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.

High pressure experiments on the OH + NO2 reaction are presented for 3 different temperatures. At 300 K, experiments in He (p = 2-500 bar) as well as in Ar (p = 2-4 bar) were performed. The rate constants obtained in Ar agree well with values which have been reported earlier by our group (Forster, R.; Frost, M.; Fulle, D.; Hamann, H. F.; Hippler, H.; Schlepegrell, A.; Troe, J. J. Chem. Phys. 1995, 103, 2949. Fulle, D.; Hamann, H. F.; Hippler, H.; Troe, J. J. Chem. Phys. 1998, 108, 5391). In contrast, the rate coefficients determined in He were found to be 15-25% lower than the values given in our earlier publications. Additionally, results for He as bath gas at elevated temperatures (T = 400 K, p = 3-150 bar; T = 600 K, p = 3-150 bar) are reported. The results obtained at elevated pressures are found to be in good agreement with existing literature data. The observed falloff behavior is analyzed in terms of the Troe formalism taking into account two reaction channels: one yielding HNO3 and one yielding HOONO. It is found that the extracted parameters are in agreement with rate constants for vibrational relaxation and isotopic scrambling as well as with experimentally determined branching ratios. Based on our analysis we determine falloff parameters to calculate the rate constant for atmospheric conditions.

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