Browsing by Author "Trong-Nghia Nguyen"

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A novel and facile decay path of Criegee intermediates by intramolecular insertion reactions via roaming transition states
(2015-03-28)
Trong-Nghia Nguyen
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Putikam, Raghunath
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Lin, M. C.
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應用化學系
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應用化學系分子科學碩博班
We have discovered a new and highly competitive product channel in the unimolecular decay process for small Criegee intermediates, CH2OO and anti/syn-CH3C(H)OO, occurring by intramolecular insertion reactions via a roaming-like transition state (TS) based on quantum-chemical calculations. Our results show that in the decomposition of CH2OO and anti-CH3C(H)OO, the predominant paths directly produce cis-HC(O)OH and syn-CH3C(O)OH acids with >110 kcal/mol exothermicities via loose roaming-like insertion TSs involving the terminal O atom and the neighboring C-H bonds. For syn-CH3C(H)OO, the major decomposition channel occurs by abstraction of a H atom from the CH3 group by the terminal O atom producing CH2C(H)O-OH. At 298 K, the intramolecular insertion process in CH2OO was found to be 600 times faster than the commonly assumed ring-closing reaction. (c) 2015 AIP Publishing LLC.
Ab Initio Chemical Kinetics for SiHx Reactions with Si2Hy (x=1,2,3,4; y=6,5,4,3; x plus y=7) under a-Si:H CVD Condition
(2017-03-01)
Trong-Nghia Nguyen
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Lin, M. C.
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應用化學系
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Department of Applied Chemistry
Gas-phase reactions of SiHx with Si2Hy (x = 1,2,3,4; y = 6,5,4,3) species, respectively, which may coexist under chemical vapor deposition (CVD) conditions, have been investigated by means of ab initio molecular orbital and statistical theory calculations. Potential energy surface (PES) predicted at the CCSD(T)/CBS//B3LYP/6-311++G(3df,2p) level shows that these reactions take place primarily via trisilany radicals, n-Si3H7 and i-Si3H7. For example, SiH2 can associate with Si2H5 producing n-H2SiSiH2SiH3 exothermically by 55.8 kcal/mol; SiH3 can undergo addition to H2SiSiH2 to produce n-Si3H7 or associate with H3SiSiH barrierlessly forming i-Si3H7; whereas SiH can insert into one of the SiH bonds of Si2H6 to give excited n-Si3H7. Similarly, H2SiSiH and SiSiH3 can undergo insertion reactions with SiH4 producing n/i-Si3H7 intermediates, respectively, to be followed by fragmentation to various smaller species. These processes are fully depicted in the complete PES. The predicted heats of formation of various species agree well with available thermochemical data. The rate constants and product branching ratios for the low-energy channel products have been calculated for the temperature range 300-1000 K by variational RRKM (Rice-Ramsperger-Kassel-Macus) theory with Eckart tunneling corrections. The results may be employed for realistic kinetic modeling of the plasma-enhanced chemical vapor deposition growth of a-Si:H thin films under practical conditions. (C) 2017 Wiley Periodicals, Inc.
Capturing H and H-2 by SiHx+ (x <= 4) ions: Comparison between Langevin and quantum statistical models
(2017-02)
Trong-Nghia Nguyen
;
Lee, Yun-Min
;
Wu, Jong-Shinn
;
Lin, Ming-Chang
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機械工程學系
H, H-2, and SiHx+ (x <= 4) ions coexist under plasma-enhanced chemical vapor deposition (PECVD) conditions. We have studied the kinetics of their interactions by high-level quantum chemical and statistical theory calculations, and compared the results with classical Langevin values (similar to 2 x 10(-9)cm(3) molecule(-1) s(-1) independent of temperature). The results indicate that, for H capturing by SiHx+ (x <= 4), both theories agree within a factor of 2-4, whereas for H-2 capturing by SiHx+ (x <= 3), the modern theory gives higher and weakly temperature-dependent values by up to more than one order of magnitude, attributable to reaction path degeneracies and increased entropies of activation. The heats of formation and structural parameters of SiHx+ ions (x <= 5) in this work agree well with available experimental data. For practical applications, we have provided tables of rate constants for modeling various processes of relevance to the PECVD of a-Si: H films. (C) 2017 The Japan Society of Applied Physics