Browsing by Author "Nguyen, Hue M. T."

Now showing 1 - 4 of 4

Dynamics of the reactions of O(D-1) with CD3OH and CH3OD studied with time-resolved Fourier-transform IR spectroscopy
(2012-10-28)
Huang, Chong-Kai
;
Xu, Zhen-Feng
;
Nakajima, Masakazu
;
Nguyen, Hue M. T.
;
Lin, M. C.
We investigated the reactivity of O(D-1) towards two types of hydrogen atoms in CH3OH. The reaction was initiated on irradiation of a flowing mixture of O-3 and CD3OH or CH3OD at 248 nm. Relative vibration-rotational populations of OH and OD (1 <= nu <= 4) states were determined from their infrared emission recorded with a step-scan time-resolved Fourier-transform spectrometer. In O(D-1) + CD3OH, the rotational distribution of OD is nearly Boltzmann, whereas that of OH is bimodal; the product ratio [OH]/[OD] is 1.56 +/- 0.36. In O(D-1) + CH3OD, the rotational distribution of OH is nearly Boltzmann, whereas that of OD is bimodal; the product ratio [OH]/[OD] is 0.59 +/- 0.14. Quantum-chemical calculations of the potential energy and microcanonical rate coefficients of various channels indicate that the abstraction channels are unimportant and O(D-1) inserts into the C-H and O-H bonds of CH3OH to form HOCH2OH and CH3OOH, respectively. The observed three channels of OH are consistent with those produced via decomposition of the newly formed OH or the original OH moiety in HOCH2OH or decomposition of CH3OOH. The former decomposition channel of HOCH2OH produces vibrationally more excited OH because of incomplete intramolecular vibrational relaxation, and decomposition of CH3COOH produces OH with greater rotational excitation, likely due to a large torque angle during dissociation. The predicted [OH]/[OD] ratios are 1.31 and 0.61 for O(D-1) + CD3OH and CH3OD, respectively, at collision energy of 26 kJ mol(-1), in satisfactory agreement with the experimental results. These predicted product ratios vary weakly with collision energy. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4759619]
Mechanisms for reactions of trimethylaluminum with molecular oxygen and water
(2014-05-01)
Nguyen, Hue M. T.
;
Tang, Hsin-Yu
;
Huang, Wen-Fei
;
Lin, M. C.
;
應用化學系
(CH3)(3)Al(TMA) has been employed for preparation of various thin films. It is also known to be hypergolic in the air. To unveil the hypergolic phenomenon, the mechanism for the reaction of TMA with O-2 and/or H2O molecules is studied using computational quantum methods. Our results show that TMA reacts with water much faster than with O-2, and water is not an efficient catalyst to help O-2 reacting with TMA. The reactions of TMA with water and oxygen molecules can undergo subsequent ones in the air. However, the barrier predicted for production of CH3 was found to be too high for combustion initiation under the ambient condition. (c) 2014 Elsevier B.V. All rights reserved.
On the hypergolicity of trimethyl aluminum in air
(2020-03-01)
Pham, Tien, V
;
Nguyen, Hue M. T.
;
Lin, M. C.
;
交大名義發表
;
應用化學系
A theoretical study on the mechanisms and kinetics of the reaction of (CH3)(3)Al (TMA), an important industrial compound, with O-2 has been carried out at the CCSD(T)/6-311 + +G(3df,2p)//B3LYP/6-311 + + G(3df,2p) level in conjunction with the conventional transition state theory (TST) calculations. The potential energy surface (PES) of the reaction indicates that the TMA + O-2 system has two pathways leading to different product pairs: the first one passes through a tight transition state with a high energy barrier, 16.9 kcal/mol, producing (CH3)(2)AlO2 + CH3 and the other one goes via a loose roaming-like transition state with a much lower energy barrier, 6.8 kcal/mol, yielding CH3Al(O)OCH3 + CH3. The barrier predicted for the former was found to be too high for combustion initiation under the ambient condition. The latter, however, may play a key role in initiating the hypergolic reaction of TMA in the air. Rate constants for both channels have been calculated for the temperature range of 300-2000 K. The pressure-independent rate constant for the TMA + O-2 reaction via the loose transition state is predicted to be k(T) = 3.05 x 10(-21)T(3.003) exp( - 3226.1/T) cm(3) molecule(-1) s(-1); this result gives the half-life of TMA in air under the ambient condition to be as short as 1.7 x 10(-2) s, which is sufficiently short for the hypergolic combustion initiation without even considering the ensuing rapid radical chain reactions.
Reaction dynamics of O(D-1) + HCOOD/DCOOH investigated with time-resolved Fourier-transform infrared emission spectroscopy
(2014-10-21)
Huang, Shang-Chen
;
Nghia, N. T.
;
Putikam, Raghunath
;
Nguyen, Hue M. T.
;
Lin, M. C.
We investigated the reaction dynamics of O(D-1) towards hydrogen atoms of two types in HCOOH. The reaction was initiated on irradiation of a flowing mixture of O-3 and HCOOD or DCOOH at 248 nm. The relative vibration-rotational populations of OH and OD (1 <= upsilon <= 4, J <= 15) states were determined from time-resolved IR emission recorded with a step-scan Fourier-transform spectrometer. In the reaction of O(D-1) + HCOOD, the rotational distribution of product OH is nearly Boltzmann, whereas that of OD is bimodal. The product ratio [OH]/[OD] is 0.16 +/- 0.05. In the reaction of O(D-1) + DCOOH, the rotational distribution of product OH is bimodal, but the observed OD lines are too weak to provide reliable intensities. The three observed OH/OD channels agree with three major channels of production predicted with quantum-chemical calculations. In the case of O(D-1) + HCOOD, two intermediates HOC(O)OD and HC(O)OOD are produced in the initial C-H and O-D insertion, respectively. The former undergoes further decomposition of the newly formed OH or the original OD, whereas the latter produces OD via direct decomposition. Decomposition of HOC(O)OD produced OH and OD with similar vibrational excitation, indicating efficient intramolecular vibrational relaxation, IVR. Decomposition of HC(O)OOD produced OD with greater rotational excitation. The predicted [OH]/[OD] ratio is 0.20 for O(D-1) + HCOOD and 4.08 for O(D-1) + DCOOH; the former agrees satisfactorily with experiments. We also observed the upsilon(3) emission from the product CO2. This emission band is deconvoluted into two components corresponding to internal energies E = 317 and 96 kJ mol(-1) of CO2, predicted to be produced via direct dehydration of HOC(O)OH and secondary decomposition of HC(O)O that was produced via decomposition of HC(O)OOH, respectively. (C) 2014 AIP Publishing LLC.