Acetone-h6 or -d6 + OH reaction products: evidence for heterogeneous formation of acetic acid in a simulation chamber.

Simulation chamber experiments have been carried out at room temperature to investigate the products of the acetone + OH and acetone-d6 + OH reactions using two photoreactors made of Teflon or Pyrex and coupled to GC-FTIR-FID analytical techniques. In the Pyrex chamber, the results demonstrated that the channel forming acetic acid is a minor oxidation route in the atmospheric acetone-h6 + OH reaction (yield <5%), whereas a higher yield of about 20% was obtained in the case of the acetone-d6 + OH reaction, in good agreement with previous studies. Existence of a heterogeneous way of formation of acetic acid has also been identified in the Teflon photoreactor.

Rate and equilibrium constant of the reaction of 1-methylvinoxy radicals with O2: CH3COCH2 + O2<--> CH3COCH2O2.

The reaction of 1-methylvinoxy radicals, CH3COCH2, with molecular oxygen has been investigated by experimental and theoretical methods as a function of temperature (291-520 K) and pressure (0.042-10 bar He). Experiments have been performed by laser photolysis coupled to a detection of 1-methylvinoxy radicals by laser-induced fluorescence LIF. The potential energy surface calculations were performed using ab inito molecular orbital theory at the G3MP2B3 and CBSQB3 level of theory based on the density function theory optimized geometries. Derived molecular properties of the characteristic points of the potential energy surface were used to describe the mechanism and kinetics of the reaction under investigation. At 295 K, no pressure dependence of the rate constant for the association reaction has been observed: k(1,298K) = (1.18 +/- 0.04) x 10(-12) cm3 s(-1). Biexponential decays have been observed in the temperature range 459-520 K and have been interpreted as an equilibrium reaction. The temperature-dependent equilibrium constants have been extracted from these decays and a standard reaction enthalpy of deltaH(r,298K) = -105.0 +/- 2.0 kJ mol(-1) and entropy of deltaS(r,298K) = -143.0 +/- 4.0 J mol(-1) K(-1) were derived, in excellent agreement with the theoretical results. Consistent heats of formation for the vinoxy and the 1-methylvinoxy radical as well as their O2 adducts are recommended based on our complementary experimental and theoretical study deltaH(f,298K) = 13.0 +/- 2.0, -32. 9+/- 2.0, -85.9 +/- 4.0, and -142.1 +/- 4.0 kJ mol(-1) for CH2CHO, CH3COCH2 radicals, and their adducts, respectively.

Variable pressure infrared diode laser spectroscopy: a new method for trace-gas monitoring.

A new method for measuring trace concentrations of atmospheric pollutants by infrared diode laser spectroscopy has been devised. This method relies on the increase of the signal as the pressure inside the cell increases, while the frequency of the diode is stabilized on the line, even if it is unresolved. Performances of this method were tested with N2O and with 1,3-butadiene. As an example of application, we measured the butadiene emitted by car exhausts. Sensitivity and rapidity of this method are equivalent to the usual scanning method in which the whole line is described, but this new method benefits from its simplicity and robustness.