FTIR study of the DMS/NO2/I2/N2 photolysis system: The reaction of IO radicals with DMS

A steady-state system involving the photolysis of NO₂ in an excess of I₂ as a source of IO radicals has been used to study the reaction IO + DMS in 760 Torr N₂ at 296 K. IO radicals were found to react rapidly with DMS, one molecule of DMSO being produced for each molecule of DMS consumed. Numerical analysis of the experimental results yielded a rate constant of (3.0 ± 1.5) × 10^?11 cm³ s^?1 for the reaction IO + DMS → DMSO + I.     

Kinetic study of the reaction of BrO radicals with dimethylsulfide

The kinetics and mechanism of the reaction of BrO with dimethylsulfide (DMS) have been studied by the mass spectrometric discharge-flow method in the temperature range (233–320) K and at a total pressure around 1 torr. The temperature dependence of the reaction rate constant k₁ = (1.5 ± 0.4) × 10⁻¹⁴ exp [(845 ± 175)/T] cm³ molecule⁻¹s⁻¹ has been determined under pseudo-first-order conditions in excess of DMS over BrO radicals. Mass spectrometric calibration of the reaction product dimethylsulfoxide (DMSO) allowed for a determination of the branching ratio of (0.94 ± 0.11) for the DMSO forming channel. These data indicate that the reaction is likely to proceed through a channel involving a long-lived intermediate: BrO + CH₃SCH₃ →[CH₃S(OBr)CH₃]* → CH₃S(O)CH₃ + Br. The atmospheric application of the data is briefly discussed. © 1996 John Wiley & Sons, Inc.     

FT‐IR kinetic and product study of the Br‐initiated oxidation of dimethyl sulfide

An FT‐IR kinetic and product study of the Br‐atom‐initiated oxidation of dimethyl sulfide (DMS) has been performed in a large‐volume reaction chamber at 298 K and 1000‐mbar total pressure as a function of the bath gas composition (N₂ + O₂). In the kinetic investigations using the relative kinetic method, considerable scatter was observed between individual determinations of the rate coefficient, suggesting the possibility of interference from secondary chemistry in the reaction system involving dimethyl sulfoxide (DMSO) formation. Despite the experimental difficulties, an overall bimolecular rate coefficient for the reaction of Br atoms with DMS under atmospheric conditions at 298 K of ≤1 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ can be deduced. The major sulfur products observed included SO₂, CH₃SBr, and DMSO. The kinetic observations in combination with the product studies under the conditions employed are consistent with rapid addition of Br atoms to DMS forming an adduct that mainly re‐forms reactants but can also decompose unimolecularly to form CH₃SBr and CH₃ radicals. The observed formation of DMSO is attributed to reactions of BrO radicals with DMS rather than reaction of the Br–DMS adduct with O₂ as has been previously speculated and is thought to be responsible for the variability of the measured rate coefficient. The reaction CH₃O₂ + Br → BrO + CH₃O is postulated as the source of BrO radicals. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 883–893, 1999     

Kinetics of reactions of OBrO with NO,O3, OClO,and ClO at 240–350 K

Kinetics for the reactions of OBrO with NO, O₃, OClO, and ClO at 240–350 K were investigated using the technique of discharge flow coupled with mass spectrometry. The Arrhenius expression for the OBrO reaction with NO was determined to be k₁ = (2.37 ± 0.96) × 10^?13 exp[(607 ± 63)/T] cm³ molecule^?1 s^?1. The reactions of OBrO with O₃, OClO, and ClO are slow chemical processes at 240–350 K. Upper limit rate constants for the OBrO reactions with O₃, OClO, and ClO at 240–350 K were estimated to be k₂ < 5.0 × 10^?15 cm³ molecule^?1 s^?1, k₃ < 6.0 × 10^?14 cm³ molecule^?1 s^?1, and k₄ < 1.5 × 10^?13 cm³ molecule^?1 s^?1, respectively. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 430–437, 2002     

Kinetics of the reactions of the IO radical with dimethyl sulfide,methanethiol, ethylene,and propylene

The reactions of IO radicals with CH₃SCH₃, CH₃SH, C₂H₄, and C₃H₆ have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH₃SCH₃ → products (1): k₁ = (1.5 ± 0.2) × 10^?14; IO + CH₃SH → products (2): k₂ = (6.6 ± 1.3) × 10^?16; IO + C₂H₄ →products (3): k₃ < 2 × 10^?16; IO + C₃H₆ → products (4): k₄ < 2 × 10^?16 (units are cm³ molecule^?1 s^?1). CH₃S(O)CH₃ and HOI were found as products of reactions (1) and (2), respectively. The present lower value of k₁ compared to our previous determination is discussed.     

Kinetics of the reactions of Cl(2PJ) and Br(2P3/2) with O3

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the important stratospheric reactions Cl(²P_J) + O₃ → ClO + O₂ and Br(²P_3/2) + O₃ → BrO + O₂ as a function of temperature. The temperature dependence observed for the Cl(²P_J) + O₃ reaction is nonArrhenius, but can be adequately described by the following two Arrhenius expressions (units are cm³ molecule^?1 s^?1, errors are 2σ and represent precision only): ??₁(T) = (1.19 ± 0.21) × 10^?11 exp [(?33 ± 37)/T] for T = 189–269K and ??₁(T) = (2.49 ± 0.38) × 10^?11 exp[(?233 ± 46)/T] for T = 269–385 K. At temperatures below 230 K, the rate coefficients determined in this study are faster than any reported previously. Incorporation of our values for ??₁(T) into stratospheric models would increase calculated ClO levels and decrease calculated HCl levels; hence the calculated efficiency of ClO_x catalyzed ozone destruction would increase. The temperature dependence observed for the (²P_3/2) + O₃ reaction is adequately described by the following Arrhenius expression (units are cm³ molecule^?1 s^?1, errors are 2σ and represent precision only): ??₂(T) = (1.50 ± 0.16) × 10^?1 exp[(?775 ± 30)/T] for T = 195–392 K. While not in quantitative agreement with Arrhenius parameters reported in most previous studies, our results almost exactly reproduce the average of all earlier studies and, therefore, will not affect the choice of ??₂(T) for use in modeling stratospheric BrO_x chemistry.     

Laser magnetic resonance spectroscopy of ClO and kinetic studies of the reactions of ClO with NO and NO2

Far-infrared rotational transitions in ClO(X²∏_3/2, υ = 0) have been observed using laser magnetic resonance (LMR) with an optically pumped spectrometer. Five observed transitions at wavelengths between 444 and 713 µm have been compared with values predicted with spectroscopic constants from the literature. LMR detection of ClO has been used to study its reactions with NO and NO₂ in a discharge flow system under pseudo-first-order conditions for ClO. The measured rate constants are k(ClO + NO) = (7.1 ± 1.4) × 10^?12 exp[(270 ± 50)/T] cm³/molec·s for the temperature range of 202 < T < 393 K; k(ClO + NO₂ + M) = (2.8 ± 0.6) × 10^?33 exp[(1090 ± 80)/T] cm⁶/molec²·s (M = He, 250 < T < 387 K), (3.5 ± 0.6) × 10^?33 exp[(1180 ± 80)/T] (M = O₂, 250 < T < 416 K), and (2.09 ± 0.3) × 10^?31 (M = N₂, T = 297 K). All measurements were made at low pressures, between 0.6 and 6.6 torr. These results are compared with those from other studies.     

Kinetics of the reactions of CH3O with Br and BrO at 298 K

A discharge flow reactor coupled to a laser-induced fluorescence (LIF) detector and a mass spectrometer was used to study the kinetics of the reactions CH₃O+Br→products (1) and CH₃O+BrO→products (2). From the kinetic analysis of CH₃O by LIF in the presence of an excess of Br or BrO, the following rate constants were obtained at 298 K: k₁=(7.0±0.4)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k₂=(3.8±0.4)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The data obtained are useful for the interpretation of other laboratory studies of the reactions of CH₃O₂ with Br and BrO. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 249–255, 1998.     

Kinetic studies of free radical reactions by mass spectrometry. II. The reactions of SO + ClO,SO + OClO and SO + BrO

The rates of several novel elementary reactions involving ClO, BrO and SO free radicals in their ground states were studied in a discharge-flow system at 295 K, using mass spectrometry. The rate constant k₂ was determined from the decay of SO radicals in the presence of excess ClO radicals: The SO + OClO overall reaction has a complex mechanism, with the primary step having a rate constant k₅ equal to (1.9 ± 0.7) × 10^?12 cm³ sec^?1: A lower limit for the rate constant of the rapid reaction of SO radicals with BrO radicals was determined:      

Kinetics of the reactions of acenaphthene and acenaphthylene and structurally-related aromatic compounds with OH and NO3 radicals,N2O5 and O3 at 296 ± 2 K

The kinetics of the atmospherically important gas-phase reactions of acenaphthene and acenaphthylene with OH and NO₃ radicals, O₃ and N₂O₅ have been investigated at 296 ± 2 K. In addition, rate constants have been determined for the reactions of OH and NO₃ radicals with tetralin and styrene, and for the reactions of NO₃ radicals and/or N₂O₅ with naphthalene, 1- and 2-methylnaphthalene, 2,3-dimethylnaphthalene, toluene, toluene-α,α,α-d₃ and toluene-d₈. The rate constants obtained (in cm³ molecule^?1 s^?1 units) at 296 ± 2 K were: for the reactions of O₃; acenaphthene, <5 × 10^?19 and acenaphthylene, ca. 5.5 × 10^?16; for the OH radical reactions (determined using a relative rate method); acenaphthene, (1.03 ± 0.13) × 10^?10; acenaphthylene, (1.10 ± 0.11) × 10^?10; tetralin, (3.43 ± 0.06) × 10^?11 and styrene, (5.87 ± 0.15) × 10^?11; for the reactions of NO₃ (also determined using a relative rate method); acenaphthene, (4.6 ± 2.6) × 10^?13; acenaphthylene, (5.4 ± 0.8) × 10^?12; tetralin, (8.6 ± 1.3) × 10^?15; styrene, (1.51 ± 0.20) × 10^?13; toluene, (7.8 ± 1.5) × 10^?17; toluene-α,α,α-d₃, (3.8 ± 0.9) × 10^?17 and toluene-d₈, (3.4 ± 1.9) × 10^?17. The aromatic compounds which were observed to react with N₂O₅ and the rate constants derived were (in cm³ molecule^?1 s^?1 units): acenaphthene, 5.5 × 10^?17; naphthalene, 1.1 × 10^?17; 1-methylnaphthalene, 2.3 × 10^?17; 2-methylnaphthalene, 3.6 × 10^?17 and 2,3-dimethylnaphthalene, 5.3 × 10^?17. These data for naphthylene and the alkylnaphthalenes are in good agreement with our previous absolute and relative N₂O₅ reaction rate constants, and show that the NO₃ radical reactions with aromatic compounds proceed by overall H-atom abstraction from substituent-XH bonds (where X = C or O), or by NO₃ radical addition to unsaturated substituent groups while the N₂O₅ reactions only occur for aromatic compounds containing two or more fused six-membered aromatic rings.     

Gas-phase reactions of 1,4-benzodioxan, 2,3-dihydrobenzofuran,and 2,3-benzofuran with OH radicals and O3

The kinetics of the gas-phase reactions of 1,4-benzodioxan, 2,3-dihydrobenzofuran, and 2,3-benzofuran with OH radicals and O₃ have been studied at 298 ± 2 K and atmospheric pressure of air and the products have also been investigated. 1,4-Benzodioxan and 2,3-dihydrobenzofuran were chosen as volatile model compounds for dibenzo-p-dioxin and dibenzofuran, respectively. The rate constants, or upper limits thereof, for the O₃ reactions were (in cm³ molecule^?1 s^?1 units): 1,4-benzodioxan, <1.2 × 10^?20; 2,3-dihydrobenzofuran, <1 × 10^?19; and 2,3-benzofuran, (1.83 ± 0.21) × 10^?18. Using a relative rate method, the rate constants for the OH radical reactions (in cm³ molecule^?1 s^?1 units) were: 1,4-dibenzodioxan, (2.52 ± 0.38) × 10^?11; 2,3-dihydrobenzofuran, (3.66 ± 0.56) × 10^?11; and 2,3-benzofuran, (3.73 ± 0.74) × 10^?11. Salicylaldehyde was observed as a product of the OH radical-initiated and O₃ reactions of 2,3-benzofuran, with measured formation yields of 0.26 ± 0.05 and 0.13 ± 0.07, respectively.     

A kinetic study of the reaction of fluorine atoms with CH3F,CH3Cl,CH3Br,CF2H2, CO,CF3H,CF3CHCl2, CF3CH2F,CHF2CHF2, CF2ClCH3, CHF2CH3, and CF3CF2H at 295 ± 2 K

A variety of relative and absolute techniques have been used to measure the reactivity of fluorine atoms with a series of halogenated organic compounds and CO. The following rate constants were derived, in units of cm³ molecule^?1 s^?1: CH₃F, (3.7 ± 0.8) × 10^?11, CH₃Cl, (3.3 ± 0.7) × 10^?11; CH₃Br, (3.0 ± 0.7) × 10^?11; CF₂H₂, (4.3 ± 0.9) × 10^?12; CO, (5.5 ± 1.0) × 10^?13 (in 700 torr total pressure of N₂ diluent); CF₃H, (1.4 ± 0.4) × 10^?13; CF₃CCl₂H (HCFC-123), (1.2 ± 0.4) × 10^?12; CF₃CFH₂ (HFC-134a), (1.3 ± 0.3) × 10^?12, CHF₂CHF₂ (HFC-134), (1.0 ± 0.3) × 10^?12; CF₂ClCH₃ (HCFC-42b), (3.9 ± 0.9) × 10^?12, CF₂HCH₃ (HFC-152a), (1.7 ± 0.4) × 10^?11; and CF₃CF₂H (HFC-125), (3.5 ± 0.8) × 10^?13. Quoted errors are statistical uncertainties (2σ). For rate constants derived using relative rate techniques, an additional uncertainty has been added to account for potential systematic errors in the reference rate constants used. Experiments were performed at 295 ± 2 K. Results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFCs and HFCs. © 1993 John Wiley & Sons, Inc.     

A relative rate study of the reaction of bromine atoms with a variety of organic compounds at 295 K

The relative rate technique has been used to determine rate constants for the reaction of bromine atoms with a variety of organic compounds. Decay rates of the organic species were measured relative to i-butane or acetaldehyde or both. Using rate constants of 1.74 × 10^?15 and 3.5 × 10^?12 cm³ molecule^?1 s^?1 for the reaction of Br with i?butane and acetaldehyde respectively, the following rate constants were derived, in units of cm³ molecule^?1 s^?1: 2, 3?dimethylbutane, (6.40 ± 0.77) × 10^?15; cyclopentane, (1.16 ± 0.18) × 10^?15, ethene, (≤2.3 × 10^?13); propene, (3.85 ± 0.41) × 10^?12; trans-2-butene, (9.50 ± 0.76) × 10^?12, acetylene, (5.15 ± 0.19) × 10^?15; and propionaldehyde, (9.73 ± 0.91) × 10^?12. Quoted errors represent 2σ and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The results are discussed with respect to the mechanisms of these reactions and their utility in serving as a laboratory source of alkyl and alkyl peroxy radicals.     

Rate constants for the reactions of Br atoms with a series of alkanes,alkenes, and alkynes in the presence of O2

Rate constants of Br atom reactions have been determined using a relative kinetic method in a 20 l reaction chamber at total pressures between 25 and 760 torr in N₂ + O₂ diluent over the temperature range 293–355 K. The measured rate constants for the reactions with alkynes and alkenes showed dependence upon temperature, total pressure, and the concentration of O₂ present in the reaction system. Values of (6.8 ± 1.4) × 10^?15, (3.6 ± 0.7) × 10^?14, (1.5 ± 0.3) × 10^?12, (1.6 ± 0.3) × 10^?13, (2.7 ± 0.5) × 10^?12, (3.4 ± 0.7) × 10^?12, and (7.5 ± 1.5) × 10^?12 (units: cm³ s^?1) have been obtained as rate constants for the reactions of Br with 2,2,4-trimethylpentane, acetylene, propyne, ethene, propene, 1-butene, and trans-2-butene, respectively, in 760 torr of synthetic air at 298 K with respect to acetaldehyde as reference, k = 3.6 × 10^?12 cm³ s^?1. Formyl bromide and glyoxal were observed as primary products in the reaction of Br with acetylene in air which further react to form CO, HBr, HOBr, and H₂O₂. Bromoacetaldehyde was observed as an primary product in the reaction of Br with ethene. Other observed products included CO, CO₂, HBr, HOBr, BrCHO, bromoethanol, and probably bromoacetic acid.     

Selected rate constants for H,O, N,and Cl atoms with substrates at room temperatures

Rate constants for H + Cl₂, H + CH₃CHO, H + C₃H₄, O + C₃H₆, O + CH₃CHO, and Cl + CH₄ have been measured at room temperature by the discharge flow—resonance fluorescence technique. The results are (1.6 ± 0.1) × 10^?11, (9.8 ± 0.8) × 10 ^?14, (6.3 ± 0.4) × 10^{?13) (2.00 torr He), (3.95 ± 0.41) × 10?12, (4.9 ± 0.5) × 10|su?13} and (1.08 ± 0.07) × 10^?13, respectively, all in units of cm³ molecule^?1 s^?1. Also N atom reactions with C₂H₂, C₂H₄, C₃H₄, and C₃H₆ were studied but in no case was there an appreciable rate constant. These results are compared to previous studies.     

Kinetics of the reactions of naphthalene, 2-methylnaphthalene,and 2,3-dimethylnaphthalene with OH radicals and with O3 at 295 ± 1 K

The kinetics of the gas-phase reactions of naphthalene, 2-methylnaphthalene, and 2,3-dimethylnaphthalene with O₃ and with OH radicals have been studied at 295 ± 1 K in one atmosphere of air. Upper limit rate constants for the O₃ reactions of <3 × 10^?19, <4 × 10^?19, and <4 × 10^?19 cm³ molecule^?1 s^?1 were obtained for naphthalene, 2-methylnaphthalene, and 2,3-dimethylnaphthalene, respectively. For the OH radical reactions, rate constants of (in units of 10^?11 cm³ molecule^?1 s^?1) 2.59 ± 0.24, 5.23 ± 0.42, and 7.68 ± 0.48 were determined for naphthalene, 2±methylnaphthalene, and 2,3-dimethylnaphthalene, respectively. These data show that under atmospheric conditions these naphthalenes will react mainly with the OH radical, with life-times due to this reaction ranging from ca. 11 h for naphthalene to ca. 4 h for 2,3-dimethylnaphthalene.     

Zur kristallchemischen Ähnlichkeit von Aurid- und Halogenid-Ionen

On the Crystal Chemical Similarity of Auride and Halide Anions The crystallographic properties of the aurides M₃AuO and the alkalimetal halide oxides M₃XO (M = K, Rb, Cs; × = Br, I) are compared. Rb₃BrO, Rb₃IO, Cs₃BrO, and Cs₃IO have been prepared and characterized for the first time: Rb₃BrO (a = 5.465(1) Å) crystallizes as a cubic anti perovskite, Cs₃BrO (a = 7.800(6), c = 7.122(6) Å) and Cs₃IO (a = 8.056(3), c = 7.168(3) Å) as hexagonal anti perovskites, Rb₃IO (a = 7.889(1), c = 19.640(1) Å) as a hexagonal anti BaTiO₃ type. The analysis of bond lengths, molar volumes and the systematic of the crystal structures leeds to the conclusion, that the crystallographic properties of auride- and bromide anions are similar. The radius of the Au^? has been found to be 2.2 Å (KZ 12).     

The temperature dependence of the bimolecular channels of the ClO + ClO reaction over the range T = 298–323 K

The bimolecular channels of the ClO self‐reaction, although negligible under stratospheric conditions, become significant above ambient temperature. The kinetics of two of the three bimolecular channels of the ClO self‐reaction, ClO + ClO → Cl₂ + O₂ (1b) and ClO + ClO → OClO + Cl (1d), were studied at T = 298–323 K and at ambient pressure (p_atm≈ 760 ± 10 Torr). Radicals were generated via laser photolysis and monitored using UV absorption spectroscopy. The inclusion of charge‐coupled device (CCD) detection allowed broadband monitoring of the radicals of interest along with the temporal resolution of their concentrations. Accurate and unequivocal quantification of the structured absorbers (ClO and OClO) was obtained via differential fitting procedures. The Arrhenius expressions obtained are k_1b = 2.9_?1.8^+4.4 × 10^?14exp[?(283 ± 282)/T] cm³ molecule^?1 s^?1 and k_1d = 7.2_?6.1⁺³⁹ × 10^?15exp[?(225 ± 574)/T] cm³ molecule^?1 s^?1, where the errors are 1σ. The temperature dependences obtained in this work for both channels monitored are considerably less pronounced than those reported by Nickolaisen et al. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 386–397, 2012     

Rate coefficients and ClO radical yields in the reaction of O(1D) with CClF2CCl2F,CCl3CF3, CClF2CClF2, and CCl2FCF3

Rate coefficients, k, and ClO radical product yields, Y, for the gas‐phase reaction of O(¹D) with CClF₂CCl₂F (CFC‐113) (k₂), CCl₃CF₃ (CFC‐113a) (k₃), CClF₂CClF₂ (CFC‐114) (k₄), and CCl₂FCF₃ (CFC‐114a) (k₅) at 296 K are reported. Rate coefficients for the loss of O(¹D) were measured using a competitive reaction technique, with n‐butane (n‐C₄H₁₀) as the reference reactant, employing pulsed laser photolysis production of O(¹D) combined with laser‐induced fluorescence detection of the OH radical temporal profile. Rate coefficients were measured to be k₂ = (2.33 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.61 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₄ = (1.42 ± 0.25) × 10^?10 cm³ molecule^?1 s^?1, and k₅ = (1.62 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1. ClO radical product yields for reactions (2)–(5) were measured using pulsed laser photolysis combined with cavity ring‐down spectroscopy to be 0.80 ± 0.10, 0.79 ± 0.10, 0.85 ± 0.12, and 0.79 ± 0.10, respectively. The quoted errors in k and Y are at the 2σ (95% confidence) level and include estimated systematic errors. © 2011 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America

Int J Chem Kinet 43: 393–401, 2011     

Rate constants for the reactions of O3 and OH radicals with a series of alkynes

Rate constants for the reactions of O₃ and OH radicals with acetylene, propyne, and 1-butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O₃ with acetylene, propyne, and 1-butyne were (7.8 ± 1.2) × 10^?21 cm³/molecule · s, (1.43 ± 0.15) × 10^?20 cm³/molecule · s, and (1.97 ± 0.26) × 10^?20 cm³/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10^?12 cm³/molecule · s, were determined to be (8.8 ± 1.4) × 10^?13 cm³/molecule · s, (6.21 ± 0.31) × 10^?12 cm³/molecule · s, and (8.25 ± 0.23) × 10^?12 cm³/molecule · s for acetylene, propyne, and 1-butyne, respectively. These data are discussed and compared with the available literature rate constants.