Atmospheric chemistry of hexa- and penta-fluorobenzene: UV photolysis and kinetics and mechanisms of the reactions of Cl atoms and OH radicals. Issue 45 (12th November 2018)

• Record Type: Journal Article
• Authors: Sulbaek Andersen, Mads P.; Lengkong, Jonathan W.; Wallberg, Jens; Hasager, Freja; Vo, Karen; Andersen, Simone Thirstrup; Kjaergaard, Henrik G.; Wallington, Timothy J.; Nielsen, Ole John
• Is Part Of: Physical chemistry chemical physics. Volume 20:Issue 45(2018)
• Page Start: 28796
• Page End: 28809
• Publication Date: 2018-11-12
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c8cp05540h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Chamber studies show that the atmospheric fates of aromatic Cl- and OH adducts are very different. Abstract : Photochemical reactors were used to study the kinetics and mechanisms of reactions of Cl atoms and OH radicals with hexa- and penta-fluorobenzene (C6 F6, C6 F5 H) in 700 Torr total pressure of N2, air, or O2 diluent at 296 ± 2 K. C6 F6 and C6 F5 H undergo ring-opening following 254 nm UV irradiation, but with small quantum yields ( φ < 0.03). Reaction of Cl atoms with C6 F6 proceeds via adduct formation, while the reaction of Cl atoms with C6 F5 H proceeds via hydrogen abstraction and adduct formation. C6 F6 –Cl and C6 F5 H–Cl adducts decompose rapidly ( k ∼ 10 5 –10 6 s −1 ) reforming the reactants, and react with Cl atoms to form products. The fraction of adduct reacting with Cl atoms increases with steady state Cl atom concentration, resulting in an increasing apparent effective Cl atom rate constant. The rate constant for the H-abstraction channel for Cl + C6 F5 H is estimated at (7.3 ± 5.7) × 10 −16 cm 3 molecule −1 s −1 . Establishment of the equilibrium between the adducts and the aromatic reactant + Cl occurs rapidly with equilibrium constants of K ([adduct]/[aromatic][Cl]) = (1.96 ± 0.11) × 10 −16 and (9.28 ± 0.11) × 10 −17 cm 3 molecule −1 for C6 F6 and C6 F5 H, respectively. Reaction of the adducts with O2 occurs slowly with estimated rate constants of <7 and <4 × 10 −18 cm 3 molecule −1 s −1 for C6 F6 –Cl and C6 F5 H–Cl, respectively. The rate constants for reaction of OH radicals with C6 F6 and C6 F5 H were determined to be (2.27 ± 0.49) × 10 −13 and (2.56 ± 0.62) × 10 −13 cm 3 molecule −1 s −1, respectively. UV and IR spectra of C6 F6 and C6 F5 H at 296 ± 1 K were collected and calibrated. Results are discussed in the context of available literature data for reactions of Cl atoms and OH radicals with halogenated aromatic compounds.