CH3NHNH2 + OH Reaction: Mechanism and Dynamics Studies

A direct dynamics study was carried out for the multichannel reaction of CH3NHNH2 with OH radical. Two stable Conformers (I, II) of CH3NHNH2 are identified by the rotation of the -CH3 group. For each conformer, five hydrogen-abstraction channels are found. The reaction mechanisms of product radicals (CH3NNH2 and CH3NHNH) with OH radical are also investigated theoretically. The electronic structure information on the potential energy surface is obtained at the B3LYP/6-311G(d,p) level and the energetics along the reaction path is refined by the BMC-CCSD method. Hydrogen-bonded complexes are presented at both the reactant and product sides of the five channels, indicating that the reaction may proceed via all indirect mechanism. The influence of the basis set superposition error (BSSE) on the energies of all the complexes is discussed by means of the CBS-QB3 method. The rate constants of CH3NHNH2 + OH are calculated using canonical variational transition-state theory with the small-curvature tunneling correction (CVT/SCT) in the temperature range of 200-1000 K. Slightly negative temperature dependence of rate constant is found in the temperature range from 200 to 345 K. The agreement between the theoretical and experimental results is good. It is shown that for Conformer I. hydrogen-abstraction front -NH- position is the primary pathway at low temperature: the hydrogen-abstraction from -NH2 is a competitive pathway as the temperature increases. A similar case call be concluded for Conformer II. The overall rate constant is evaluated by considering, the weight factors of each conformer from the Boltzmann distribution function, and the three-term Arrhenius expressions are fitted to be k(T) = 1.6 x 10(-24)T(4.03) (1411.5/T) cm(3) molecule(-1) s(-1) between 200-1000 K. (C) 2009 Wiley Periodicals. Inc. J Comput Chem 30: 2194-2204. 2009