Flash photolysis kinetic study of reactions of the BrO radical with BrO and HO2

Bridier, Isabelle; Veyret, B.; Lesclaux, R.

doi:10.1016/0009-2614(93)85118-8

Cited by 51 publications

(63 citation statements)

References 15 publications

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“…Moreover in the presence of excess ozone, any bromine atoms produced in channel 1a of the BrO + BrO reaction are rapidly reconverted into BrO by reaction with ozone. Consequently, this channel has no effect on the observed BrO kinetics, and the observed BrO decay represents channel (1b) only, as has been verified in several previous studies: [4][5][6][7][8][9][10][11][12][13][14] However, as described by Rowley Furthermore, the reaction between Br atoms and ozone (3) has a positive temperature dependence 17 whereas that between Br and BrO accelerates rapidly at low temperatures. 26 Thus, experiments carried out in this work at low temperatures were performed with concentrations of ozone high enough to ensure that any Br atoms formed in channel 1a were consumed by ozone and not by BrO.…”

Section: Photolysis Of Br 2 In the Presence Of Osupporting

confidence: 62%

Kinetics and Mechanism of the BrO Self-Reaction: Temperature- and Pressure-Dependent Studies

et al. 1998

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The flash photolysis/UV absorption technique has been used to study the self-reaction of BrO radicals over the temperature range 222-298 K and the pressure range 100-760 Torr of N 2 or O 2 . Two chemical sources of BrO radicals were used: photolysis of Br 2 in the presence of excess ozone and photolysis of O 2 in the presence of excess Br 2 . The overall rate constant, k 1 , for the BrO self-reaction (defined by -d[BrO]/dt ) 2k 1 [BrO] 2 ) was found to be temperature and pressure independent at T g 250 K, with k 1 ) (2.88 ( 0.20) × 10 -12 cm 3 molecule -1 s -1 . At temperatures below 250 K, k 1 was found to be pressure dependent, due to the emergence of a new termolecular channel of the BrO self-reaction 1c, -1c forming the BrO dimer, Br 2 O 2 (BrO + BrO + M h Br 2 O 2 + M). Channel-specific rate constants were determined for the two bimolecular channels of the BrO self-reaction above 250 K, giving for (1a) (BrO + BrO f 2Br + O 2 ) k 1a ) (5.31 ( 1.17) × 10 -12 exp{(-211 ( 59)/T} cm 3 molecule -1 s -1 and for (1b) (BrO + BrO f Br 2 + O 2 ) k 1b ) (1.13 ( 0.47) × 10 -14 exp{(983 ( 111)/T} cm 3 molecule -1 s -1 . Below 250 K, the overall rate coefficient of the two bimolecular channels is reduced as the dimer forming channel emerges. At 235 and 222 K, rate constants for the formation (k 1c ) and decomposition (k -1c ) of Br 2 O 2 were recorded. Using the values for K 1c , ∆H r for reaction 1c was estimated as -58.6 ( 0.1 kJ mol -1 . A UV absorption spectrum attributed to Br 2 O 2 was also recorded over the wavelength range 300-390 nm. The cross section of the smooth Br 2 O 2 spectrum was found to be 1.2 × 10 -17 cm 2 molecule -1 at 320 nm. These results are rationalized in terms of a mechanism of the BrO self-reaction that shows competition, at low temperatures, between collisional quenching and unimolecular dissociation of an excited BrOOBr* intermediate. The rate constant for the reaction of oxygen atoms with molecular bromine was also determined in the course of these experiments [O + Br 2 f BrO + Br (5)], giving k 5 ) (5.12 ( 1.86) × 10 -13 exp{(989 ( 91)/T} cm 3 molecule -1 s -1 . All errors are 1σ. The atmospheric implications of these results are discussed.

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Section: Photolysis Of Br 2 In the Presence Of Osupporting

confidence: 62%

Kinetics and Mechanism of the BrO Self-Reaction: Temperature- and Pressure-Dependent Studies

et al. 1998

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“…HOBr + HCl f BrCl + H 2 O (heterogeneous) (8) BrCl + hν f Br + Cl (9) absorption cross-section estimates based on the assumption that the quantum yield for OH production at 355 and 510 nm are unity suggest that the lifetime of tropospheric HOBr will be shortened by a factor of 2 at the polar latitudes compared to recent estimates based on the absorption data for the UV bands alone.…”

Section: Introductionmentioning

confidence: 96%

Observation of a New Absorption Band of HOBr and Its Atmospheric Implications

et al. 1996

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A new absorption band of HOBr centered near 440 nm is detected by monitoring the yield of OH radicals as the wavelength of an excitation laser is scanned over the region from 440 to 650 nm. The band is believed to arise from excitation to a triplet state of HOBr, and although its peak absorption cross section is fairly modest, σ max ∼ 9 × 10 -21 cm 2 , its influence on determining the photochemical lifetime of HOBr is large due to its proximity to the peak of the solar actinic flux. Preliminary estimates suggest that inclusion of absorption by this new band system will shorten the photochemical lifetime of tropospheric HOBr in the polar regions by a factor of 2 compared to the recently recommended value based on the near-UV absorption bands alone.

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“…The kinetics of the self‐reaction of BrO

BrO + BrO \to Br + Br + {normalO}_{2},

BrO + BrO \to B {normalr}_{2} + {normalO}_{2},

BrO + BrO false(+ M false) \to B {normalr}_{2} {normalO}_{2} false(+ M false) .

has been studied very extensively in the past 5‐18 . All the available temperature‐dependent measurements indicate a negative temperature dependence of the total rate constant ( k 1 = k 1a + k 1b + k 1c ); however, the absolute values of k 1 differ by a factor of 1.6 7,9,13,15,18 .…”

Section: Introductionmentioning

confidence: 99%

Rate constant of the BrO + BrO reaction over the temperature range 220‐950 K

Bedjanian

2020

Int J of Chemical Kinetics

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The kinetics of the self‐reaction of BrO radicals has been studied over a wide temperature range (T = 220‐950 K) at 2 Torr total pressure of He using a low‐pressure flow reactor combined with a quadrupole mass spectrometer: BrO + BrO → 2Br + O2 (1a) and BrO + BrO → Br2 + O2 (1b). The overall rate constant for this reaction (defined by d[BrO]/dt = –2k1[BrO]2) was found to be k1 = k1a +k1b = (1.32 ± 0.09) × 10−12 exp(182 ± 22/T) cm3 molecule−1 s−1 at T = 220‐950 K (where the uncertainties represent precision at the 2σ level). The channel‐specific rate constant for the Br2 + O2 forming channel (1b) was determined at T = 220‐450 K: k1b = (2.83 ± 0.35) × 10−13 exp(34 ± 36/T) cm3 molecule−1 s−1 (with 2σ uncertainties). As a result of the comparative analysis of the present data and those from the previous studies, the following Arrhenius expressions are recommended from the present work: k1 = 1.4 × 10−12 exp(200/T) at T = 220‐950 K (independent of pressure at least for T ≥ 250 K) and k1b = 3.2 × 10−13 exp(34/T) cm3 molecule−1 s−1 at T = 220‐450 K and total pressure of 2 Torr, with a conservative estimate of uncertainty of 25%, independent of temperature.

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Flash photolysis kinetic study of reactions of the BrO radical with BrO and HO2

Cited by 51 publications

References 15 publications

Kinetics and Mechanism of the BrO Self-Reaction: Temperature- and Pressure-Dependent Studies

Kinetics and Mechanism of the BrO Self-Reaction: Temperature- and Pressure-Dependent Studies

Observation of a New Absorption Band of HOBr and Its Atmospheric Implications

Rate constant of the BrO + BrO reaction over the temperature range 220‐950 K

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