A catalytic mechanism for the SO3+CH3OH reaction with the acidic,neutral and basic trace gases
The reaction between sulfur trioxide(SO3)and methanol(CH3OH)can form the methyl hydrogen sulfate(MHS),which was recognized as a potential nucleating species and can effectively promote the new particles formation in atmospheric.However,the SO3+CH3OH reaction with acidic(H2SO4),neu-tral(H2O)and basic(NH3)trace gases have not been reported.Herein,the SO3+CH3OH reaction assisted by acidic(H2SO4),neutral(H2O)and basic(NH3)trace gases have been studied theoretically by using quantum chemical method of CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/6-311 +G(2df,2pd)and the Master Equation(ME/RRKM)calculation.The calculation results showed that the addition of H2O,H2SO4 and NH3 has not only increased the stabilization energies of the pre-reactive complexes by0.5～7.3 kcal/mol,but also decreased the energy barriers by at least 14.9 kcal/mol.Moreover,the SO3+CH3OH reaction with NH3 is a barrierless process.Effective rate constant calculations suggest that H2O is 3～8 orders of magnitude more effi-cient catalyst than H2SO4 and NH3 within 0～15 km due to its relatively higher concentration.Meanwhile,the effective rate constants of H2O catalyzed reaction were 8 orders of magnitude larger than the rate constant of the SO3+CH3OH reaction.This indicates that the contribution of H2O is obvious in the SO3 + CH3OH reaction.This study will provide new insight for the effects of acidic,neutral and basic trace gases on the SO3+CH3OH reaction in the atmospheric environment.
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