Branching Ratios of Aliphatic Amines + OH Gas-Phase Reactions: A Variational Transition-State Theory Study.

A theoretical study on the mechanism of the OH + aliphatic amines reactions is presented. Geometry optimization and frequencies calculations have been performed at the BHandHLYP/6-311++G(2d,2p) level of theory for all stationary points. Energy values have been improved by single-point calculations at the above geometries using CCSD(T) and the same basis set. All the possible hydrogen abstraction channels have been modeled, involving the rupture of C-H and N-H bonds. It was found that as the temperature decreases the contributions of the channels involving NH sites to the overall reaction also decrease, suggesting that for upper layers in the troposphere these channels become less important. Their percentage contributions to the overall reaction, at 298 K, were found to be about 20%, 2%, and 48% for methylamine, ethlylamine, and dimethylamine, respectively.