4400-01-5Relevant academic research and scientific papers
Formation of HO2 from OH and C2H2 in the presence of O2
Bohn, Birger,Zetzsch, Cornelius
, p. 1203 - 1210 (2007/10/03)
Pulsed production of OH in a gas-phase system containing acetylene, O2 and NO resulted in biexponential OH-decay curves, indicating formation of HO2 in secondary reactions.Production and detection of OH were performed by 248 nm photolysis of H2O2 and cw-laser long-path absorption at 308 nm, respectively.Measurements were made at room temperature in O2 or N2-O2 mixtures containing 5percent O2 at total pressures between 10 and 100 kPa.Analysis of the decay curves resulted in effective rate constants for the removal of OH and the formation of HO2 by acetylene in the presence of O2 in the range (1.4-3.5) x 10-13 cm3 s-1, dependent on total pressure and O2 concentration.HO2 is thought to be formed from HCO and O2, with HCO originating in a reaction of an intermediate acetylene-OH adduct with O2.HO2 yields were found to vary between 1.13 and 1.01 and tending to higher values at lower total pressures.These yields are higher than the expected value of 1, which can be explained by a dissociation of a small fraction of vibrationally excited glyoxal formed, together with OH in a second channel of the acetylene-OH adduct + O2 reaction.In order to check whether the increased HO2 yields are real, CO was used instead of acetylene.In this case, an HO2 yield of 0.99 was found, in good agreement with expectations, and a rate constant of (1.66 +/- 0.25) x 10-13 cm3 s-1 for the OH + CO reaction in 20 kPa O2 was determined.In addition, a rate constant for the HO2 + NO reaction of (9.5 +/- 1.5) x 10-12 cm3 s-1, rate constants for the OH + NO reaction in the range (1.3-7.4) x 10-12 cm3 s-1, depending on total pressure, and upper limits for the rate constants of possible reactions HO2 + C2H2 (k =-15 cm3 s-1) and HO2 + CO (k =-15 cm3 s-1) were derived.Error limits include statistical (2?) and possible systematic errors.
Branching Ratios in O(3P) Reactions of Terminal Olefins Studied by Kinetic Microwave Absorption Spectroscopy
Koda, Seiichiro,Endo, Yasuki,Tsuchiya, Soji,Hirota, Eizi
, p. 1241 - 1244 (2007/10/02)
O(3P) atom reactions with ethylene, propylene, and 1-butene were studied by use of kinetic microwave absorption spectroscopy where the atomic oxygen was supplied via ArF excimer laser photolysis of SO2.Time evolutions of vinoxy, HCO, and H2CO were pursued.The fraction of vinoxy production in the propylene and 1-butene reactions at 30 mTorr was found to be 0.29 +/- 0.15 and 0.37 +/- 0.15, respectively.The fractions seemed to increase with decrease in pressure, by comparing the present results with those of several previous researchers.Therefore, at least some part of the vinoxy production fraction is pressure dependent.The reaction scheme explaining the pressure-dependent part is suggested as follows.Initially, a triplet biradical is produced through O(3P) attack to the terminal carbon atom of the C=C double bond, which is then converted to a singlet biradical.Subsequently, a hydrogen atom migrates and then the C-C bond adjacent to the original C=C double bond dissociates to yield the vinoxy and corresponding alkyl radicals.Thus, some part of the vinoxy radical is produced via a quite different mechanism from the case of ethylene reaction, where it is produced via a direct substitution channel on a triplet surface.
Microwave kinetic spectroscopy of reaction intermediates: O + ethylene reaction at low pressure
Endo, Yasuki,Tsuchiya, Soji,Yamada, Chikashi,Hirota, Eizi,Koda, Seiichiro
, p. 4446 - 4452 (2007/10/02)
A microwave spectroscopic method has been developed to study elementary reactions in real time through in situ observation of rotational spectra of reaction intermediates such as free radicals with lifetime as short as 1 ms.This method was applied to the O(3P) + ethylene reaction in order to assess the roles of (a) vinoxy + H and (b) CH3 + CHO channels in the initial process.The reaction was initiated by irradiating an N2O/C2H4 mixture containing a trace amount of mercury with the 253.7 nm mercury resonance line, and the time evolution of vinoxy, HCO, and H2CO was followed by measuring their microwave absorption intensities as functions of time.The branching ratio was thus determined to be 0.4 +/- 0.1 and 0.5 +/- 0.1 for (a) and (b), respectively, at the sample pressure of 30 mTorr.The present result agrees with those obtained by Hunziker et al. using much higher pressures of samples, but is not compatible with the observation of Buss et al. that (a) is dominant in collision-free conditions.
Kinetics of the Reactions between CH2(3B1)-Radicals and Saturated Hydrocarbons in the Temperature Range 296 K
Boehland, T.,Dobe, S.,Temps, F.,Wagner, H. Gg.
, p. 1110 - 1116 (2007/10/02)
The reaction between CH2-radicals in their ground electronic state (3B1) and n-hexane CH2() + n-C6H14 --> CH3 + C6H13 was studied in a discharge flow system with LMR detection of CH2.In the temperature regime 413 K 4 = 1E(13.22 +/- 0.20)*exp(-3380 +/- 240/T) cm3/mol s.The reaction proceeds both via direct H-atom abstraction by CH2() and via thermal excitation of CH2() to the low-lying singlet state (1A1) followed by fast consecutive reactions of CH2().The contributions due to thermal excitation and singlet reaction were evaluated for the present work as well as for a recent study of the reactions of CH2() with a series of other hydrocarbons.Corrected rate constants kT for the direct reactions of CH2() with the reactants HR = CH4 (1), C2H6 (2), C3H8 (3), n-C6H14 (4), i-C4H10 (5), and CH3CHO (6) in the temperature range 296 K 1T = 4.3E12*exp(-42 kJ mol-1/RT) cm3/mol s, k2T = 6.5E12*exp(-33.1 kJ mol-1/RT) cm3/mol s, k3T = 4.9E12*exp(-27.7 kJ mol-1/RT) cm3/mol s, k4T = 7.8E12*exp(-25.6kJ mol-1/RT) cm3/mol s, k5T = 2.5E12*exp(-22.5 kJ mol-1/RT) cm3/mol s, k6T = 1.7E12*exp(-14.7 kJ mol-1/RT) cm3/mol s.The activation energies for the reactions studied are described by an Evans Polanyi type relation.Arrhenius expressions are proposed for the rate constants of H-atom abstraction by CH2(3B1) from primary, secondary, tertiary, and aldehydic C-H bonds.The results are compared to the isoelectronic reactions of O(3P). - Keywords: Chemical Kinetics / Elementary Reactions / Radicals / Spectroscopy, Laser Magnetic Resonance
