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    Anharmonic effect of the unimolecular dissociation of CH3COOH
    (2014-11-02)
    Zhang, Liwei
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    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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    The anharmonic effect study of coupled Morse oscillators for the unimolecular reaction
    (2008-12-01)
    Yao Li
    ;
    Lin Sheng-Hsien
    ;
    應用化學系
    ;
    應用化學系分子科學碩博班
    ;
    Department of Applied Chemistry
    The importance of anharmonic effect in dissociation of molecular systems especially clusters has been noted. In this paper, we shall study the effect of coupled anharmonic oscillator of the standard bilinear form (SBF) Morse oscillator (MO) potential on unimolecular reaction. We shall use the systematic theoretical approach, YL method, proposed by Yao and Lin (YAO L, et. al. J Phys Chem A, 2007, 111( 29): 6722-6729), which can evaluate anharmonic effects on the rate constants based on the transition state theory. In treating the anharmonic effect with the Morse oscillator potential on unimolecular reactions under collision-free conditions by using the RRKM (Rice-Ramsperger-Kassel-Marcus) theory, the inverse Laplace transformation of the partition functions was used to obtain the total amount of state and density of state by using the first-order and the second-order approximations of the saddle-point method. To demonstrate the anharmonic effect of the SBF Morse model, we choose some model systems and a real reaction as examples.
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    Ab Initio Chemical Kinetics for Reactions of H Atoms with SiHx (x=1-3) Radicals and Related Unimolecular Decomposition Processes
    (2013-06-15)
    Raghunath, Putikam
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    Lee, Yun-Min
    ;
    Wu, Shang-Ying
    ;
    Wu, Jong-Shinn
    ;
    Lin, Ming-Chang
    Hydrogen atoms and SiHx (x = 1-3) radicals coexist during the chemical vapor deposition (CVD) of hydrogenated amorphous silicon (a-Si: H) thin films for Si-solar cell fabrication, a technology necessitated recently by the need for energy and material conservation. The kinetics and mechanisms for H-atom reactions with SiHx radicals and the thermal decomposition of their intermediates have been investigated by using a high high-level ab initio molecular-orbital CCSD (Coupled Cluster with Single and Double)(T)/CBS (complete basis set extrapolation) method. These reactions occurring primarily by association producing excited intermediates, (SiH2)-Si-1, (SiH2)-Si-3, SiH3, and SiH4, with no intrinsic barriers were computed to have 75.6, 55.0, 68.5, and 90.2 kcal/mol association energies for x = 1-3, respectively, based on the computed heats of formation of these radicals. The excited intermediates can further fragment by H-2 elimination with 62.5, 44.3, 47.5, and 56.7 kcal/mol barriers giving Si-1, Si-3, SiH, and (SiH2)-Si-1 from the above respective intermediates. The predicted heats of reaction and enthalpies of formation of the radicals at 0 K, including the latter evaluated by the isodesmic reactions, SiHx + CH4 SiH4 + CHx, are in good agreement with available experimental data within reported errors. Furthermore, the rate constants for the forward and unimolecular reactions have been predicted with tunneling corrections using transition state theory (for direct abstraction) and variational Rice-Ramsperger-Kassel-Marcus theory (for association/decomposition) by solving the master equation covering the P, T-conditions commonly employed used in industrial CVD processes. The predicted results compare well experimental and/or computational data available in the literature. (C) 2013 Wiley Periodicals, Inc.