title: Rate coefficients and equilibrium constant for the CH2CHO + O2 reaction system.
abstract: The kinetics of the CH2CHO + O2 reaction was experimentally studied in two quasi-static reactors and a discharge flow-reactor at temperatures ranging from 298 to 660 K and pressures between 1 mbar and 46 bar with helium as the bath gas. The CH2CHO radicals were produced by the laser-flash photolysis of ethyl vinyl ether at 193 nm and by the reaction F + CH3CHO, respectively. Laser-induced fluorescence excited at 337 or 347.4 nm was used to monitor the CH2CHO concentration. The reaction proceeded via reversible complex formation with subsequent isomerization and fast decomposition: CH2CHO + O2 <= => O2CH2CHO --> HO2CH2CO --> products. The rate coefficients for the first and second steps were determined (k1, k-1, k2) and analyzed by a master equation with specific rate coefficients from the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Molecular and transition-state parameters were obtained from quantum chemical calculations. A third-law analysis led to the following thermodynamic parameters for the first step: Delta(R)S degrees 300K(1) = -144 J K(-1) mol(-1) (1 bar) and Delta(R)H degrees 300K(1) = (-101 +/- 4) kJ mol(-1). From the falloff analysis, the following temperature dependencies for the low- and high-pressure limiting rate coefficients were obtained: k1(0) = 5.14 x 10(-14) exp(210 K/T) cm(-3) s(-1); k1(infinity) = 1.7 x 10(-12) exp(-520 K/T) cm(-3) s(-1); and k2(infinity) = 1.3 x 10(12) exp[-(82 +/- 4) kJ mol(-1)/RT] s(-1). Readily applicable analytical representations for the pressure and temperature dependence of k1 were derived to be used in kinetic modeling.
authors.affiliation: Physicochimie des Processus de Combustion et de l'Atmosphere UMR CNRS 8522 and Centré d'Etudes et Recherches Lasers et Applications, Université des Sciences et Technologies de Lille 1, 59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Delbos
authors.forename: Christa
authors.initials: C
authors.lastname: Fittschen
authors.forename: Horst
authors.initials: H
authors.lastname: Hippler
authors.forename: Nikolina
authors.initials: N
authors.lastname: Krasteva
authors.forename: Matthias
authors.initials: M
authors.lastname: Olzmann
authors.forename: Bela
authors.initials: B
authors.lastname: Viskolcz