TY - GEN
T1 - Kinetics Study of Reaction CH3N•hNH2 + OH by multireference second-order perturbation theory and multireference coupled-cluster theory
AU - Sun, Hongyan
AU - Law, Chung K.
AU - Kowalski, Karol
AU - Bhaskaran-Nair, Kiran
PY - 2013
Y1 - 2013
N2 - The H-abstraction reactions of monomethylhydrazine (MMH) generate four radical intermediates: CH3N•ENH2, cis-CH3NHN•EH, trans-CH3NHN•EH, and C•EH2NHNH2, which undergo further decomposition to smaller radicals and stable products. The s-scission of H atom from the CH3N•ENH2 radical is not as feasible as the s-scission of NH2 and CH3 radicals from the other three radicals due to its higher energy barrier (Sun et al., J. Phys. Chem. A, 2012, 116(33), 8419-8430). Consequently, the CH3N•ENH2 radical undergoes further oxidation reactions. Due to the strong quasi-degeneracy effect, the kinetics of CH3N•ENH2 + OH was studied in detail with application of several ab initio quantum chemistry theories. Twenty-five geometries of the stationary point of potential energy surface were investigated by using multi-reference second-order perturbation theory. The single point energies were refined by quadratic configuration interaction theory, coupled-cluster theory, locally renormalized coupled-cluster theory, and state selective multi-reference coupled-cluster theory including Brillouin-Wigner and Mukherjee•'s approaches, with single and double excitations and correction for triple excitations. For the OH addition to the central and terminal nitrogen of the CH3N•ENH2 radical, the state-averaged active space (4e,3o) consists of two degenerated p orbitals of the OH and the p orbitals of N atoms in the transition states and H-bonded complexes. For the dissociation of the CH3N(OH)NH2 and CH3NNH2(OH) adducts, a larger active space was applied. Specifically, for the OH intramolecular abstraction of methyl H, the active space consists of 10 electrons distributed in 8 orbitals: σ and π bonding and antibonding pairs of N'{N bond, σ bonding and antibonding pair of O'{H bond, the π bonding of N'{O bond, and the s orbital of central nitrogen. The predominant channel was found to be the OH addition to terminal N atom of CH3N•ENH2 with submerged energy barriers via two optical isomeric H-bonded complexes with energy of -5.73 kcal/mol; the forming CH3NNH2OH adduct decomposes via small energy barrier to trans- and cis-methyldiazene and water with exothermicity up to 75 kcal/mol. The large exothermicity and negative energy barrier of the reaction implicate its significant importance in MMH earlier ignition.
AB - The H-abstraction reactions of monomethylhydrazine (MMH) generate four radical intermediates: CH3N•ENH2, cis-CH3NHN•EH, trans-CH3NHN•EH, and C•EH2NHNH2, which undergo further decomposition to smaller radicals and stable products. The s-scission of H atom from the CH3N•ENH2 radical is not as feasible as the s-scission of NH2 and CH3 radicals from the other three radicals due to its higher energy barrier (Sun et al., J. Phys. Chem. A, 2012, 116(33), 8419-8430). Consequently, the CH3N•ENH2 radical undergoes further oxidation reactions. Due to the strong quasi-degeneracy effect, the kinetics of CH3N•ENH2 + OH was studied in detail with application of several ab initio quantum chemistry theories. Twenty-five geometries of the stationary point of potential energy surface were investigated by using multi-reference second-order perturbation theory. The single point energies were refined by quadratic configuration interaction theory, coupled-cluster theory, locally renormalized coupled-cluster theory, and state selective multi-reference coupled-cluster theory including Brillouin-Wigner and Mukherjee•'s approaches, with single and double excitations and correction for triple excitations. For the OH addition to the central and terminal nitrogen of the CH3N•ENH2 radical, the state-averaged active space (4e,3o) consists of two degenerated p orbitals of the OH and the p orbitals of N atoms in the transition states and H-bonded complexes. For the dissociation of the CH3N(OH)NH2 and CH3NNH2(OH) adducts, a larger active space was applied. Specifically, for the OH intramolecular abstraction of methyl H, the active space consists of 10 electrons distributed in 8 orbitals: σ and π bonding and antibonding pairs of N'{N bond, σ bonding and antibonding pair of O'{H bond, the π bonding of N'{O bond, and the s orbital of central nitrogen. The predominant channel was found to be the OH addition to terminal N atom of CH3N•ENH2 with submerged energy barriers via two optical isomeric H-bonded complexes with energy of -5.73 kcal/mol; the forming CH3NNH2OH adduct decomposes via small energy barrier to trans- and cis-methyldiazene and water with exothermicity up to 75 kcal/mol. The large exothermicity and negative energy barrier of the reaction implicate its significant importance in MMH earlier ignition.
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M3 - Conference contribution
AN - SCOPUS:84943397901
T3 - 8th US National Combustion Meeting 2013
SP - 1763
EP - 1767
BT - 8th US National Combustion Meeting 2013
PB - Western States Section/Combustion Institute
T2 - 8th US National Combustion Meeting 2013
Y2 - 19 May 2013 through 22 May 2013
ER -