Study On Anharmonic Effect Of Cracking Of Two Intermediates In Combustion Process Of Monomethylhydrazine

It is well known that the launch of spacecraft requires power provided by the combustion of a large amount of fuel.Additionally,monomethylhydrazine(MMH),which is utilized as space fuel,is usually combined with oxidant,such as nitrous(NTO)or red fuming nitric(RFNA),to be utilized as one type of widespread two-component liquid propellant.Furthermore,cis-CH3NHNH and CH3NHNHNO2,which are generated as intermediates in the combustion process,play a vital role in the whole reaction.Hence,it is the theoretical calculation of the cracking of these two intermediates that is an important part of the research on the combustion processes.In this present work,on the basis of the Transition State Theory(TST)and Rice Ramsperger Kassel Marcus(RRKM)theory,we employ the software of GaussView 5.0 and Gaussian 09 in order to optimize the structures of reactants and transition states involving in the cracking of cis-CH3NHNH and CH3NHNHNO2.Moreover,based on the energy barriers modified and frequencies calculated,this paper calculates rate constants by means of Yao-Lin(YL)method.Besides,according to the rate constants obtained,we make an analysis of the anharmonic effect.Finally,in the light of the Arrhenius equation and the least square method,we get the fitting results of the three parameters of Arrhenius equation,namely A,n,E,in order to lay the foundation for the follow-up theoretical studies.Concerning the first reaction system,namely the cracking of cis-CH3NHNH,we obtain a total of 20 transition states,which involves in the process of cis-CH3NHNH transforming into the other three intermediates and the cracking of these four intermediates,by using MP2 and B3LYP method.Moreover,we obtain the main channel of this reaction system based on the energy barriers calculated.In this study,the anharmonic effect is significant due to the calculated results that the rate constant of harmonic effect is close to the rate constant of anharmonic effect at 300 K,but the difference between them is nearly an order of magnitude when the temperature is close to 4800 K.Regarding the second reaction system,namely the cracking of CH3NHNHNO2,based on the fact that CH3NHNHNO2 has two kinds of structures,cis-CH3NHNHNO2 and trans-CH3NHNHNO2,this paper calculate the main channels of the cracking of these two structures,respectively.Compared with energy barriers obtained from some references,the energy barriers,which exist in each channel of these two reaction systems mentioned above,are similar with the references.On the other hand,after making analysis of these two cracking reaction systems,we learn that the anharmonic effect is more significant at high temperature or energy than low temperature or energy.Thereafter,it is worth considering the anharmonic effect on rate constant when the temperature or energy is high.