Kinetics and Mechanism of the Tropospheric Reaction of 3-Hydroxy-3-methyl-2-butanone with Cl Atoms

An experimental study of the gas-phase reaction between Cl atoms and trans-2-pentenal: Kinetics, products and SOA formation

The gas-phase reaction of trans-2-pentenal (T2P) with Cl atoms was studied at atmospheric pressure and room temperature. A rate coefficient of (2.56 ± 0.83) × 10^-10 cm³ molecule^-1 s^-1 was obtained using the relative rate method and isoprene, cyclohexane and ethanol as reference compounds. The kinetic study was carried out using a 300-L Teflon bag simulation chamber (IMT Lille Douai-France) and a 16-L Pyrex cell (UCLM-Ciudad Real-Spain), both coupled to the Fourier transform infrared (FTIR) technique. Gas-phase products and secondary organic aerosol (SOA) formation were studied at UCLM using a 16-L Pyrex cell and a 264-L quartz simulation chamber coupled to the FTIR and gas-chromatography-mass spectrometry (GC-MS) techniques. HCl, CO, and propanal were identified as products formed from the studied reaction and quantified by FTIR, the molar yield of the latter being (5.2 ± 0.2)%. Formic acid was identified as a secondary product and was quantified by FTIR with a yield of (6.2 ± 0.4)%. In addition, 2-chlorobutanal and 2-pentenoic acid were identified, but not quantified, by GC-MS as products. The SOA formation was investigated using a fast mobility particle sizer spectrometer. The observed SOA yields reached maximum values of around 7% at high particle mass concentrations. This work provides the first study of the formation of gaseous and particulate products for the reaction of Cl with T2P. A reaction mechanism is suggested to explain the formation of the observed gaseous products. The results are discussed in terms of structure-reactivity relationship, and the atmospheric implications derived from this study are commented as well.

Photo-Oxidation Reaction Kinetics and Mechanistics of 4-Hydroxy-2-butanone with Cl Atoms and OH Radicals in the Gas Phase

The temperature-dependent rate coefficients for the gas-phase reaction of 4-hydroxy-2-butanone (4H2BN) with Cl atoms and OH radicals were explored experimentally using relative rate technique and computational methods. The concentrations of the reactants as well as products were followed using gas chromatography (GC) with the flame ionization detector, GC/mass spectrometry, and GC/infrared spectroscopy as analytical techniques. Formaldehyde was obtained as the major product during the title reaction. The kinetics of 4H2BN with Cl atoms and OH radicals were measured over the temperature range of 298-363 K at 760 Torr in the N₂ atmosphere using C₃H₈, C₂H₄, isopropanol, and n-propanol as reference compounds. The temperature-dependent rate coefficients for the reaction of 4H2BN with Cl atoms and OH radicals were obtained as k_Expt( T) = [(1.52 ± 0.86) × 10^-26] T⁵ exp[(2474 ± 450)/ T] cm³ molecule^-1 s^-1 and k_expt( T) = [(2.09 ± 0.24) × 10^-12] exp[-(409 ± 15)/ T] cm³ molecule^-1 s^-1, respectively. Theoretical calculations were carried out at the M062X/6-31G(d,p) and M06-2X/6-31+G(d,p) level of theories, and the rate coefficients for H abstraction reactions were evaluated using the canonical variational transition state theory with the inclusion of small-curvature tunneling correction over the temperature range of 200-400 K. The rate coefficients obtained over the studied temperature range were used to fit the data, and the Arrhenius expression was obtained to be k_Cl(Theory) (200-400 K) = (6.10 × 10^-25) T^4.42 exp(2397/ T) cm³ molecule^-1 s^-1, k_OH(Theory) (200-400 K) = (1.13 × 10^-19) T^2.27 exp(1505/ T) cm³ molecule^-1 s^-1, respectively, for the reactions of Cl atoms and OH radicals with 4H2BN. The possible reaction mechanism proposed based on the obtained products for the title reaction, thermochemistry, branching ratios, and atmospheric implications and cumulative lifetime of 4H2BN were also explored in this study.

Atmospheric Reaction of Cl with 4-Hydroxy-2-pentanone (4H2P): A Theoretical Study

The kinetics and the mechanism of the reaction of 4-hydroxy-2-pentanone (4H2P) with Cl atom were investigated using quantum theoretical calculations. Density functional theory, CBS-QB3, and G3B3 methods are used to explore the reaction pathways. Rice-Ramsperger-Kassel-Marcus theory is employed to obtain rate constants of the reaction at atmospheric pressure and the temperature range 278-400 K. This study provides the first theoretical and kinetic determination of Cl rate constant for reactions with 4H2P over a large temperature range. The obtained rate constant 1.47 × 10^-10 cm³ molecule^-1 s^-1 at 298 K is in reasonable agreement with those obtained for C4-C5 hydroxyketones both theoretically and experimentally. The results regarding the structure-reactivity relationship and the atmospheric implications are discussed.

An experimental and theoretical study of the kinetics of the reaction between 3-hydroxy-3-methyl-2-butanone and OH radicals

Absolute experimental and theoretical rate constants are determined for the first time for the reaction of 3-hydroxy-3-methyl-2-butanone with OH as a function of temperature. The atmospheric implications are discussed.