Photolysis of CH3CHO at 248 nm: Evidence of triple fragmentation from primary quantum yield of CH3 and HCO radicals and H atoms

Radical quantum yields have been measured following the 248 nm photolysis of acetaldehyde, CH3CHO. HCO radical and H atom yields have been quantified by time resolved continuous wave Cavity Ring Down Spectroscopy in the near infrared following their conversion to HO2 radicals by reaction with O2. The CH3 radical yield has been determined using the same technique following their conversion into CH3O2. Absolute yields have been deduced for HCO radicals and H atoms through fitting of time resolved HO2 profiles, obtained under various O2 concentrations, to a complex model, while the CH3 yield has been determined relative to the CH3 yield from 248 nm photolysis of CH3I. Time resolved HO2 profiles under very low O 2 concentrations suggest that another unknown HO2 forming reaction path exists in this reaction system besides the conversion of HCO radicals and H atoms by reaction with O2. HO2 profiles can be well reproduced under a large range of experimental conditions with the following quantum yields: CH3CHO+hν248nm → CH 3CHO*, CH3CHO* → CH3+HCO φ1a = 0.125±0.03, CH3CHO* → CH 3+H+CO φ1e = 0.205±0.04, CH 3CHO* o2→ CH3CO+HO2 φ1f = 0.07±0.01. The CH3O2 quantum yield has been determined in separate experiments as φCH3 = 0.33 ± 0.03 and is in excellent agreement with the CH3 yields derived from the HO2 measurements considering that the triple fragmentation (R1e) is an important reaction path in the 248 nm photolysis of CH3CHO. From arithmetic considerations taking into account the HO2 and CH3 measurements we deduce a remaining quantum yield for the molecular pathway: CH3CHO* → CH 4+CO φ1b = 0.6. All experiments can be consistently explained with absence of the formerly considered pathway: CH 3CHO* → CH3CO+H φ1c = 0. © 2014 AIP Publishing LLC.Fil: Pranay Morajkar. University Of Lille.; FranciaFil: Bossolasco, Adriana Gabriela. University Of Lille.; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Schoemaecker, Coralie. University Of Lille.; FranciaFil: Fittschen, Christa. University Of Lille.; Franci

A modelling study of the impact of photolysis on indoor air quality

The importance of photolysis as an initiator of air chemistry outdoors is widely recognized, but its role in chemical processing indoors is often ignored. This paper uses recent experimental data to modify a detailed chemical model, using it to investigate the impacts of glass type, artificial indoor lighting, cloudiness, time of year and latitude on indoor photolysis rates and hence indoor air chemistry. Switching from an LED to an uncovered fluorescent tube light increased predicted indoor hydroxyl radical concentrations by ~13%. However, moving from glass that transmitted outdoor light at wavelengths above 380 nm to one that transmitted sunlight above 315 nm led to an increase in predicted hydroxyl radicals of more than 400%. For our studied species, including ozone, nitrogen oxides, nitrous acid, formaldehyde, and hydroxyl radicals, the latter were most sensitive to changes in indoor photolysis rates. Concentrations of nitrogen dioxide and formaldehyde were largely invariant, with exchange with outdoors and internal deposition controlling their indoor concentrations. Modern lights such as LEDs, together with low transmission glasses, will likely reduce the effects of photolysis indoors and the production of potentially harmful species. Research is needed on the health effects of different indoor air mixtures to confirm this conclusion

The past, present and future of indoor air chemistry

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Diagnostics laser dans une flamme de diffusion (imagerie quantitative de nanoparticules de suies et d'espèces majoritaires et minoritaires)

Les principales sources d'énergies actuelles sont basées sur la combustion d'hydrocarbures qui peut être le siège de la formation de particules de suies. L'émission de suies entraîne une baisse du rendement énergétique des installations mais surtout ces particules carbonées ont un effet néfaste sur la santé. En effet, les suies de petites tailles (quelques nanomètres) sont assimilées par l'organisme. Leur présence est associée à celle des Hydrocarbures Aromatiques Polycycliques (HAP) qui sont reconnus comme cancérigènes. Il apparaît primordial de développer de nouvelles techniques quantitatives de détection dans des systèmes en combustion afin de doser les nanoparticules de suies ainsi que la phase gaz. Appliqués à des flammes, les diagnostics laser offrent des méthodes de dosage non intrusives et produisent une mesure instantanée avec une bonne sensibilité et sélectivité. Ce travail de thèse a permis d'étendre le potentiel des diagnostics laser utilisés au laboratoire à l'étude de flammes produisant des suies avec la mise en œuvre notamment de techniques d'imagerie laser. Ces études ont été réalisées dans une flamme de diffusion laminaire stabilisée sur un brûleur Wolfhard-Parker contenant des suies en teneurs variables. Les espèces majoritaires ont été mesurées par diffusion Raman et la température par diffusion Raman/Rayleigh. Des stratégies de détections originales par Fluorescence Induite par Laser des radicaux CH et OH ont été mises en œuvre en présence de suies. Un effort important a été consacré au développement d'une technique novatrice appelée Incandescence Induite par Laser qui permet la détection de nanoparticules présentant des fractions volumiques de quelques ppb. Cette technique a été couplée à la Cavity-Ring-Down-Spectroscopy afin d'obtenir des cartographies quantitatives de nanoparticules [...]LILLE1-BU (590092102) / SudocSudocFranceF

Yield of HO₂ Radicals in the OH-Initiated Oxidation of SO₂

Abstract The HO2 radical yield in the OH initiated oxidation of SO2 has been determined by direct observation of HO2 concentration time profiles following the 248 nm photolysis of H2O2/SO2/O2 mixtures. Initial OH radical concentrations have been deduced from a fit of the absolute HO2 concentration time profiles after 248 nm photolysis of H2O2 in the absence of SO2, an increase in the HO2 concentration upon addition of SO2 to this reaction mixture is observed and can be explained by a decrease of HO x -radical losses due to a faster decay of OH radicals in the presence of SO2. Simulations of theses profiles using recommended rate constants in a simple model are in agreement with an HO2-yield of 1.0 ± 0.1 from the OH initiated oxidation of SO2.</jats:p

Absorption spectrum and absorption cross sections of the 2ν 1 band of HO 2 between 20 and 760 Torr air in the range 6636 and 6639 cm −1

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The reaction of fluorine atoms with methanol: yield of CH 3 O/CH 2 OH and rate constant of the reactions CH 3 O + CH 3 O and CH 3 O + HO 2

Xenondifluoride, XeF2, has been photolysed in the presence of methanol, CH3OH. Two reaction pathways are possible: F + CH3OH → CH2OH + HF and F + CH3OH → CH3O + HF. Both products, CH2OH and CH3O, will be converted to HO2 in the presence of O2. The rate constants for the reaction of both radicals with O2 differ by more than 3 orders of magnitude, which allows an unequivocal distinction between the two reactions when measuring HO2 concentrations in the presence of different O2 concentrations. The following yields have then been determined from time-resolved HO2 profiles: ϕCH2OH = (0.497 ± 0.013) and ϕCH3O = (0.503 ± 0.013). Experiments under low O2 concentrations lead to reaction mixtures containing nearly equal amounts of HO2 (converted from the first reaction) and CH3O (from the second reaction). The subsequent HO2 decays are very sensitive to the rate constants of the reaction between these two radicals and the following rate constants have been obtained: k(CH3O + CH3O) = (7.0 ± 1.4) × 10−11 cm3 s−1 and k(CH3O + HO2) = (1.1 ± 0.2) × 10−10 cm3 s−1. The latter reaction has also been theoretically investigated on the CCSD(T)//M06-2X/aug-cc-pVTZ level of theory and CH3OH + O2 have been identified as the main products. Using μVTST, a virtually pressure independent rate constant of k(CH3O + HO2) = 4.7 × 10−11 cm3 s−1 has been obtained, in good agreement with the experiment