Browsing by Author "Zhu, Rongshun"

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Roaming-mediated isomerization in the photodissociation of nitrobenzene
(2011-12-01)
Hause, Michael L.
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Herath, Nuradhika
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Zhu, Rongshun
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Lin, M. C.
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Suits, Arthur G.
Roaming reactions comprise a new class of reaction in which a molecule undergoes frustrated dissociation to radicals, followed by an intramolecular abstraction reaction. Nitro compounds have long been known to dissociate to give NO as a major product. However, rates based upon isomerization via calculated tight transition states are implausibly slow, so the key dissociation pathway for this important class of molecules remains obscure. Here, we present an imaging study of the photodissociation of nitrobenzene with state-specific detection of the resulting NO products. We observe a bimodal translational energy distribution in which the slow products are formed with low NO rotational excitation, and the fast component is associated with high rotational excitation. High-level ab initio calculations identified a 'roaming-type' saddle point on the ground state. Branching ratio calculations then show that thermal dissociation of nitrobenzene is dominated by 'roaming-mediated isomerization' to phenyl nitrite, which subsequently decomposes to give C(6)H(5)O+NO.
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.