PhD in Chemistry
thesis defended on 3rd October 2017
Laboratoire de PhysicoChimie des Processus de Combustion et de l'Atmosphère (PC2A)
Kinetic study of reactions with interest to atmospheric chemistry by simultaneous detection of OH and RO2 radicals coupled to laser photolysis
The hydroxyl radical OH and hydroperoxy radical HO2 radicals are key species in many oxidation processes in the atmosphere. The degradation of volatile organic compounds under tropospheric conditions is induced by reactions with hydroxyl radicals followed by the subsequent chemistry of the initial OH oxidation products with O2. This thesis was focused on the kinetic study of some of these atmospherically relevant reactions to better understand their oxidation mechanisms using an experimental system of laser photolysis coupled to Laser Induced Fluorescence (LIF, for OH radical) and continuous-wave Cavity Ring-Down Spectroscopy (cw-CRDS, for OH, HO2 and RO2 radicals) detection techniques.
After determining the infrared spectrum of OH, HO2 and CH3O2 radicals in the near infrared region and the absorption cross-sections of few selected lines, four systems were studied with the above mentioned techniques: CH3O2 + OH, C2H5O2 + OH, C3H7O2 + OH and C4H9O2 + OH. The rate constant and the HO2 yield of the four reactions were determined. In addition, the rate constants of few secondary reactions such as CH3O + HO2, CH3O + CH3O or OH + HO2 have been determined.
Thesis supervisor : Christa Fittschen et Coralie Schoemaecker
Referees : David Rowley et Geoffrey Tyndall
Examiners : Dwayne Heard, Yoshizumi Kajii, Votava Ondrej, Huet Thérèse et Jimenez Elena
Financing : Région Nord-Pas-de-Calais / Labex CaPPA
i) E. Assaf and C. Fittschen, “Cross Section of OH Radical Overtone Transition near 7028 cm-1 and Measurement of the Rate Constant of the Reaction of OH with HO2 Radicals,” J. Phys. Chem. A, vol. 120, no. 36, pp. 7051–7059, Sep. 2016.
(ii) E. Assaf, B. Song, A. Tomas, C. Schoemaecker, and C. Fittschen, “Rate Constant of the Reaction between CH3O2 Radicals and OH Radicals Revisited,” J. Phys. Chem. A, vol. 120, no. 45, pp. 8923–8932, Nov. 2016.
(iii) E. Assaf, L. Sheps, L. Whalley, D. Heard, A. Tomas, C. Schoemaeker, C. Fittschen, “The Reaction between CH3O2 and OH Radicals: Product Yields and Atmospheric Implications,” Environmental Science & Technology, vol. 51, no. 4, pp. 2170–2177, Feb. 2017.
(iv) D. Liu, F. Khaled, B. R. Giri, E. Assaf, C. Fittschen, and A. Farooq, “H-Abstraction by OH from Large Branched Alkanes: Overall Rate Measurements and Site-Specific Tertiary Rate Calculations,” J. Phys. Chem. A, vol. 121, no. 5, pp. 927–937, Feb. 2017.
(v) C. Fittschen, E. Assaf, and L. Vereecken, “Experimental and Theoretical Investigation of the Reaction NO + OH + O2→ HO2 + NO2,” J. Phys. Chem. A, vol. 121, no. 24, pp. 4652–4657, Jun. 2017.
(vi) E. Assaf, S. Tanaka, Y. Kajii, C. Schoemaecker, and C. Fittschen, “Rate Constants of the Reaction of C2–C4 Peroxy Radicals with OH Radicals,” Chemical Physics Letters, vol. 684, pp. 245–249, Sep. 2017.
(vii) E. Assaf, O. Asvany, O. Votava, S. Batut, C. Schoemaecker, and C. Fittschen, “Measurement of line strengths in the Ã 2A’ ← 2A” transition of HO2 and DO2,” Journal of Quantitative Spectroscopy and Radiative Transfer, vol. 201, pp. 161–170, Nov. 2017.
Participation at more than 10 national and international conferences
Best poster award at the french conference "Colloque du Groupe Français de Cinétique et Photochimie 2017"
20-21 June 2017 - Douai