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Louis F.,CNRS Atmospheric and Combustion Chemistry Laboratory
International Journal of Chemical Kinetics | Year: 2015

The rate constants of the H-abstraction reactions from cyclopropane by H, O (3P), Cl (2P3/2), and OH radicals have been calculated over the temperature range of 250-2500 K using two different levels of theory. Calculations of optimized geometrical parameters and vibrational frequencies are performed using the MP2 method combined with the cc-pVTZ basis set and the 6-311++G(d,p) basis set. Single-point energy calculations have been carried out with the highly correlated ab initio coupled cluster method in the space of single, double, and triple (perturbatively) electron excitations CCSD(T) using either the cc-pVTZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets or the 6-311++G(3df,3pd) basis set. The CCSD(T) calculated potential energies have been extrapolated to the complete basis limit (CBS) limit. The Full Configuration Interaction (FCI) energies have been also estimated using the continued-fraction approximation as proposed by Goodson (J. Chem. Phys., 2002, 116, 6948-6956). Canonical transition-state theory combined with an Eckart tunneling correction has been used to predict the rate constants as a function of temperature using two kinetic models (direct abstraction or complex mechanism) at two levels of theory (CCSD(T)-cf/CBS//MP2/cc-pVTZ and CCSD(T)-cf/6-311++G(3df,3pd)//MP2/6-311++G(d,p)). The calculated kinetic parameters are in reasonable agreement with their literature counterparts for all reactions. In the light of these trends, the use of the Pople-style basis sets for studying the reactivity of other systems such as larger cycloalkanes or halogenated cycloalkanes is recommended because the 6-311++G(3df,3pd) basis set is less time consuming than the aug-cc-pVQZ basis set. Based on our calculations performed at the CCSD(T)-cf/CBS//MP2/cc-pVTZ level of theory, the standard enthalpy of formation at 298 K for the cyclopropyl radical has been reassessed and its value is (290.5 ± 1.6) kJ mol-1. © 2015 Wiley Periodicals, Inc. Source

Thiebaud J.,CNRS Atmospheric and Combustion Chemistry Laboratory | Thiebaud J.,SRI International | Thevenet F.,Ecole Des Mines de Douai | Fittschen C.,CNRS Atmospheric and Combustion Chemistry Laboratory
Journal of Physical Chemistry C | Year: 2010

The formation of OH radicals and their diffusion into the gas phase after UV-excitation of TiO2 in the presence of H2O has been studied using the very sensitive and selective detection method of laserinduced fluorescence (LIF). The time-resolved evolution of the OH radical concentration has been observed at different pressures and at varying distances between the photocatalytic surface and the detection volume. H2O2 has been indirectly detected by LIF. The influence of O2, hydrocarbons, and excitation laser wavelength on the evolution of both species profiles has been studied in this work. The quantum yield for the formation of OH and H2O2 has been estimated by comparison with signals obtained after photolysis of H2O2 in the gas phase. © 2010 American Chemical Society. Source

Faccinetto A.,CNRS Atmospheric and Combustion Chemistry Laboratory | Faccinetto A.,CNRS Atomic and Molecular Physics Laboratory | Desgroux P.,CNRS Atmospheric and Combustion Chemistry Laboratory | Ziskind M.,CNRS Atomic and Molecular Physics Laboratory | And 2 more authors.
Combustion and Flame | Year: 2011

Species adsorbed at the surfaces of soot particles sampled at different locations in a low-pressure methane flame have been analyzed. The analysis method is laser desorption/laser ionization/time-of-flight mass spectrometry (LD/LI/TOF-MS) applied to soot particles deposited on a filter after probe extraction in the flame. In order to fully characterize the experimental apparatus, a strategy of systematic investigations has been adopted, beginning with the study of less complex systems constituted by model soot (standard polycyclic aromatic hydrocarbons, PAHs, adsorbed on black carbon), and then natural soot sampled from a literature reference ethylene flame. This characterization allowed a good understanding of the analytical response of PAHs to the desorption and ionization processes and the definition of the optimal experimental conditions. The soot PAH content was then investigated on a low-pressure methane/oxygen/nitrogen premixed flat flame (φ= 2.32) as a function of the sampling height above the burner (HAB). The obtained mass spectra are reproducible, fragment-free, well resolved in the analyzed m/. z range and they are characterized by an excellent signal-to-noise ratio. They all feature regular peak sequences, where each signal peak has been assigned to the most stable high-temperature-formed PAHs. The structure of the mass spectra depends on the sampling HAB into the flame, i.e., on the reaction time. An original contribution to the data interpretation comes from the development of a new sampling method that makes it possible to infer hypotheses about the PAH partition between the gas phase and the soot particles. This method highlights the presence of high-mass PAHs in the soot nucleation zone, and it suggests the importance of heterogeneous reactions occurring between flame PAHs and soot particles. © 2010 The Combustion Institute. Source

Carteret M.,CNRS Atmospheric and Combustion Chemistry Laboratory | Pauwels J.-F.,CNRS Atmospheric and Combustion Chemistry Laboratory | Hanoune B.,CNRS Atmospheric and Combustion Chemistry Laboratory
Indoor Air | Year: 2012

Laboratory measurements of the gaseous emission factors (EF) from two recent kerosene space heaters (wick and injector) with five different fuels have been conducted in an 8-m3 environmental chamber. The two heaters tested were found to emit mainly CO2, CO, NO, NO2, and some volatile organic compounds (VOCs). NO2 is continuously emitted during use, with an EF of 100-450μg per g of consumed fuel. CO is normally emitted mainly during the first minutes of use (up to 3mg/g). Formaldehyde and benzene EFs were quantified at 15 and 16μg/g, respectively, for the wick heater. Some other VOCs, such as 1,3-butadiene, were detected with lower EFs. We demonstrated the unsuitability of a 'biofuel' containing fatty acid methyl esters for use with the wick heater, and that the accumulation of soot on the same heater, whatever the fuel, leads to a dramatic increase in the CO EF, up to 16mg/g, which could be responsible for chronic and acute CO intoxications. © 2011 John Wiley & Sons A/S. Source

Gasnot L.,CNRS Atmospheric and Combustion Chemistry Laboratory | Dao D.Q.,CNRS Atmospheric and Combustion Chemistry Laboratory | Pauwels J.F.,CNRS Atmospheric and Combustion Chemistry Laboratory
Energy and Fuels | Year: 2012

An experimental and kinetic study of the influence of additives on the selective noncatalytic reduction (SNCR) process is presented. Experiments were performed on a lab-scale reactor suitable to investigate the influence of important operating parameters (flue gas temperature, residence time, amount of reducing agent, initial NO x concentration, etc.) on the SNCR efficiency. Several chemical compounds such as CH 4, C 2H 6, C 2H 4, C 2H 2, CH 3OH, C 2H 5OH, and CO, which are usually used in the literature as additives for the SNCR process, have been evaluated. The experimental results prove that the use of such additives allows the NO reduction process to be more efficient at lower temperatures. Furthermore, they induce a downward shift up to more than 100 K of the optimal temperature window for the reduction process. Four detailed kinetic mechanisms available in the literature have been tested to model our experimental results. The one that presents the better agreement between experiment and modeling has been optimized to explain the kinetic influence of the additives on the classical SNCR process. The main reaction pathways involved have been pointed out, illustrating the important role of OH radical. © 2012 American Chemical Society. Source

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