Browsing by Author "Zhu, R. S."

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A computational study on the decomposition of NH4ClO4: Comparison of the gas-phase and condensed-phase results
(2006-11-24)
Zhu, R. S.
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Lin, M. C.
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交大名義發表
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National Chiao Tung University
The decomposition of NH4ClO4 (AP) in both gaseous and condensed phases has been studied at the CCSD(T)/6-311 + G(3df,2p)// B3LYP/6-311 + G(3df,2p) level. Formation of NH3 + HClO3 is the main channel in the gas phase with 14.2 kcal/mol enthalpy change. In solution, the enthalpy change for this channel is 29.5 kcal/mol, which is close to the sublimation activation energy, similar to 30 kcal/mol in crystalline AP. Formation of H3N-HO +ClO3 has higher enthalpy changes, 56.3 kcal/mol and 77.1 kcal/mol in the gas phase and in solution, respectively. Strong solvent effects may exist in the AP decomposition reaction. (c) 2006 Elsevier B.V. All rights reserved.
Ab Initio Chemical Kinetics for the Hydrolysis of N2O4 Isomers in the Gas Phase
(2012-05-10)
Zhu, R. S.
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Lai, Ke-Yu
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Lin, M. C.
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應用化學系分子科學碩博班
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Institute of Molecular science
The mechanism and kinetics for the gas-phase hydrolysis of N2O4 isomers have been investigated at the CCSD (T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p) level of theory in conjunction with statistical rate constant calculations. Calculated results show that the contribution from the commonly assumed redox reaction of sym-N2O4 to the homogeneous gas-phase hydrolysis of NO2 can be unequivocally ruled out due to the high barrier (37.6 kcal/mol) involved; instead, t-ONONO2 directly formed by the association of 2NO(2), was found to play the key role in the hydrolysis process. The kinetics for the hydrolysis reaction, 2NO(2) + H2O <-> HONO + HNO3 (A) can be quatitatively interpreted by the two step mechanism: 2NO(2) -> t-ONONO2, t-ONONO2 + H2O -> HONO + HNO3. The predicted total forward and reverse rate constants for reaction (A), k(tf) = 5.36 x 10(-50)T(3.95) exp(1825/T) cm(6) molecule(-2) s(-1) and k(tr) = 3.31 X 10(-19)T(2.478) exp(-3199/T) cm(3) molecule(-1) s(-1), respectively, in the temperature range 200-2500 K, are in good agreement with the available experimental data.
Ab initio chemical kinetics for the reactions of N(2) with singlet and triplet C(2)O radicals
(2010-03-22)
Zhu, R. S.
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Xu, S. C.
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Lin, M. C.
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交大名義發表
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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.
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Xu, S. C.
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Lin, M. C.
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交大名義發表
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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.
Ab initio study of the ClO+NH2 reaction: Prediction of the total rate constant and product branching ratios
(2007-05-17)
Zhu, R. S.
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Lin, M. C.
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交大名義發表
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National Chiao Tung University
The mechanism for ClO + NH2 has been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the B3LYP/6-311+G(3df,2p) level and their energies have been refined by single-point calculations with the modified Gaussian-2 method, G2M(CC2). Ten stable isomers have been located and a detailed potential energy diagram is provided. The rate constants and branching ratios for the low-lying energy channel products including HCl + HNO, Cl + NH2O, and HOCl + (NH)-N-3 (X-3 Sigma(-)) are calculated. The result shows that formation of HCl + HNO is dominant below 1000 K; over 1000 K, Cl + NH2O products become dominant. However, the formation of HOCl + (NH)-N-3 (X-3 Sigma(-)) is unimportant below 1500 K. The pressure-independent individual and total rate constants can be expressed as k(1)(HCl + HNO) = 4.7 x 10(-8)(T-1.08) exp((-129)/(T)), k(2)(Cl + NH2O) = 1.7 x 10(-9)(T-0.62) exp((-24)/(T)), k(3)(HOCl + NH) = 4.8 x 10(-29)(T-5.11) exp((-1035)/(T)), and k(total) = 5.0 x 10(-9)(T-0.67) exp((-1.2)/(T)), respectively, with units of cm(3) molecule(-1) s(-1), in the temperature range of 200-2500 K.
CH(3)NO(2) decomposition/isomerization mechanism and product branching ratios: An ab initio chemical kinetic study
(2009-08-17)
Zhu, R. S.
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Lin, M. C.
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交大名義發表
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National Chiao Tung University
The low-lying energy pathways for the decomposition/isomerization of nitromethane (NM) have been investigated using different molecular orbital methods. Our results show that in addition to the commonly known CH(3) + NO(2) products formed by direct C-N bond breaking and the trans-CH(3)ONO formed by nitro-nitrite isomerization, NM can also isomerize to cis-CH(3)ONO via a very loose transition state (TS) lying 59.2 kcal/mol above CH(3)NO(2) or 0.6 kcal/mol below the CH(3) + NO(2) asymptote predicted at the UCCSD(T)/CBS level of theory. Kinetic results indicate that in the energy range of 59 +/- 1 kcal/mol, production of CH(3)O + NO is dominant, whereas above the C-N bond breaking threshold, the formation of CH(3) + NO(2) sharply increases and becomes dominant. The k(E) values predicted at different energies clearly indicate that CH(3)O + NO could be detected in an infrared multi-photon dissociation study, whereas in UV dissociation experiments with energies high above the C-N bond breaking threshold the CH(3) + NO(2) products are generated predominantly. (C) 2009 Elsevier B. V. All rights reserved.
CH3NO2 decomposition/isomerization mechanism and product branching ratios: An ab initio chemical kinetic study
(2009-08-17)
Zhu, R. S.
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Lin, M. C.
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交大名義發表
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National Chiao Tung University
The low-lying energy pathways for the decomposition/isomerization of nitromethane (NM) have been investigated using different molecular orbital methods. Our results show that in addition to the commonly known CH3 + NO2 products formed by direct C-N bond breaking and the trans-CH3ONO formed by nitro-nitrite isomerization, NM can also isomerize to cis-CH3ONO via a very loose transition state (TS) lying 59.2 kcal/mol above CH3NO2 or 0.6 kcal/mol below the CH3 + NO2 asymptote predicted at the UCCSD(T)/CBS level of theory. Kinetic results indicate that in the energy range of 59 +/- 1 kcal/mol, production of CH3O + NO is dominant, whereas above the C-N bond breaking threshold, the formation of CH3 + NO2 sharply increases and becomes dominant. The k(E) values predicted at different energies clearly indicate that CH3O + NO could be detected in an infrared multi-photon dissociation study, whereas in UV dissociation experiments with energies high above the C-N bond breaking threshold the CH3 + NO2 products are generated predominantly. (C) 2009 Elsevier B. V. All rights reserved.
Effect of Roaming Transition States upon Product Branching in the Thermal Decomposition of CH3NO2
(2013-08-15)
Zhu, R. S.
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Raghunath, P.
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Lin, M. C.
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應用化學系分子科學碩博班
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Institute of Molecular science
The kinetics for the thermal unimolecular decomposition of CH3NO2 and its structural isomer CH3ONO have been investigated by statistical theory calculations based on the potential energy surface calculated at the UCCSD(T)/CBS and CASPT3(8, 8)/6-311+G(3df,2p) levels. Our results show that for the decomposition of CH3NO2 at pressures less than 2 Torr, isomerization to CH3ONO via the recently located roaming transition state is dominant in the entire temperature range studied, 400-3000 K. However, at higher pressures, the formation of the commonly assumed products, CH3 + NO2, becomes competitive and at pressures higher than 200 Torr the production of CH3 + NO2 is exclusive. The predicted rate constants for 760 Torr and the high-pressure limit with Ar as diluent in the temperature range 500-3000 K, producing solely CH3 + NO2, can be expressed respectively by k(d)(760)(CH3NO2) = 2.94 x 10(55)T(-12.6) exp(-35500/T) s(-1) and k(d)(infinity)(CH3NO2) = 5.88 x 10(24)T(-235) exp(-31400/T) s(-1). In the low pressure limit, the decomposition reaction takes place exclusively via the roaming TS producing internally excited CH3ONO, giving rise to both CH3O + NO and CH2O + HNO with the second-order rate constant k(d)(0)(CH3NO2) = 1.17 x 10(31)T(-10.94) exp(-32400/T) cm(3) molecule(-1) s(-1). For CH3ONO decomposition, a new roaming transition state connecting to the CH2O + HNO products has been located, lying 6.8 kcal/mol below the well-known four-member ring tight transition state and 0.7 kcal/mol below CH3O + NO. The rate constants predicted by similar calculations give rise to the following expressions for the thermal decomposition of CH3ONO in He: k(d)(760)(CH3ONO) = 8.75 X 10(41)T(-8.97) exp(-22600/T) s(-1) and k(d)(infinity)(CH3ONO) = 1.58 x 10(23)T(-2.18) exp(-21100/T) s(-1) in the temperature range 300-3000 K. These results are in very good agreement with available experimental data obtained under practical pressure conditions. The much different branching ratios for the formation of CH3O + NO and CH2O + HNO in the decomposition of both CH3NO2 and CH3ONO are also given in this work.
Experimental and theoretical investigation of rate coefficients of the reaction S(P-3)+OCS in the temperature range of 298-985 K
(2006-10-28)
Lu, Chih-Wei
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Wu, Yu-Jong
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Lee, Yuan-Pern
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Zhu, R. S.
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Lin, M. C.
The reaction S(P-3)+OCS in Ar was investigated over the pressure range of 50-710 Torr and the temperature range of 298-985 K with the laser photolysis technique. S atoms were generated by photolysis of OCS with light at 248 nm from a KrF excimer laser; their concentration was monitored via resonance fluorescence excited by atomic emission of S produced from microwave-discharged SO2. At pressures less than 250 Torr, our measurements give k(298 K)=(2.7 +/- 0.5)x10(-15) cm(3) molecule(-1) s(-1), in satisfactory agreement with a previous report by Klemm and Davis [J. Phys. Chem. 78, 1137 (1974)]. New data determined for 407-985 K connect rate coefficients reported previously for T >= 860 and T <= 478 K and show a non-Arrhenius behavior. Combining our results with data reported at high temperatures, we derived an expression k(T)=(6.1 +/- 0.3)x10(-18) T-1.97 +/- 0.24 exp[-(1560 +/- 170)/T] cm(3) molecule(-1) s(-1) for 298 <= T/K <= 1680. At 298 K and P >= 500 Torr, the reaction rate was enhanced. Theoretical calculations at the G2M(CC2) level, using geometries optimized with the B3LYP/6-311+G(3df) method, yield energies of transition states and products relative to those of the reactants. Rate coefficients predicted with multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) calculations agree satisfactorily with experimental observations. According to our calculations, the singlet channel involving formation of SSCO followed by direct dissociation into S-2(a (1)Delta(g))+CO dominates below 2000 K; SSCO is formed via intersystem crossing from the triplet surface. At low temperature and under high pressure the stabilization of OCS2, formed via isomerization of SSCO, becomes important; its formation and further reaction with S atoms partially account for the observed increase in the rate coefficient under such conditions. (c) 2006 American Institute of Physics.
Mechanism and Kinetics for Ammonium Dinitramide (ADN) Sublimation: A First-Principles Study
(2012-11-08)
Zhu, R. S.
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Chen, Hui-Lung
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Lin, M. C.
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應用化學系分子科學碩博班
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Institute of Molecular science
The mechanism for sublimation of NH4N(NO2)(2) (ADN) has been investigated quantum-mechanically with generalized gradient approximation plane-wave density functional theory calculations; the solid surface is represented by a slab model and the periodic boundary conditions are applied. The calculated lattice constants for the bulk ADN, which were found to consist of NH4+[ON(O)NNO2](-) units, instead of NH4+[N(NO2)(2)](-), agree quite well with experimental values. Results show that three steps are involved in the sublimation/decomposition of ADN. The first step is the relaxation of the surface layer with 1.6 kcal/mol energy per NH4ON(O)NNO2 unit; the second step is the sublimation of the surface layer to form a molecular [NH3]-[HON(O)NNO2] complex with a 29.4 kcal/mol sublimation energy, consistent with the experimental observation of Korobeinichev et al.(10) The last step is the dissociation of the [H3N]-[HON(O)NNO2] complex to give NH3 and HON(O)NNO2 with the dissociation energy of 13.9 kcal/mol. Direct formation of NO2 (g) from solid ADN costs a much higher energy, 58.3 kcal/mol. Our calculated total sublimation enthalpy for ADN(s) -> NH3(g) + HON(O)NNO2) (g), 44.9 kcal/mol via three steps, is in good agreement with the value, 42.1 kcal/mol predicted for the one-step sublimation process in this work and the value 44.0 kcal/mol computed by Politzer et al.(11) using experimental thermochemical data. The sublimation rate constant for the rate-controlling step 2 can be represented as k(sub) = 2.18 x 10(12) exp (-30.5 kcal/mol/RT) s(-1), which agrees well with available experimental data within the temperature range studied. The high pressure limit decomposition rate constant for the molecular complex H3N center dot center dot center dot HON(O)NNO2 can be expressed by k(dec) = 3.18 x 10(13) exp (-15.09 kcal/mol/RT) s(-1). In addition, water molecules were found to increase the sublimation enthalpy of ADN, contrary to that found in the ammonium perchlorate system, in which water molecules were shown to reduce pronouncedly the enthalpy of sublimation.