Kinetics and product yields in the heterogeneous reactions of HOBr with ice surfaces containing NaBr and NaCl

Amy Kathleen Huff, Jonathan P.D. Abbatt

Research output: Contribution to journalArticle

47 Citations (Scopus)

Abstract

The heterogeneous reactions of HOBr with ice surfaces formed by freezing sodium halide solutions were studied using a coated-wall, low-pressure flow tube coupled to a quadrupole mass spectrometer. Experiments were conducted at 233 and 248 K with films containing bromide, chloride, or a mixture of the two, and with HOBr gas-phase concentrations of about 1012 molecules/cm3. Gas-surface uptake coefficients and product yields are presented for a range of halide and hydrogen ion concentrations. Compared to analogous reactions with HOCl, HOBr reactions were slower than expected with a maximum uptake coefficient of approximately 0.01. At both 233 and 248 K, gas-phase Br2 was formed exclusively from bromide-only films and only BrCl was formed from chloride films. When both ions were present, BrCl was the sole gas-phase product observed at 233 K, while both gas-phase Br2 and BrCl were formed at 248 K. The relative yields of the gas-phase products depend on the temperature, composition, and acidity of halide-ice surfaces. A mechanism consistent with the observations involves initial formation of a HOBr·X- complex, where X- is either chloride or bromide, followed by reaction of the complex with a proton. For this reason, reaction probabilities for the formation of BrCl or Br2 were higher on acidified films than on films formed pH-neutral solutions. The atmospheric implications of these results are discussed.

Original languageEnglish (US)
Pages (from-to)5279-5287
Number of pages9
JournalJournal of Physical Chemistry A
Volume106
Issue number21
DOIs
StatePublished - May 30 2002

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Ice
ice
Gases
vapor phases
Kinetics
kinetics
halides
products
bromides
Bromides
chlorides
Chlorides
pH
coefficients
hydrogen ions
ion concentration
acidity
freezing
mass spectrometers
Pipe flow

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry

Cite this

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title = "Kinetics and product yields in the heterogeneous reactions of HOBr with ice surfaces containing NaBr and NaCl",
abstract = "The heterogeneous reactions of HOBr with ice surfaces formed by freezing sodium halide solutions were studied using a coated-wall, low-pressure flow tube coupled to a quadrupole mass spectrometer. Experiments were conducted at 233 and 248 K with films containing bromide, chloride, or a mixture of the two, and with HOBr gas-phase concentrations of about 1012 molecules/cm3. Gas-surface uptake coefficients and product yields are presented for a range of halide and hydrogen ion concentrations. Compared to analogous reactions with HOCl, HOBr reactions were slower than expected with a maximum uptake coefficient of approximately 0.01. At both 233 and 248 K, gas-phase Br2 was formed exclusively from bromide-only films and only BrCl was formed from chloride films. When both ions were present, BrCl was the sole gas-phase product observed at 233 K, while both gas-phase Br2 and BrCl were formed at 248 K. The relative yields of the gas-phase products depend on the temperature, composition, and acidity of halide-ice surfaces. A mechanism consistent with the observations involves initial formation of a HOBr·X- complex, where X- is either chloride or bromide, followed by reaction of the complex with a proton. For this reason, reaction probabilities for the formation of BrCl or Br2 were higher on acidified films than on films formed pH-neutral solutions. The atmospheric implications of these results are discussed.",
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Kinetics and product yields in the heterogeneous reactions of HOBr with ice surfaces containing NaBr and NaCl. / Huff, Amy Kathleen; Abbatt, Jonathan P.D.

In: Journal of Physical Chemistry A, Vol. 106, No. 21, 30.05.2002, p. 5279-5287.

Research output: Contribution to journalArticle

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