Browsing by Author "Chen, Hui-Lung"

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Ab Initio Chemical Kinetics for H plus NCN: Prediction of NCN Heat of Formation and Reaction Product Branching via Doublet and Quartet Surfaces
(2013-07-18)
Teng, Wen-Shuang
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Moskaleva, Lyudmila V.
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Chen, Hui-Lung
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Lin, M. C.
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應用化學系
The reaction of NCN with H atoms has been investigated by ab initio MO and RRKM theory calculations. The mechanisms for formation of major products on the doublet and quartet potential energy surfaces have been predicted at the CCSD(T) level of theory with the complete basis set limit. In addition, the heat of formation for NCN predicted at this rigorous level and those from five isogyric reactions are in close agreement with the best value based on the isodesmic process, (CCO)-C-3 + N-2 = (NCN)-N-3 + CO, 109.4 kcal/mol, which lies within the two existing experimental values. The rate constants for the three possible reaction channels, H + NCN -> CH + N-2 (k(P1)), HCN + N-4 (k(QP1)), and HNC + N-4 (k(QP2)), have been calculated in the temperature range 298-3000 K. The results show that k(P1) is significantly higher than k(QP1) and k(QP2) and that the total rate constant agrees well with available experimental values in the whole temperature range studied. The kinetics of the reverse CH + N-2 reaction has also been revisited at the CCSD(T)/CBS level; the predicted total rate constants at 760 Torr Ar pressure can be represented by k(r) = 4.01 x 10(-15) T-0.90 exp(-17.42 kcal mol(-1)/RT) cm(3) molecule(-1) s(-1) at T = 800-4000 K. The result agrees closely with the most recent experimental data and the best theoretical result of Harding et al. (J. Phys. Chem. A 2008, 112, 522) as well as that of Moskaleva and Lin (Proc. Combust. Inst. 2000, 28, 2393) evaluated with a steady-state approximation after a coding error correction made in this study.
Adsorption and dissociation of the HCl and Cl-2 molecules on W(111) surface: A computational study
(2008-08-14)
Chen, Hui-Lung
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Ju, Shin-Pon
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Chen, Hsin-Tsung
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Musaev, Djamaladdin G.
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Lin, M. C.
The adsorption and dissociation of Cl-2 and HCl molecules on W(111) surface have been studied at the density functional theory (DFT) level in conjunction with the projector augmented wave (PAW) method. The molecular structures and surface-adsorbent interaction energies of W(111)/Cl, W(111)/H, W(111)/Cl-2, and W(111)/HCl systems are predicted. In these studies, four adsorption sites, such as top (T), bridge (B), shallow (S), and deep (D) sites, of the W(111) surface are considered. It is shown that the Cl-2 and HCl molecules adsorb to the W(111) surface by the end-on manner (by their Cl-Cl or H-Cl bonds perpendicular to the W surface), and their dissociative adsorptions occur without intrinsic energy barriers and are exothermic by 80.46 and 53.72 kcal/mol, for Cl-2 and HCl, respectively. Molecular dynamics studies show that the dissociation of Cl-2 and HCl molecules on the W(111) surface occur in asymmetric fashion: at the beginning adsorbate forms a strong bond between one of their atoms and W centers, followed by the dissociation of the Cl-Cl (and/or H-Cl) bond and formation of the second bond between the atoms of adsorbate and the W center. For the Cl-2 molecule, both Cl atoms are preferred to adsorb at the top W centers. For the HCl molecule, after the dissociation of the H-Cl bond the Cl atom still occupies the top adsorption site, but the H atom prefers to move to the position between the top and shallow W centers. The rate constants for the dissociative adsorption of Cl-2 and HCl have been predicted with variational RRKM theory.
Density Functional Studies of the Adsorption and Dissociation of NO(x) (x=1, 2) Molecules on the W(111) Surface
(2009-04-02)
Chen, Hsin-Tsung
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Chen, Hui-Lung
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Ju, Shin-Pon
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Musaev, Djamaladdin G.
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Lin, M. C.
Adsorption and dissociation of NOx (x = 1, 2) molecules on the W(111) surface have been investigated by using the density functional theory (DFT) with the projector-augmentcd wave (PAW) approach in periodic boundary conditions. The adsorption structures, vibrational frequencies, and binding energies of NO(2), NO, N, and 0 on the W(111) surface were predicted. It was shown that the most favorable adsorption geometry of W(111)/NO(2) is the WNO(2) (IV-mu(3)-N2, OI, OI) configuration with NO(2) at the 3-fold-shallow site of the surface and has an adsorption energy of 79.4 kcal/mol. For W(111)NO, WNO(II-mu(2)-N1, O1) with NO at the bridge site is energetically the most favorable one and has an adsorption energy of 74.4 kcal/mol. The N and 0 atoms are bound preferentially at the bridge and top sites, respectively. The potential energy profiles for the decomposition of NO(2) on W(111) were constructed using the nudged elastic band (NEB) method. The barriers for the stepwise NO(2)-deoxygenation process to N((ads)) + 20((ads)) are calculated to be only 0.5-3.7 (for the first step of the reaction, ON-O bond activation) and 0.2-3.0 (for the second step of the reaction, N-O bond activation of the coordinated NO molecule) kcal/mol, with an overall exothermicity of 177.0-185.2 kcal/mol. These findings show that NO,) can easily decompose on the W(111) surface. The rate constants for NO(2) and NO dissociation on the surface were also predicted.
Density Functional Studies of the Adsorption and Dissociation of NOx (x=1, 2) Molecules on the W(111) Surface
(2009-04-02)
Chen, Hsin-Tsung
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Chen, Hui-Lung
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Ju, Shin-Pon
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Musaev, Djamaladdin G.
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Lin, M. C.
Adsorption and dissociation of NOx (x = 1, 2) molecules on the W(111) surface have been investigated by using the density functional theory (DFT) with the projector-augmentcd wave (PAW) approach in periodic boundary conditions. The adsorption structures, vibrational frequencies, and binding energies of NO2, NO, N, and 0 on the W(111) surface were predicted. It was shown that the most favorable adsorption geometry of W(111)/NO2 is the WNO2 (IV-mu(3)-N2, OI, OI) configuration with NO2 at the 3-fold-shallow site of the surface and has an adsorption energy of 79.4 kcal/mol. For W(111)NO, WNO(II-mu(2)-N1, O1) with NO at the bridge site is energetically the most favorable one and has an adsorption energy of 74.4 kcal/mol. The N and 0 atoms are bound preferentially at the bridge and top sites, respectively. The potential energy profiles for the decomposition of NO2 on W(111) were constructed using the nudged elastic band (NEB) method. The barriers for the stepwise NO2-deoxygenation process to N-(ads) + 20((ads)) are calculated to be only 0.5-3.7 (for the first step of the reaction, ON-O bond activation) and 0.2-3.0 (for the second step of the reaction, N-O bond activation of the coordinated NO molecule) kcal/mol, with an overall exothermicity of 177.0-185.2 kcal/mol. These findings show that NO,) can easily decompose on the W(111) surface. The rate constants for NO2 and NO dissociation on the surface were also predicted.
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.
Quantum Chemical Prediction of Reaction Pathways and Rate Constants for the Reactions of O-x (x=1 and 2) with Pristine and Defective Graphite (0001) Surfaces
(2012-01-19)
Xu, S. C.
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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
We present reaction pathways for adsorption reactions of the O atom and O-2 molecule in the pristine and monovacancy defective graphite (0001) based on quantum chemical potential energy surfaces (PESs) obtained by the dispersion-augmented density-functional tight-binding (DFTB-D) method. We use a dicircumcoronene C96H24 (L0D) graphene slab as the pristine graphite (0001) model and dicircumcoronene C95H24 (LIV) as the graphite (0001) monovacancy defect model. We found that the adsorption reactions of O and O-2 on the L0D surface can produce defects on the graphite surface. O can yield CO, while O-2 can yield both CO and CO2 molecules. The adsorption reactions of the O and O-2 on the LW surface can produce a 2-C defective graphite surface and CO, and CO and CO2, respectively. The O and O-2 more readily oxidize the defected surface, LIV, than the defect-free surface, L0D. On the basis of the computed reaction pathways, we predict reaction rate constants in the temperature range between 300 and 3000 K using Rice-Ramsperger-Kassel-Marcus (RRKM) theory. High-temperature quantum chemical molecular dynamics simulations at 3000 K based on on-the-fly DFTB-D energies and gradients support the results of our PES studies.