Browsing by Author "Yao, L."

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Anharmonic effect on unimolecular reactions with application to the photodissociation of ethylene
(2007-07-26)
Yao, L.
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Mebel, A. M.
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Lu, H. F.
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Neusser, H. J.
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Lin, S. H.
The importance of anharmonic effect on dissociation of molecular systems, especially clusters, has been noted. In this paper, we shall present a theoretical approach that can carry out the first principle calculations of anharmonic canonical and microcanonical rate constants of unimolecular reactions within the framework of transition state theory. In the canonical case, it is essential to calculate the partition function of anharmonic oscillators; for convenience, the Morse oscillator potential will be used for demonstration in this paper. In the microcanical case, which involves the calculation of the total number of states for the activated complex and the density of states for the reactant, we make use of the fact that both the total number of states and the density of states can be expressed in the inverse Laplace transformation of the partition functions and that the inverse Laplace transformation can in turn be carried out by using the saddle-point method. We shall also show that using the theoretical approach presented in this paper the total number of states and density of states can be determined from thermodynamic properties and the difference between the method used in this paper and the thermodynamic model used by Krems and Nordholm will be given. To demonstrate the application of our theoretical approach, we chose the photodissociation of ethylene at 157 and 193 nm as an example.
Dissociation Rate Constant of the Hydrogen Fluoride Dimer by the ab Initio Anharmonic RRKM Theory
(2009-12-31)
Yao, L.
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Mebel, A. M.
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Lin, S. H.
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應用化學系
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Department of Applied Chemistry
The dissociation rate constants for hydrogen fluoride dimers; are calculated using the YL method, proposed by Yao and Lin (Yao, L.; Mebel, A. M.; Lu, H. F.; Neusser, H. J.; Lin, S. H. J.. Phys. Chem. A 2007, 111, 6722). The dividing surface method and RRKM theory are also used to obtain pseudo-transition states and rate constants, respectively. For the dissociation of HF dimers, the anharmonic rate constants are around 3.02 x 10(10) to 3.46 x 10(12) s(-1), while the harmonic rate constants are in the range of 2.93 x 10(10) to 1.66 x 10(13) s(-1), at a temperature range of 243-1000 K, for the canonical case. For the microcanonical case, the anharmonic rate constants are in the range of 1.91 x 10(12) to 1.32 x 10(13) s(-1) and the harmonic rate constants are in the range of 1.89 x 10(12) to 4.93 x 10(13) s(-1), with a total energy range of 1338-4500 cm(-1). Both harmonic and anharmonic rate constants are only comparable to the experimental results 0.5 x 10(10) s(-1) and 1 x 10(11) s(-1) in an inert gas bath at room temperature. In this case the harmonic and anharmonic rate constants show similar results in this calculation. The results of this paper indicate that the YL method is suitable for calculating dissociation rate constants of small flexible HF dimers and the anharmonic effect should be included.
On the calculation of the dissociation rate constant of the water dimer by the ab initio anharmonic RRKM theory
(2009-03-05)
Yao, L.
;
He, R. X.
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Mebel, A. M.
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Lin, S. H.
;
應用化學系
The dissociation rate constant of the water dimer was calculated by using the method proposed by Yao and Lin (YL method). The dividing surface method and RRKM theory are used to calculate the pseudo transition state and the rate constant, respectively. For the canonical case at temperature range of 243-1000 K and for the microcanonical system at total energy 1411-4000 cm(1), the anharmonic rate constant, around 10(9)-10(11) s(1), is close to the experimental prediction. The present results indicate that the anharmonic effect should be included and YL method is suitable for calculating dissociation rate constants of such small flexible water cluster. (C) 2009 Elsevier B. V. All rights reserved.
THEORETICAL STUDIES OF ANHARMONIC EFFECT IN THE RICE RAMSPERGER KASSEL MARCUS THEORY
(2008-12-20)
Yao, L.
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Liu, Y. L.
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Lin, S. H.
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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.