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🏛️國立陽明交通大學機構典藏

Author: search.filters.author.Lin, S. H.Subject: search.filters.subject.rate constant

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Now showing 1 - 6 of 6
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    Anharmonic effect of the unimolecular dissociation of Glycerol to Glycidol
    (2018-09-01)
    Li, Qian
    ;
    Yao, Li
    ;
    Lin, S. H.
    ;
    應用化學系
    ;
    Department of Applied Chemistry
    The unimolecular dissociation rate constants of the dehydration of Glycerol to Glycidol were calculated at the MP2/6-311G(d,p) level using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The anharmonic effect of the reactions was examined by comparing the rate constants at temperatures (700-3000 K) of the canonical case and total energies (25654-53089 cm(-1)) of the microcanonical system. The calculations showed that high temperatures are required for the reaction to proceed. As the temperatures and total energies increased, the rate of reactions increased. However, the growth rate of the unimolecular dissociation rate constants was high and slower both in the canonical and microcanonical systems. Comparative analysis showed that the anharmonic effect was most significant for the reaction C -> TSC -> IV + H2O and least significant for the reaction B -> TSB1 -> I + H2O. The anharmonic effect became more significant as the temperatures and total energies increased. Compared with the microcanonical situation, the anharmonic effect of the canonical system was more pronounced.
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    Calculation of anharmonic effect on the dissociation of ethylene glycol
    (2017-12-01)
    Li, Qian
    ;
    Yao, Li
    ;
    Lin, S. H.
    ;
    應用化學系
    ;
    Department of Applied Chemistry
    The unimolecular dissociation rate constants of ethylene glycol were examined using the MP2/6-311++G(d, p) method based on the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The effect of anharmonicity on the dissociation rate constants was evaluated at 500-4000 K temperatures of the canonical system and 25,182-50,235 cm(-1) total energies of the microcanonical system. The comparison of the results showed that the H2O elimination reaction played a critical role in the decomposition processes of ethylene glycol. The results of the rate constant calculations indicated that the H2O elimination reaction dominated at low temperatures, whereas the direct C-C bond dissociation reaction (CH2OHCH2OH -> CH2OH+CH2OH) dominated at high temperatures. For channel 1, CH2OH+CH2OH, the anharmonic effect of the canonical system was not observed, while it became more obvious with the increasing total energies in the microcanonical system. For channels 2-5, CH3CHO+H2O, CH2CHOH+H2O, CH3OH+CHOH, and CH2OHCHO+H-2, the anharmonic effect of canonical and microcanonical systems became more obvious with increasing temperatures and total energies. The comparison showed that, for channels 1 and 4, C-C bond dissociation and the anharmonic effect of the microcanonical system were more evident, whereas the anharmonic effect of the canonical system was more predominant for channels 2 (CH3CHO+H2O), 3 (CH2CHOH+H2O), and 5 (CH2OHCHO+H-2).
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    Calculation of anharmonic effects in the unimolecular dissociation of M2+ (H2O)(2) (M = Be, Mg, and Ca)
    (2015-11-17)
    Li, Qian
    ;
    Yao, Li
    ;
    Xia, Wenwen
    ;
    Lin, S. H.
    ;
    應用化學系
    The anharmonic and harmonic rate constants of the unimolecular dissociation of M2+(H2O)(2) (M = Be, Mg, and Ca) were calculated using the Rice-Ramsperger-Kassel-Marcus theory. The anharmonic effects of the reactions were investigated. The results show that the energy barrier of the dissociation of Be2+(H2O)(2) is 68.47 kcal/mol, and the anharmonic (T-4000K = 4.28x10(8) s(-1)) and harmonic (T-4000K = 4.22x10(8) s(-1)) rate constants were close in value in both the canonical and microcanonical systems. The energy barriers of the two steps for the dissociation, Mg2+(H2O)(2) MgOH++H3O+, were 37.41 and 11.39 kcal/mol, and those for the dissociation, Ca2+(H2O)(2) CaOH++H3O+, were 21.15 and 26.42 kcal/mol. The anharmonic effect of the two reactions is significant and cannot be neglected in both the canonical and microcanonical systems. The comparison also shows that the rate constants of the dissociation of Ca2+(H2O)(2) have the maximum values, while those of Be2+(H2O)(2) have the minimum values in the three reactions; however, the anharmonic effect also shows the similar trend in the comparison.
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    Anharmonic effect of the unimolecular dissociation of CH3COOH
    (2014-11-02)
    Zhang, Liwei
    ;
    Yao, Li
    ;
    Li, Qian
    ;
    Wang, Guiqiu
    ;
    Lin, S. H.
    Anharmonic and harmonic rate constants of the reactions have been calculated with the Rice-Ramsperger-Kassel-Marcus theory, and the anharmonic results are higher than the harmonic ones. The anharmonic effect and isotopic effect on the decomposition reactions have also been examined. The anharmonic effect in all the four reactions is obvious, especially at the high temperatures or energies. Relatively, the anharmonic effect on the reaction trans-acetic acid -> TS2 radical is the least obvious among the four reactions. In the microcanonical system, the difference of the rate constants between the deuterated results and the non-deuterated results is not negligible; in other words, the isotopic effect is obvious in all the four reactions. Among these reactions, three of the deuterated results (d, d3 and d4) have a big difference.
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    Calculation of anharmonic effects for the unimolecular dissociation of CH3OOH and its deuterated species CD3OOD using the Rice-Ramsperger-Kassel-Marcus theory
    (2015-06-01)
    Li, Qian
    ;
    Yao, Li
    ;
    Lin, S. H.
    ;
    應用化學系
    ;
    Department of Applied Chemistry
    Anharmonic and harmonic rate constants for the unimolecular dissociation of CH3OOH and CD3OOD were calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory at the MP2/6-311++G(3df,3pd) level of theory. The anharmonic effect of the reactions was investigated. Comparison of results for the decompositions of CH3OOH and CD3OOD shows that the direct bond dissociation channel, CH3 (D-3) O + OH (D), is the most dominant reaction. The anharmonic effect plays an important role in the unimolecular dissociation of both CH3OOH and CD3OOD. For channels CH3 (D-3) O + OH (D) and CH3 (D-3) + H (D) O-2, the anharmonic effect of the unimolecular dissociation of CD3OOD is more pronounced than that of the unimolecular dissociation of CH3OOH. For channel H-2 (D-2) CO + H-2 (D-2) O, the anharmonic effect of the unimolecular dissociation of CH3OOH is more pronounced than that of the unimolecular dissociation of CD3OOD. The isotope effect is more distinct in the anharmonic oscillator model.
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    THEORETICAL STUDIES OF ANHARMONIC EFFECT IN THE RICE RAMSPERGER KASSEL MARCUS THEORY
    (2008-12-20)
    Yao, L.
    ;
    Liu, Y. L.
    ;
    Lin, S. H.
    ;
    應用化學系
    ;
    Department of Applied Chemistry
    The purpose of this paper is to propose a theoretical approach, which can evaluate anharmonic effects on the rate constants within the transition state theory. In treating unimolecular reactions under collision-free conditions by using the RRKM theory, we make use of the inverse Laplace transformation of the partition functions to obtain both the total number of states for the activated complex and density of states for the reactant with the Morse oscillator potential. To demonstrate the applications of our theoretical approach, we choose some model systems and a real reaction as examples.