Rate constant and products of the reaction CS2 + OH in the presence of O2

The reaction of OH radicals with CS₂ has been investigated by the application of Fourier transform infrared spectroscopy using both photolytic and nonphotolytic competitive techniques in a 420-L reaction chamber at different pressures over the temperature range of 264–293 K. The measured effective rate constant was found to be dependent on total pressure, temperature, and the mole fraction of O₂ present in the system. The products of the reaction were found to be COS and SO₂ with one molecule of each being formed for every reacted CS₂. A value of (2.7 ± 0.6) × 10^?12 cm³/molecule·s was obtained as effective rate constant for the reaction at 293 K in 760 torr of synthetic air.     

Reaction rate constant of SO3 + CH3OH in the gas phase

The reaction rates of SO₃ with CH₃OH in He were measured at total pressures of 0.7–1.6 torr in flow tubes. The concentration of SO₃ was monitored by the SO₂* fluorescence from excitation of SO₃ at 147 nm. The reaction rate constant of SO₃ + CH₃OH in the gas phase is determined to be (1.17 ± 0.16) × 10^?13 cm³ molec^?1 s^?1 at room temperature.     

An absolute and relative rate study of the reaction of oh radicals with dimethyl sulfide

The gas phase reaction of OH radicals with dimethyl sulfide (CH₃SCH₃, DMS) has been studied using both an absolute and a relative technique at 295 ± 2 K and a total pressure of 1 atm. The absolute rate technique of pulse radiolysis combined with kinetic spectroscopy was applied. Using this technique a rate constant of (3.5 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1 was obtained. For the relative rate method, rate constants for the reaction of OH with DMS were found to increase with increasing concentrations of added NO. These results are compared with the large body of kinetic and mechanistic data previously reported in the literature.     

Kinetics of the reactions of atomic chlorine with methanol and the hydroxymethyl radical with molecular oxygen at 298 K

The rate constants for the reactions Cl + CH₃OD → CH₂OD + HCl (1) and CH₂OH + O₂ → HO₂ + H₂CO (2) have been determined in a discharge flow system near 1 torr pressure with detection of radical and molecular species using collision-free sampling mass spectrometry. The rate constant k₁, determined from the decay of CH₃OD in the presence of excess Cl, is (5.1 ± 1.0) × 10^?11 cm³ s^?1. This is in reasonable agreement with the only previous measurement of k₁. The CH₂OH radical was produced by reaction (1) and its reaction with O₂ was studied by monitoring the decay of the CH₂OH radical in the presence of excess O₂. The result is k₂ = (8.6 ± 2.0) × 10^?12 cm³ s^?1. Previous estimates of k₂ have differed by nearly an order of magnitude, and our value for k₂ supports the more recent high values.     

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.     

FTIR spectroscopic study of the Cl- and Br-atom initiated oxidation of ethene

The reaction mechanism of the halogen (Cl and Br)-atom initiated oxidation of C₂H₄ was studied using the long path FTIR spectroscopic method in 700 torr of air at 296 ± 2 K. Among the major halogen-containing products were X? CH₂CHO, X? CH₂CH₂OH, and X? CH₂CH₂OOH (X = Cl or Br) which were shown to be formed via the self-reaction of the X? CH₂CH₂OO radicals, i.e., 2X? CH₂CH₂OO → 2X? CH₂CH₂O + O₂; (a) 2X? CH₂CH₂OO → X? CH₂CHO + X? CH₂CH₂OH + O₂ and (b) followed by X? CH₂CH₂O + O₂ → X? CH₂CHO + HO₂ and X? CH₂CH₂OO + HO₂ → X? CH₂CH₂OOH + O₂. From the observed yields of X? CH₂CHO and X? CH₂CH₂OH the branching ratios for reactions (a) and (b) were determined to be k_a/k_b = 1.35 ± 0.07(2σ) for both X = Cl and Br. In addition, the O₂-dependence of the rate constant for the Br + C₂H₄ reaction was determined by the relative rate technique as a function of O₂ partial pressure from 140 to 700 torr at 700 torr total pressure of N₂/O₂ diluent. Rate constants for the reactions of Cl-atoms with Cl-CH₂CHO and Br-atoms with Br-CH₂CHO were also determined to be [4.3 ± 0.2(2sigma;)] × 10^?11 and less than or equal to [1.83 ± 0.11(2σ)] × 10^?13 cm³ molecule^?1 s^?1, respectively.     

FTIR studies of the kinetics and mechanism for the reaction of Cl atom with formylchloride

The rate constant for the reaction Cl + CHClO → HCl + CClO was determined from relative decay rates of CHClO and CH₃Cl inthe photolysis of mixtures containing Cl₂ (～1 torr), CH₃Cl (～1 torr), and O₂ (～0.1 torr) in 700 torr N₂. In such mixtures CHClO was generated in situ as a principal product prior to complete consumption of O₂. The value of k(Cl + CHClO)/k(Cl + CH₃Cl) = 1.6 ± 0.2(3σ) combined with the literature value of k(Cl + CH₃Cl) = 4.9 × 10^?13 cm³/molecule sec gives k(Cl + CHClO) = 7.8 × 10^?13 cm³/molecule sec at 298 ± 2 K, in excellent agreement with a previous value of (7.9 ± 1.5) × 10^?13 cm³/molecule sec determined by Sanhueza and Heicklen [J. Phys. Chem., 79 , 7 (1975)]. Thus this reaction is approximately 100 times slower than the corresponding reactions of aldehydes and alkanes with comparable C? H bond energies (≤95 kcal/mol).     

FTIR study of the Cl-atom initiated oxidation of methylglyoxal

The kinetics and mechanism of Cl-atom initiated reactions of CH₃C(O)CHO were studied using the FTIR detection method in the photolysis (λ < 300 nm) of Cl₂? CH₃C(O)CHO mixtures in 700 torr of N₂? O₂ diluent at 298 ± 2 K. The observed product distribution over the O₂ pressure range from 0–700 torr, combined with relative rate measurements, provided evidence that: (1) the primary step is Cl + CH₃C(O)CHO → HCl + CH₃C(O)CO with a rate constant of (4.8 ± 1.1) × 10^?11 cm³ molecule^?1 s^?1; and (2) the predominant fate of the primary radical CH₃C(O)CO under atmospheric conditions is unimolecular dissociation to CH₃C(O) radicals and CO, rather than O₂-addition to yield the corresponding carbonylperoxy radical CH₃C(O)C(O)OO.     

An ftir study of the reaction between nitrogen dioxide and alcohols

The reaction 2NO₂ + ROH = RONO + HNO₃ (R = CH₃ or C₂H₅) has been studied using the FTIR method at reactant pressures from 0.1 to 1.0 torr at 25°C. The termolecular rate constant for the forward reaction was determined to be (5.7 ± 0.6) × 10^?37 cm⁶/molec²·s for CH₃OH and (5.7 ± 0.8) × 10^?37 cm⁶/molec²·s for C₂H₅OH, that is, d[RONO]/dt = k[NO₂]²[ROH]. The corresponding equilibrium constants were measured as 1.36 ± 0.06 and 0.550 ± 0.025 torr^?1, respectively. These results are consistent with those of a previous study based on the NO₂ decay measurements at reactant pressures from 1 to 10 torr.     

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.     

Rate coefficients for the gas‐phase reactions of OH radicals with methylbutenols at 298 K

The relative‐rate method has been used to determine the rate coefficients for the reactions of OH radicals with three C₅ biogenic alcohols, 2‐methyl‐3‐buten‐2‐ol (k₁), 3‐methyl‐3‐buten‐1‐ol (k₂), and 3‐methyl‐2‐buten‐1‐ol (k₃), in the gas phase. OH radicals were produced by the photolysis of CH₃ONO in the presence of NO. Di‐n‐butyl ether and propene were used as the reference compounds. The absolute rate coefficients obtained with the two reference compounds agreed well with each other. The O₃ and O‐atom reactions with the target alcohols were confirmed to have a negligible contribution to their total losses by using two kinds of light sources with different relative rates of CH₃ONO and NO₂ photolysis. The absolute rate coefficients were obtained as the weighted mean values for the two reference compound systems and were k₁ = (6.6 ± 0.5) × 10^?11, k₂ = (9.7 ± 0.7) × 10^?11, and k₃ = (1.5 ± 0.1) × 10^?10 cm³ molecule^?1 s^?1 at 298 ± 2 K and 760 torr of air. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 379–385 2004     

Rate constants for the gas-phase reactions of Cl atoms with a series of hydrofluorocarbons and hydrochlorofluorocarbons at 298 ± 2 K

A relative rate method has been used to determine rate constants for the gas-phase reactions of a series of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) at 298 ± 2 K and atmospheric pressure of air. Based on a rate constant for the reaction of the Cl atom with CH₄ of (1.0 ± 0.2) ? 10^?13 cm³ molecule^?1 s^?1 at 298 K, the following Cl atom reaction rate constants (in units of 10^?15 cm³ molecule^?1 s^?1) were obtained: CH₃F, 340 ± 70; CH₃CHF₂, 240 ± 50; CH₂FCl, 110 ± 25; CHFCl₂, 21 ± 4; CHCl₂CF₃, 14 ± 3; CHFClCF₃, 2.7 ± 0.6; CH₃CFCl₂, 2.4 ± 0.5; CHF₂Cl, 2.0 ± 0.4; CH₂FCF₃, 1.6 ± 0.3; CH₃CF₂Cl, 0.37 ± 0.08; and CHF₂CF₃, 0.24 ± 0.05. These Cl atom reaction rate constants are compared with literature data and with the corresponding OH radical reaction rate constants. © John Wiley & Sons, Inc.     

Variational transition‐state theory study of the rate constant of the DMS·OH scavenging reaction by O2

The chemical tropospheric dimethyl sulfide (DMS, CH₃SCH₃) degradation involves several steps highly dependent on the environmental conditions. So, intensive efforts have been devoted during the last years to enhance the understanding of the DMS oxidation mechanism under different conditions. The reaction of DMS with OH is considered to be the most relevant process that initiates the whole oxidation process. The experimental observations have been explained by a two‐channel mechanism consisting of a H‐abstraction process leading to CH₃S(O)CH₃ and HO₂ and an addition reaction leading to the DMS · OH adduct. In the presence of O₂, the DMS · OH adduct is competitively scavenged increasing the contribution of the addition channel to the overall DMS oxidation. Recent experimental measurements have determined from a global fit that the rate constant of this scavenging process is independent of pressure and temperature but this rate constant cannot be directly measured. In this article, a variational transition‐state theory calculation of the low‐ and high‐pressure rate constants for the reaction between DMS · OH and O₂ has been carried out as a function of temperature. Our proposal is that the slight temperature dependence of the scavenging rate constant can only be explained if the H‐abstraction bottleneck is preceded by a dynamical bottleneck corresponding to the association process between the DMS · OH adduct and the O₂ molecule. The agreement between the low‐pressure and high‐pressure rate constants confirms the experimental observations. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Kinetics and mechanism of atmospheric reactions of partially fluorinated alcohols

Gas-phase reactions typical of the Earth’s atmosphere have been studied for a number of partially fluorinated alcohols (PFAs). The rate constants of the reactions of CF₃CH₂OH, CH₂FCH₂OH, and CHF₂CH₂OH with fluorine atoms have been determined by the relative measurement method. The rate constant for CF₃CH₂OH has been measured in the temperature range 258–358 K (k = (3.4 ± 2.0) × 10¹³exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(1.5 ± 1.3) kJ/mol). The rate constants for CH₂FCH₂OH and CHF₂CH₂OH have been determined at room temperature to be (8.3 ± 2.9) × 10¹³ (T = 295 K) and (6.4 ± 0.6) × 10¹³ (T = 296 K) cm³ mol^?1 s^?1, respectively. The rate constants of the reactions between dioxygen and primary radicals resulting from PFA + F reactions have been determined by the relative measurement method. The reaction between O₂ and the radicals of the general formula C₂H₂F₃O (CF₃CH₂? and CF₃?HOH) have been investigated in the temperature range 258–358 K to obtain k = (3.8 ± 2.0) × 10⁸exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(10.2 ± 1.5) kJ/mol. For the reaction between O₂ and the radicals of the general formula C₂H₄FO (? HFCH₂O, CH₂F?HOH, and CH₂FCH₂?) at T = 258–358 K, k = (1.3 ± 0.6) × 10¹¹exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(5.3 ± 1.4) kJ/mol. The rate constant of the reaction between O₂ and the radicals with the general formula C₂H₃F₂O (?F₂CH₂O, CHF₂?HOH, and CHF₂CH₂?) at T = 300 K is k = 1.32 × 10¹¹ cm³ mol^?1 s^?1. For the reaction between NO and the primary radicals with the general formula C₂H₂F₃O (CF₃CH₂? and CF₃?HOH), which result from the reaction CF₃CH₂OH + F, the rate constant at 298 K is k = 9.7 × 10⁹ cm³ mol^?1 s^?1. The experiments were carried out in a flow reactor, and the reaction mixture was analyzed mass-spectrometrically. A mechanism based on the results of our studies and on the literature data has been suggested for the atmospheric degradation of PFAs.     

Kinetics of the gas-phase reactions of the OH radical with (C2H5)3PO and (CH3O)2P(S)Cl at 296 ± 2 K

The kinetics of the gas-phase reactions of the OH radical with (C₂H₅O)₃PO and (CH₃O)₂P(S)Cl and of the reactions of NO₃ radicals and O₃ with (CH₃O)₂P(S)Cl have been studied at room temperature. Using a relative rate technique, the rate constants determined for the reactions of the OH radical with (C₂H₅O)₃PO and (CH₃O)₂P(S)Cl at 296 ± 2 K and 740 torr total pressure of air were (5.53 ± 0.35) × 10^?11 and (5.96 ± 0.38) × 10^?11 cm³ molecule^?1 s^?1, respectively. Upper limits to the rate constants for the NO₃ radical and O₃ reactions with (CH₃O)₂P(S)Cl of <3 × 10^?14 cm³ molecule^?1 s^?1 and <2 × 10^?19 cm³ molecule^?1 s^?1, respectively, were obtained. These data are compared and discussed with previous literature data for organophosphorus compounds.     

Kinetics and mechanism for the atmospheric oxidation of 1,1,2-trifluoroethane (HFC 143)

The rate constant for the reaction of the hydroxyl radical with 1,2,2-trifuoroethane has been determined over the temperature range 278–323 K using a relative rate technique. The results provide a value of k(OH + CH₂FCHF₂) = 2.65 × 10^?12 exp(?1542 ± 500/T) cm³ molecule^?1 s^?1 based on k(OH + CH₃CCl₃) = 1.2 × 10^?12 exp(?1400 ± 200/T) cm³ molecule^?1 s^?1 for the rate constant of the reference reaction. The chlorine atom initiated photooxidation of CH₂CHF₂ was investigated from 255 to 330 K and as a function of O₂ pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. The major carbon-containing products were CHFO and CF₂O suggesting that the alkoxy radicals CH₂FCF₂O and CHF₂CHFO, formed in the reaction, react predominantly by carbon-carbon bond cleavage. The results indicate that formation of CHF₂CFO from the reaction of CHF₂CHFO radicals with O₂ will be unimportant under all atmospheric conditions. © 1995 John Wiley & Sons, Inc.     

Rate constant and products of the reaction Cl + CS2 in air

A steady-state system involving the photolysis of Cl₂ as a source of Cl has been used to investigate the reaction of Cl with CS₂ at 293 ± 3 K in a 420 l reaction chamber coupled to FTIR and mass spectrometers. Using a relative rate technique, the measured effective rate constant was found to be dependent on the total pressure and mole fraction of O₂ present in the system. In 760 Torr synthetic air, the overall rate constant for the Cl + CS₂ reaction is(0.83 ± 0.17) × 10⁻¹³ cm³ molecule⁻¹s⁻¹. SO₂, COS and COCl₂ are the main reaction products.     

Kinetics of the reactions of OH radicals with n-alkanes at 299 ± 2 K

Relative rate constants for the reaction of OH radicals with a series of n-alkanes have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10^?12 cm³ molecule^?1s^?1, the rate constants obtained are (X10¹² cm³ molecule^?1 s^?1): propane 1.22 ± 0.05, n-pentane 4.13 ± 0.08, n-heptane 7.30 ± 0.17, n-octane 9.01 ± 0.19, n-nonane 10.7 ± 0.4, and n-decane 11.4 ± 0.6. The data for propane, n-pentane, and n-octane are in good agreement with literature values, while those for n-heptane, n-nonane, and n-decane are reported for the first time. These data show that the rate constant per secondary C—H bond is ∽40% higher for —CH₂— groups bonded to two other —CH₂— groups than for those bonded to a —CH₂— group and a —CH₃ group.     

OCS formation in the reaction of OH with CS2

A steady-state system involving photolysis of HONO as a source of OH was used to investigate the reaction of OH with CS₂ at 1 atm and 295 K. In the presence of O₂ ( > 40 Torr) a rapid reaction of OH with CS₂ occurs giving OCS. At lower O₂ concentrations, OCS formation ceases. In air the overall rate constant for OH + CS₂ → OCS was (1.7 ± 0.9) × 10^?12 cm³ molecule^?1 s^?1.     

Kinetics and products of the gas-phase reactions of the OH radical and O3 with allyl chloride and benzyl chloride at room temperature

The kinetics of the gas-phase reactions of allyl chloride and benzyl chloride with the OH radical and O₃ were investigated at 298 ± 2 K and atmospheric pressure. Direct measurements of the rate constants for reactions with ozone yielded values of ??(O₃ + allyl chloride) = (1.60 ± 0.18) × 10^?18 cm³ molecule^?1 s^?1 and ??(O₃ + benzyl chloride) < 6 × 10^?20 cm³ molecule^?1 s^?1. With the use of a relative rate technique and ethane as a scavenger of chlorine atoms produced in the OH radical reactions, rate constants of ??(OH + allyl chloride) = (1.69 ± 0.07) × 10^?11 cm³ molecule^?1 s^?1 and ??(OH + benzyl chloride) = (2.80 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1 were measured. A study of the OH radical reaction with allyl chloride by long pathlength FT-IR absorption spectroscopy indicated that the co-products ClCH₂CHO and HCHO account for ca. 44% of the reaction, and along with the other products HOCH₂CHO, (ClCH₂)₂CO, and CH₂ ? CHCHO account for 84 ± 16% of the allyl chloride reacting. The data indicate that in one atmosphere of air in the presence of NO the chloroalkoxy radical formed following OH radical addition to the terminal carbon atom of the double bond decomposes to yield HOCH₂CHO and the CH₂Cl radical, which becomes a significant source of the Cl atoms involved in secondary reactions. A product study of the OH radical reaction with benzyl chloride identified only benzaldehyde and peroxybenzoyl nitrate in low yields (ca. 8% and ?4%, respectively), with the remainder of the products being unidentified.