TY - JOUR
T1 - Kinetics and product yields in the heterogeneous reactions of HOBr with ice surfaces containing NaBr and NaCl
AU - Huff, Amy K.
AU - Abbatt, Jonathan P.D.
PY - 2002/5/30
Y1 - 2002/5/30
N2 - 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.
AB - 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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U2 - 10.1021/jp014296m
DO - 10.1021/jp014296m
M3 - Article
AN - SCOPUS:0037198833
SN - 1089-5639
VL - 106
SP - 5279
EP - 5287
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 21
ER -