Theoretical Study On The Role Of The Hydrazine And Mono-methylhydrazine In The Hydrolysis Reaction Of NO₂

In air pollution chemistry,nitric acid aerosols are typical secondary pollutants,mainly containing nitrogen oxides?NOX?and nitrous acid?HONO?.Nitrous acid is considered to be an important trace gas in the troposphere,which can be rapidly decomposed by light to release a large amount of OH radicals.The source of nitrous acid and the chemical mechanism of its formation have not been well understood and recognized,although its importance has been recognized.In this paper,the effects of hydrazine and mono-methylhydrazine on the hydrolysis of nitrogen dioxide were studied,and compared with ammonia and methylamine.The structure,energy and thermodynamic changes of the two molecular clusters 2NO₂-mH₂O-N₂H₄?m=1-3?,2NO₂-mH₂O-CH₃NHNH₂?m=1,2?were calculated by quantum chemical theory.The specific reaction process is as follows:2NO₂+mH₂O+N₂H₄?N₂H₄·HNO₃/N₂H₅⁺NO₃^-+HONO?m=1-3?2NO₂+mH₂O+CH₃NHNH₂?CH₃NHNH₂·HNO₃/CH₃NHNH₃⁺NO₃^-+HONO?m=1,2?The results show that hydrazine and methyl hydrazine can be used as a catalyst to effectively promote the NO₂ hydrolysis reaction.Compared with methylamine and ammonia,the reaction is more exothermic and the ability to stabilize the complex is stronger.The energy barrier of the hydrazine-promoted hydrolysis reaction?1.99 kcal/mol?was significantly lower than that of the bare reaction?11.47 kcal/mol?;When monomethylhydrazine is used as a catalyst,the reaction energy barrier is further reduced to 0.54 kcal/mol.During the hydrolysis reaction of m=1,hydrazine and monomethyl hydrazine form the N₂H₄-HNO₃ and CH₃NHNH₂-HNO₃ acid-base complex structures and release HONO as a source of atmospheric aerosol precursors.As the humidity increases,additional water molecules?m=2,3?can act as solvents or reactants to stabilize the relative energy of the transition state and product complex and reduce the energy barrier of the reaction.The zwitterionic structures N₂H₄⁺NO₃^-?HDN?and CH₃NHNH₃⁺NO₃^-?MMHN?are more readily formed in reactions involving multiple water molecules.The donor-acceptor hydrogen bond interaction between hydrazine/monomethylhydrazine and nitric acid was analyzed by the natural bond orbital?NBO?method.The hydrogen bond interaction between monomethyl hydrazine and nitric acid is stronger than the corresponding hydrazine and methylamine.The thermodynamics of the corresponding reactions have significant advantages.The reactions involving the diamines system are more spontaneous than the monoamines and tend to form zwitterionic structures.