title: Reaction of iodine atoms with submicrometer squalane and squalene droplets: mechanistic insights into heterogeneous reactions.
abstract: The gas-phase reaction of iodine atoms with hydrocarbon molecules is energetically unfavorable, and there is no direct evidence for iodinated product formation by either H abstraction or I addition reactions at ambient temperature. Here we consider the possible heterogeneous reaction of I atoms with submicrometer droplets composed of a saturated alkane, squalane (Sq), and an unsaturated alkene, squalene (Sqe). The investigations are performed in an atmospheric pressure photochemical flow tube reactor in conjunction with a vacuum ultraviolet photoionization aerosol mass spectrometer and a scanning mobility particle sizer. Squalane, a branched alkane, is unreactive toward I atoms within the signal-to-noise, and an upper limit of the effective reactive uptake coefficient is estimated to be γI(Sq) ≤ 8.58 × 10(–7). In contrast, the reaction of I atoms with unsaturated submicrometer squalene droplets results in observable iodinated squalene products. The effective reactive uptake coefficient of I atom with squalene particles is determined to be γI(Sqe) = (1.20 ± 0.52) × 10(–4) at an average I concentration of 1.5 × 10(14) molecules·cm(–3).
authors.affiliation: Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Denisia M
authors.initials: DM
authors.lastname: Popolan-Vaida
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Wilson
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Leone
mesh_terms: D000336:Aerosols / Q000737:chemistry; D007455:Iodine / Q000737:chemistry*; D007700:Kinetics; D013058:Mass Spectrometry; D015394:Molecular Structure; D010782:Photolysis; D013185:Squalene / Q000031:analogs & derivatives* / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D000336:Aerosols; D013185:Squalene; D007455:Iodine; C019556:squalane