title: Formic acid catalyzed gas-phase reaction of H2O with SO3 and the reverse reaction: a theoretical study.
abstract: The formic acid catalyzed gas-phase reaction between H(2)O and SO(3) and its reverse reaction are respectively investigated by means of quantum chemical calculations at the CCSD(T)//B3LYP/cc-pv(T+d)z and CCSD(T)//MP2/aug-cc-pv(T+d)z levels of theory. Remarkably, the activation energy relative to the reactants for the reaction of H(2)O with SO(3) is lowered through formic acid catalysis from 15.97 kcal  mol(-1) to -15.12 and -14.83 kcal  mol(-1) for the formed H(2)O⋅⋅⋅SO(3) complex plus HCOOH and the formed H(2)O⋅⋅⋅HCOOH complex plus SO(3), respectively, at the CCSD(T)//MP2/aug-cc-pv(T+d)z level. For the reverse reaction, the energy barrier for decomposition of sulfuric acid is reduced to -3.07 kcal  mol(-1) from 35.82 kcal  mol(-1) with the aid of formic acid. The results show that formic acid plays a strong catalytic role in facilitating the formation and decomposition of sulfuric acid. The rate constant of the SO(3)+H(2)O reaction with formic acid is 10(5) times greater than that of the corresponding reaction with water dimer. The calculated rate constant for the HCOOH+H(2)SO(4) reaction is about 10(-13) cm(3)  molecule(-1)  s(-1) in the temperature range 200-280 K. The results of the present investigation show that formic acid plays a crucial role in the cycle between SO(3) and H(2)SO(4) in atmospheric chemistry.
authors.affiliation: College of Computer and Information Engineering, Guizhou University for Nationalities, Guiyang, 550025, China. wwwltcommon@sina.com
authors.forename: Bo
authors.initials: B
authors.lastname: Long
authors.forename: Zheng-wen
authors.initials: ZW
authors.lastname: Long
authors.forename: Yi-bo
authors.initials: YB
authors.lastname: Wang
authors.forename: Xing-feng
authors.initials: XF
authors.lastname: Tan
authors.forename: Yu-hua
authors.initials: YH
authors.lastname: Han
authors.forename: Chao-yun
authors.initials: CY
authors.lastname: Long
authors.forename: Shui-jie
authors.initials: SJ
authors.lastname: Qin
authors.forename: Wei-jun
authors.initials: WJ
authors.lastname: Zhang