Study On The Calculation Of The Anharmonic Effect Of Several Nitrogen Compounds In Combustion Process

Ocean transportation is most widely used in world trading system,and diesel engine brings massive pollution.As one of the main air pollutants from marine engine emission,NOx attracts much attention in its generation and elimination mechanism.Several nitrogen compounds(CN,NCO,NH2 and NH3)have been regarded as the important intermediates in nitrogen fuel combustion process,which play an important role in NOx formation mechanism.This study is supposed to make a contribution in the studying of NOx formation mechanism,and a more profound understanding in combustion reaction.Gaussian 09 was applied to optimize the structures at B3LYP/6-311++G(d,p)level.Using QCISD(T)/CCSD(T)method,single point energies were calculated at the same level.Besides,the barrier heights were acquired after zero point energy correction.In order to investigate the anharmonic effect,the rate constants have been calculated according to RRKM(Rice-Ramsperger-Kassel-Marcus)theory and YL(Yao-Lin)method.For bimolecular reactions,the anharmonic effect has been discussed in canonical cases.The results calculated indicate that an extremely obvious anharmonic effect exits in biomolecular reactions.Where the rate constants increase along the increasing temperature,and the difference between harmonic and anharmonic rate constants is extremely obvious in high temperature,which reflects a significant anharmonic effect for bimolecular reactions.While in unimolecular case,the calculated results give different characteristics.In canonical systems,the results calculated indicate that the anharmonic effect is obvious under high temperature.While in 2000 K,the anharmonic effect is not so significant.The same results can also be found in micro-canonical systems where the anharmonic effect is obvious under the total energy corresponds to the temperature of 2000 K.What can be concluded is that the reaction temperature and total energy play an important role in anharmonic effect,which need to be concerned especially under high temperature and total energy.