Browsing by Author "Lai, Ke-Yu"

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Ab Initio Chemical Kinetics for the Hydrolysis of N2O4 Isomers in the Gas Phase
(2012-05-10)
Zhu, R. S.
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Lai, Ke-Yu
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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 and kinetics for the gas-phase hydrolysis of N2O4 isomers have been investigated at the CCSD (T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p) level of theory in conjunction with statistical rate constant calculations. Calculated results show that the contribution from the commonly assumed redox reaction of sym-N2O4 to the homogeneous gas-phase hydrolysis of NO2 can be unequivocally ruled out due to the high barrier (37.6 kcal/mol) involved; instead, t-ONONO2 directly formed by the association of 2NO(2), was found to play the key role in the hydrolysis process. The kinetics for the hydrolysis reaction, 2NO(2) + H2O <-> HONO + HNO3 (A) can be quatitatively interpreted by the two step mechanism: 2NO(2) -> t-ONONO2, t-ONONO2 + H2O -> HONO + HNO3. The predicted total forward and reverse rate constants for reaction (A), k(tf) = 5.36 x 10(-50)T(3.95) exp(1825/T) cm(6) molecule(-2) s(-1) and k(tr) = 3.31 X 10(-19)T(2.478) exp(-3199/T) cm(3) molecule(-1) s(-1), respectively, in the temperature range 200-2500 K, are in good agreement with the available experimental data.
Why mixtures of hydrazine and dinitrogen tetroxide are hypergolic?
(2012-06-01)
Lai, Ke-Yu
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Zhu, Rongshun
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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 reactions of N2H4 with N2O4 isomers have been investigated at the G2M(CC3)//B3LYP/6311++G(3df,2p) level. The results show that the reactions of N2H4 with sym-N2O4 (D-2h), cis-ONONO2 (C-s), and NO2 have to overcome 14.2, 10.6, and 7.6 kcal/mol barriers, respectively. However, N2H4 can react spontaneously with trans-ONONO2 (C-s) and cis-ONONO2 (C-1) to produce HONO2 + H2NN(H)NO with the near gas-kinetic rate constant, 4 x 10(-10) cm(3) molecule(-1) s(-1) above 250 K. The H2NN( H) NO thus formed can rapidly fragment to give reactive N2H3 radical with rate constant > 1 x 10(7) s(-1) at 1000 K, which is fast enough to initiate the hypergolic chain reactions with NO2 and N2O4. (C) 2012 Elsevier B.V. All rights reserved.