Abstract:The use of a "well-stirred" or "homogeneous" reactor in kinetic studies of gas phase reactions has been examined to assess the sensitivity of the method to the criteria upon which its use is based. The effects of heterogeneous and homogeneous secondary reactions are considered and the validity of the assumption of homogeneity has been examined experimentally for conditions similar to those which have been used elsewhere. The atom sink presented by the excess reagent under pseudo first order conditions results … Show more
“…A general agreement was found among these values and the values compiled in ref and references therein for temperatures of 300 K. The three-body rate coefficient taken into account for reaction 8 has been considered at each moment of the simulation to depend on the relative concentration of the predominant species N 2 O, N 2 , and O 2 and their partial contribution as a third body. The individual values used here have been 1.59 × 10 -31 cm -6 s -1 , 6.83 × 10 -32 cm -6 s -1 , and 8.6 × 10 -32 cm -6 s -1 , respectively. These reactions are assumed to be irreversible, this assumption being justified by comparison of the reverse and forward rate constants. , Homogeneous reactions among two or three of the stable species involved in the discharge have not been considered in the model, since their reported rate coefficients are many orders of magnitude lower than those of reactions involving atoms.…”
Section: Chemical Kinetics Model and Discussionmentioning
The present work describes a systematic experimental investigation of a N 2 O hollow cathode discharge. The local electron mean energy and density have been determined with a double Langmuir probe. Fourier transform infrared spectroscopy and mass spectrometry have been employed for the measurement of the concentration of the stable species present in the discharge. N 2 O, N 2 , O 2 , and NO are always identified as the main constituents of the discharge plasma. In addition, NO 2 is found for the first time in a glow discharge of nitrous oxide. As a plausible explanation, a reaction of NO with oxygen atoms adsorbed on the cathode walls is proposed, although homogeneous reactions of vibrationally excited species cannot be discarded. A model based on a reduced set of kinetic equations including electron dissociation, gas-phase reactions, and gas-surface processes can give a global account of the measured data for all the experimental conditions used. The results are discussed and, when possible, compared to previous works on other types of N 2 O glow discharges.
“…A general agreement was found among these values and the values compiled in ref and references therein for temperatures of 300 K. The three-body rate coefficient taken into account for reaction 8 has been considered at each moment of the simulation to depend on the relative concentration of the predominant species N 2 O, N 2 , and O 2 and their partial contribution as a third body. The individual values used here have been 1.59 × 10 -31 cm -6 s -1 , 6.83 × 10 -32 cm -6 s -1 , and 8.6 × 10 -32 cm -6 s -1 , respectively. These reactions are assumed to be irreversible, this assumption being justified by comparison of the reverse and forward rate constants. , Homogeneous reactions among two or three of the stable species involved in the discharge have not been considered in the model, since their reported rate coefficients are many orders of magnitude lower than those of reactions involving atoms.…”
Section: Chemical Kinetics Model and Discussionmentioning
The present work describes a systematic experimental investigation of a N 2 O hollow cathode discharge. The local electron mean energy and density have been determined with a double Langmuir probe. Fourier transform infrared spectroscopy and mass spectrometry have been employed for the measurement of the concentration of the stable species present in the discharge. N 2 O, N 2 , O 2 , and NO are always identified as the main constituents of the discharge plasma. In addition, NO 2 is found for the first time in a glow discharge of nitrous oxide. As a plausible explanation, a reaction of NO with oxygen atoms adsorbed on the cathode walls is proposed, although homogeneous reactions of vibrationally excited species cannot be discarded. A model based on a reduced set of kinetic equations including electron dissociation, gas-phase reactions, and gas-surface processes can give a global account of the measured data for all the experimental conditions used. The results are discussed and, when possible, compared to previous works on other types of N 2 O glow discharges.
“…The rate coefficients for the OC-addition channel are shown by the dot-dashed line (with the WKB tunneling). The symbols show the experimental data: ⊗, ref ; □, ref ; ▵, ref , the MS-measured data; ○, ref , the ESR-measured data; ◇, ref ; **, ref ; +, ref ; ▿, ref ; × ×, ref .…”
Section: Resultsmentioning
confidence: 99%
“…The rate coefficients for the OC-addition channel are shown by the dot-dashed line (with the WKB tunneling). The symbols show the experimental data: ⊗, ref ; □, ref ; ▵, ref , the MS-measured data; ○, ref , the ESR-measured data; ◇, ref ; **, ref ; +, ref ; ▿, ref ; × ×, ref . 5 Kinetic isotope effect (KIE) for the O( 3 P) + CH 3 COCH 3 reaction in the temperature range 200−3000 K. The KIEs with the WKB tunneling and with the Eckart tunneling are shown by the solid line and the dot-dashed line, respectively. Δ, the experimental data in ref ; □, the theoretical data in ref .…”
Section: Resultsmentioning
confidence: 99%
“…As summarized in Table , all the experimental measurements of the rate coefficient were performed three decades ago, − and the rate coefficient data are scattered below 1000 K. It appears that the reaction of O( 3 P) with acetone is fairly slow. The room-temperature rate coefficient is about 10 -15 cm 3 molecule -1 s -1 , which is almost 2 orders of magnitude slower than that for the OH + CH 3 COCH 3 reaction.…”
Mechanisms and kinetics of the reaction of atomic oxygen with acetone have been investigated using ab initio quantum chemistry methods and transition state theory. The structures of the stationary points along the possible reaction pathways were obtained using the second-order Møller-Plesset theory and the coupled-cluster theory with single and double excitations with the triple-zeta quality basis sets. The energetics of the reaction pathways were calculated at the reduced second-order Gaussian-3 level and the extrapolated full coupled-cluster/complete basis set limit. The rate coefficients were calculated in the temperature range 200-3000 K, with the detailed consideration of the hindered internal rotation and the tunneling effect using Eckart and the semiclassical WKB approximations. It is shown that the predominant mechanism is the direct hydrogen abstraction producing hydroxyl and acetonyl radicals. Although the nucleophilic OC addition/elimination channel leading to CH3 and CO2 involves comparable barrier with the direct hydrogen abstraction channel, kinetically it cannot play any role in the overall reaction. It is predicted that the rate coefficients show positive temperature dependence in the range 200-3000 K and strong non-Arrhenius behavior. The tunneling effect plays a significant role. Moreover, the reaction has strong kinetic isotope effect. The calculated results are in good agreement with the available experimental data. The present rigorous theoretical work is helpful for the understanding of the characteristics of the reaction of atomic oxygen with acetone.
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