee-Gong
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Chen, Hsin-Tsung
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Xu, Shucheng
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Lin, M. C.
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應用化學系分子科學碩博班
The kinetics and mechanisms for the unimolecular decomposition reactions of formic acid and oxalic acid have been studied computationally by the high-level G2M(CC1) method and microcanonical RRKM theory. There are two reaction pathways in the decomposition of formic acid: The dehydration process starting from the Z conformer is found to be the dominant, whereas the decarboxylation reaction starting from the E conformer is less competitive. The predicted rate constants for the dehydration and decarboxylation reactions are in good agreement with the experimental data. The calculated CO/CO2 ratio, 13.6-13.9 between 1300 and 2000 K, is in close agreement with the ratio of 10 measured experimentally by Hsu et al. (In The 19th International Symposium on Combustion; The Combustion Institute: Pittsburgh, PA, 1983; p 89). For oxalic acid, its isomer with two intramolecular hydrogen bonds is the most stable structure, similar to earlier reports. Two primary decomposition channels of oxalic acid producing CO2 + HOCOH with barriers of 33-36 kcal/mol and CO2 + CO + H2O with a barrier of 39 kcal/mol were found. At high temperatures, the latter process becomes more competitive. The rate constant predicted for the formation of CO2 and HOCOH (the precursor of HCOOH) agrees well with available experimental data. The mechanism for the isomerization of HOCOH to HCOOH is also discussed.
Experimental and theoretical studies of rate coefficients for the reaction O(P-3) plus C2H5OH at high temperatures
(2007-07-26)
Wu, Chih-Wei
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Lee, Yuan-Pern
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Xu, Shucheng
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Lin, M. C.
;
應用化學系
Rate coefficients of the reaction O(P-3) + C2H5OH in the temperature range 782-1410 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO2 at 193 nm with an ArF excimer laser; their concentrations were monitored via atomic resonance absorption. Our data in the range 886-1410 K are new. Combined with previous measurements at low temperature, rate coefficients determined for the temperature range 297-1410 K are represented by the following equation: k(T) = (2.89 +/- 0.09) x 10(-16)T(1.62) exp[-(1210 +/- 90)/T] cm(3) molecule(-1) s(-1); listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311+G(3df, 2p)//B3LYP/6-311+G(3df) level predict potential energies of various reaction paths. Rate coefficients are predicted with the canonical variational transition state (CVT) theory with the small curvature tunneling correction (SCT) method. Reaction paths associated with trans and gauche conformations are both identified. Predicted total rate coefficients, 1.60 x 10(-22)T(3.50) exp(16/T) cm(3) molecule(-1) s(-1) for the range 300-3000 K, agree satisfactorily with experimental observations. The branching ratios of three accessible reaction channels forming CH3CHOH + OH (1a), CH2CH2OH + OH (1b), and CH3CH2O + OH (1c) are predicted to vary distinctively with temperature. Below 500 K, reaction 1a is the predominant path; the branching ratios of reactions 1b,c become similar to 40% and similar to 11%, respectively, at 2000 K.
Photodissociation dynamics of nitrobenzene and o-nitrotoluene
(2007-02-14)
Lin, Ming-Fu
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Lee, Yuan T.
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Ni, Chi-Kung
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Xu, Shucheng
;
Lin, M. C.
Photodissociation of nitrobenzene at 193, 248, and 266 nm and o-nitrotoluene at 193 and 248 nm was investigated separately using multimass ion imaging techniques. Fragments corresponding to NO and NO2 elimination from both nitrobenzene and o-nitrotoluene were observed. The translational energy distributions for the NO elimination channel show bimodal distributions, indicating two dissociation mechanisms involved in the dissociation process. The branching ratios between NO and NO2 elimination channels were determined to be NO/NO2=0.32 +/- 0.12 (193 nm), 0.26 +/- 0.12 (248 nm), and 0.4 +/- 0.12(266 nm) for nitrobenzene and 0.42 +/- 0.12(193 nm) and 0.3 +/- 0.12 (248 nm) for o-nitrotoluene. Additional dissociation channels, O atom elimination from nitrobenzene, and OH elimination from o-nitrotoluene, were observed. New dissociation mechanisms were proposed, and the results are compared with potential energy surfaces obtained from ab initio calculations. Observed absorption bands of photodissociation are assigned by the assistance of the ab initio calculations for the relative energies of the triplet excited states and the vertical excitation energies of the singlet and triplet excited states of nitrobenzene and o-nitrotoluene. Finally, the dissociation rates and lifetimes of photodissociation of nitrobenzene and o-nitrotoluene were predicted and compared to experimental results. (c) 2007 American Institute of Physics.
Photodissociation dynamics of nitrobenzene and o-nitrotoluene
(2007-02-14)
Lin, Ming-Fu
;
Lee, Yuan T.
;
Ni, Chi-Kung
;
Xu, Shucheng
;
Lin, M. C.
Photodissociation of nitrobenzene at 193, 248, and 266 nm and o-nitrotoluene at 193 and 248 nm was investigated separately using multimass ion imaging techniques. Fragments corresponding to NO and NO2 elimination from both nitrobenzene and o-nitrotoluene were observed. The translational energy distributions for the NO elimination channel show bimodal distributions, indicating two dissociation mechanisms involved in the dissociation process. The branching ratios between NO and NO2 elimination channels were determined to be NO/NO2=0.32 +/- 0.12 (193 nm), 0.26 +/- 0.12 (248 nm), and 0.4 +/- 0.12(266 nm) for nitrobenzene and 0.42 +/- 0.12(193 nm) and 0.3 +/- 0.12 (248 nm) for o-nitrotoluene. Additional dissociation channels, O atom elimination from nitrobenzene, and OH elimination from o-nitrotoluene, were observed. New dissociation mechanisms were proposed, and the results are compared with potential energy surfaces obtained from ab initio calculations. Observed absorption bands of photodissociation are assigned by the assistance of the ab initio calculations for the relative energies of the triplet excited states and the vertical excitation energies of the singlet and triplet excited states of nitrobenzene and o-nitrotoluene. Finally, the dissociation rates and lifetimes of photodissociation of nitrobenzene and o-nitrotoluene were predicted and compared to experimental results. (c) 2007 American Institute of Physics.