Chemical Dynamics Simulation Of NH₂ With NO₂

The formation and emission of nitrogen oxides in the atmosphere has always been an environmental issue of great concern,of which the reaction between nitrogen hydride and nitrogen oxide is particularly important.NO₂ radical is an important intermediate in selective non-catalytic reduction（SNCR）process.NH₂ + NO₂ reaction is not only a rapid removal step of NO₂ in thermal denitration,but also the most basic way to generate N-N chain in combustion system,which is very important to the performance of SNCR using amino additives.At the same time,NH₂ radical is an important intermediate in various combustion environments.This reaction is crucial in the combustion of clean and non-corrosive ammonium nitrate propellant.However,at present,the research on the chemical dynamics simulation of NH₂ + NO₂ reaction at home and abroad is still very limited,and the detailed dynamics process,reaction possibility,reaction branching ratio,reaction mechanism and other dynamics properties cannot be deduced.In this paper direct dynamics simulations have been performed for NH₂ + NO₂ reaction to explore the above problems.In this paper,MP2 and seven DFT functionals,including B3 LYP,OPBE,Bhand H,HCTH407,M06,M06-2X combined with aug-cc-pVDZ,were used to calculate the stationary points.CCSD（T）/aug-cc-pVTZ energies were served as the benchmark to calculate the average deviations and relative standard deviations.B3LYP/ aug-cc-pVDZ method was selected as the best method to construct the potential energy surface of NH₂+ NO₂ reaction.There are three product channels for this reaction,namely NH₂ + NO₂ →N2O + H₂O（P1）,NH₂ + NO₂ → H₂NO+NO（P2）and NH₂ + NO₂ → HNO + HNO（P3）.At the early stage,there are two bonding modes.The N atom in the NH₂ group can either interacts with the N atom in the NO₂ group to form an H₂NNO₂ complex,or combines with the O atom in the NO₂ group to form an H₂ NONO complex with new N-O bond.In terms of the PES,it can be seen that the energy of P1 and P2 channels is lower than P3,more stable and easier to form.Moreover,on the basis of previous studies,this paper further improves and explains the PES.Based on the PES and experimental reports,the initial conditions for the simulations in this paper are determined,with the collision energy of 0.89 kcal mol-1.The direct dynamics simulations have been carried out with B3LYP/aug-cc-pVDZ method for NH₂ +NO₂ reaction.The reaction possibility,product branching ratio,and the reaction mechanisms at the atomic level were investigated in detail.Through the statistics of reaction probability and product branching ratio,it was found that at low temperature of298 K,P2 product channel dominated,although in terms of energy,P1 is more exothermic than P2.This conclusion will provide reference for the experimental contradiction inproduct branching ratio measurement.By analyzing the trajectory results,five reaction mechanisms were identified,including four indirect mechanisms which are passing through different complex and one direct mechanism.Among them,indirect reactions play a dominant role.Interestingly,the dynamic evolution process of the generated product trajectory is roughly the same as that of the potential energy surface,and almost completely follows the IRC.Abundant dynamic results have been obtained in the study of NH₂ + NO₂ reaction,which is expected to provide some references for the experiment and further enrich the understanding of this reaction.