Spectrokinetic study of SF5 and SF5O2 radicals and the reaction of SF5O2 with NO

UV spectra of SF₅ and SF₅O₂ radicals in the gas phase at 295 K have been quantified using a pulse radiolysis UV absorption technique. The absorption spectrum of SF₅ was quantified from 220 to 240 nm. The absorption cross section at 220 nm was (5.5 ± 1.7) × 10⁻¹⁹ cm². When SF₅ was produced in the presence of O₂ an equilibrium between SF₅, O₂, and SF₅O₂ was established. The rate constant for the reaction of SF₅ radicals with O₂ was (8 ± 2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The decomposition rate constant for SF₅O₂ was (1.0 ± 0.5) × 10⁵ s⁻¹, giving an equilibrium constant of K_eq = [SF₅O₂]/[SF₅][O₂] = (8.0 ± 4.5) × 10⁻¹⁸ cm³ molecule⁻¹. The SF₅ O₂ bond strength is (13.7 ± 2.0) kcal mol⁻¹. The SF₅O₂ spectrum was broad with no fine structure and similar to the UV spectra of alkyl peroxy radicals. The absorption cross section at 230 nm was found to (3.7 ± 0.9) × 10⁻¹⁸ cm². The rate constant of the reaction of SF₅O₂ with NO was measured to (1.1 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ by monitoring the kinetics of NO₂ formation at 400 nm. The rate constant for the reaction of F atoms with SF₄ was measured by two relative methods to be (1.3 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. © 1994 John Wiley & Sons, Inc.     

Rate coefficients for CS reactions with O2, O3 and NO2 AT 298 K

CS radicals have been produced by photodissociation of CS₂ at 193 nm and their disappearance monitored by LIF. The vibrationally excited CS radicals rapidly relax to CS(ν = 0). At 298 K, the rate coefficients for CS(ν = 0) reactions with O₂, O₃ and NO₂ are (2.9 ± 0.4) × 10_?19, (3.0 ± 0.4) × 10^?16 and (7.6 ± 1.1) × 10^?17 cm³ molecule^?1 s^?1 respectively. The quenching of CS(A ¹II)_ν=0 by He has a rate coefficient of (1.3 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1.     

Photocurrent kinetics at the electron emission from a metal into electrolyte solution: Part II. Solutions without acceptors and solutions of N2O,NO2−, NO3−

A method of measuring the kinetics of currents arising at the electron photoemission from a metal into electrolyte solution when affected by the u.v. laser pulses for 10^?8 s at the frequency of repetitions 10–25 Hz is described. Measurements have been taken in solutions without acceptors and in those containing N₂O and NO₂^?, NO₃^? ions as electron acceptors. The rate constants of capture of the solvated electrons by N₂O ((6±1)×0⁹ mol^?1 s^?1) and NO₂^? ((4.5±1)×10⁹ mol^?1 s^?1) and the diffusion coefficients of OH-radicals ((1.0±0.3)×10^?5 cm² s^?1) and of NO ((1.2±0.3)×10^?5 cm² s^?1) are found. The oxidation rate of NO₃^2? has been shown to decrease from 40 cm s^?1 in the range of potentials ?0.55 to ?1.0 V. The rate constant of bimolecular recombination of the solvated electrons ((1.3±0.4)×10¹⁰ mol^?1 s^?1) has been found from the dependence of the emitted charge on the light intensity.     

Gas‐phase ozonolysis: Rate coefficients for a series of terpenes and rate coefficients and OH yields for 2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene

The kinetics of the gas‐phase reactions of O₃ with a series of selected terpenes has been investigated under flow‐tube conditions at a pressure of 100 mbar synthetic air at 295 ± 0.5 K. In the presence of a large excess of m‐xylene as an OH radical scavenger, rate coefficients k(O₃+terpene) were obtained with a relative rate technique, (unit: cm³ molecule^?1 s^?1, errors represent 2σ): α‐pinene: (1.1 ± 0.2) × 10^?16, ³Δ‐carene: (5.9 ± 1.0) × 10^?17, limonene: (2.5 ± 0.3) × 10^?16, myrcene: (4.8 ± 0.6) × 10^?16, trans‐ocimene: (5.5 ± 0.8) × 10^?16, terpinolene: (1.6 ± 0.4) × 10^?15 and α‐terpinene: (1.5 ± 0.4) × 10^?14. Absolute rate coefficients for the reaction of O₃ with the used reference substances (2‐methyl‐2‐butene and 2,3‐dimethyl‐2‐butene) were measured in a stopped‐flow system at a pressure of 500 mbar synthetic air at 295 ± 2 K using FT‐IR spectroscopy, (unit: cm³ molecule^?1 s^?1, errors represent 2σ ): 2‐methyl‐2‐butene: (4.1 ± 0.5) × 10^?16 and 2,3‐dimethyl‐2‐butene: (1.0 ± 0.2) × 10^?15. In addition, OH radical yields were found to be 0.47 ± 0.04 for 2‐methyl‐2‐butene and 0.77 ± 0.04 for 2,3‐dimethyl‐2‐butene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 394–403, 2002     

An FTIR study of the Cl-atom-initiated reaction of glyoxal

The kinetics and mechanism of Cl-atom-initiated reactions of CHO? CHO were studied using the FTIR detection method to monitor the photolysis of Cl₂–CHO? CHO mixtures in 700 torr of N₂–O₂ diluent at 298 ± 2 K. The observed product distribution in the [O₂] pressure of 0–700 torr combined with relative rate measurements provide evidence that: (1) the primary step is Cl + CHO? CHO → HCl + CHO? CO with a rate constant of [3.8 ± 0.3(σ)] × 10^?11 cm³ molecule^?1 s^?1; (2) the primary product CHO? CO unimolecularly dissociates to CHO and CO with an estimated lifetime of ≤ca. 1 × 10^?7 s; (3) alternatively, the CHO? CO reacts with O₂ leading to the formation of CO, CO₂, and most likely the HO radical, but no stable products containing two carbon atoms; (4) the HO₂ radical, formed in the secondary reaction CHO + O₂ → HO₂ + CO, reacts with the CHO? CHO with a rate constant ca. 5 × 10^?16 cm³ molecule^?1 s^?1 to form HCOOH and a new transient product resembling that detected previously in the HO₂ reaction with HCHO.     

Kinetic study of reactions of C2H5O2 with NO at 298 K and 0.55 – 2 torr

The kinetics of C₂H₅O₂ and C₂H₅O₂ radicals with NO have been studied at 298 K using the discharge flow technique coupled to laser induced fluorescence (LIF) and mass spectrometry analysis. The temporal profiles of C₂H₅O were monitored by LIF. The rate constant for C₂H₅O + NO → Products (2), measured in the presence of helium, has been found to be pressure dependent: k₂ = (1.25±0.04) × 10^?11, (1.66±0.06) × 10^?11, (1.81±0.06) × 10^?11 at P (He) = 0.55, 1 and 2 torr, respectively (units are cm³ molecule^?1 s^?1). The Lindemann-Hinshelwood analysis of these rate constant data and previous high pressure measurements indicates competition between association and disproportionation channels: C₂H₅O + NO + M → C₂H₅ONO + M (2a), C₂H₅O + NO → CH₃CHO + HNO (2b). The following calculated average values were obtained for the low and high pressure limits of k_2a and for k_2b : k = (2.6±1.0) × 10^?28 cm⁶ molecule^?2 s^?1, k = (3.1±0.8) × 10^?11 cm³ molecule^?1 s^?1 and k_2b ca. 8 × 10^?12 cm³ molecule^?1 s^?1. The present value of k, obtained with He as the third body, is significantly lower than the value (2.0±1.0) × 10^?27 cm⁶ molecule^?2 s^?1 recommended in air. The rate constant for the reaction C₂H₅O₂ + NO → C₂H₅O + NO₂ (3) has been measured at 1 torr of He from the simulation of experimental C₂H₅O profiles. The value obtained for k₃ = (8.2±1.6) × 10^?12 cm³ molecule^?1 s^?1 is in good agreement with previous studies using complementary methods. © 1995 John Wiley & Sons, Inc.     

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.     

Ion-Molecule reactions in methylamine and dimethylamine and trimethylamine systems

Fourier transform ion cyclotron resonance mass spectrometry has been used to measure the reaction rates for ions derived from methylamine with dimethylamine or trimethylamine. The use of the selective ion ejection technique greatly simplifies the elucidation of the ion-molecule reaction channels. The rate constants for proton transfer from protonated metwlamine, CH₃NH ₃ ⁺ (m/z 32), to dimethylamine and trimethylamine are 16.1 ± 1.6 × 10^?10 and 9.3 ± 0.9 × 10^?10 cm³ molec^?1s^?1, respectively. The rate constants for charge transfer from methylamine molecular ion, CH₃NH ₂ ⁺ (m/z 31), to dimethylamine and trimethylamine are 9.3 ± 1.8 x 10^?10 and 15.0 ± 5 × 10^?10 cm³molec^?1s^?1, respectively.     

Rate Coefficients of the Reactions of CN and NCO with O2 and NO2 at 296 K

The rate coefficients of the reactions of CN and NCO radicals with O₂ and NO₂ at 296 K: (1) CN + O₂ → products; (2) CN + NO₂ → products; (3) NCO + O₂ → products and (4) NCO + NO₂ → products have been measured with the laser photolysis-laser induced fluorescence technique. We obtained k₁ = (2.1 ± 0.3) × 10^?11 and k₂ = (7.2 ± 1.0) × 10^?11 cm³ molecule^?t s^?1 which agree well with published results. As no reaction was observed between NCO and O₂ at 297 K, an upper limit of k₃ < 4 × 10^?17 cm³ molecule^?1 S^?1 was estimated. The reaction of NCO with NO₂ has not been investigated previously. We measured k₄ = (2.2 ± 0.3) × 10^?11 cm³ molecule^?1 s^?1 at 296 K.     

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.     

Proton transfer reactions from H3+ ions to N2, O2, and CO molecules

The rate constants for proton transfer from H₃⁺ ions to N₂, O₂, and CO have been measured as function of hydrogen buffer gas partial pressure. The rate constant for proton transfer from H₃⁺ to N₂ shows a very large pressure dependence, increasing from 1.0 × 10^?9 cm³/s at low H₂ partial pressures to 1.7 × 10^?9 cm³/s at high H₂ partial pressures. The rate constants for proton transfer from H₃⁺ to O₂ and CO are constant with partial pressure of H₂; giving values of 6.4 × 10^?10 cm³/s and 1.7 × 10^?9 cm³/s, respectively. The roles of excess vibrational energy in H₃⁺ ions and of equilibrium between forward and back reaction are discussed. Back reaction is observed only for the reaction of H₃⁺ ions with O₂, and an equilibrium constant of K = 2.0 ± 0.4 at 298 K has been determined. From these data the proton affinity of O₂ is deduced to be 0.47 ± 0.11 kcal/mole higher than that of H₂.     

UV absorption spectrum of CF3CFClO2 and kinetics of the self reaction of CF3CFCl and CF3CFClO2 and the reactions of CF3CFClO2 with NO and NO2

The ultraviolet absorption spectrum of CF₃CFClO₂ and the kinetics of the self reactions of CF₃CFCl and CF₃CFClO₂ radicals and the reactions of CF₃CFClO₂ with NO and NO₂ have been studied in the gas phase at 295 K by pulse radiolysis/transient UV absorption spectroscopy. The UV absorption cross section of CF₃CFCl radicals was measured to be (1.78 ± 0.22) × 10^?18 cm² molecule^?1 at 220 nm. The UV spectrum of CF₃CFClO₂ radicals was quantified from 220 nm to 290 nm. The absorption cross section at 250 nm was determined to be (1.67 ± 0.21) × 10^?18 cm² molecule^?1. The rate constants for the self reactions of CF₃CFCl and CF₃CFClO₂ radicals were (2.6 ± 0.4) × 10^?12 cm³ molecule^?1 s^?1 and (2.6 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1, respectively. The reactivity of CF₃CFClO₂ radicals towards NO and NO₂ was determined to (1.5 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 and (5.9 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1, respectively. Finally, the rate constant for the reaction of F atoms with CF₃CFClH was determined to (8 ± 2) × 10^?13 cm³ molecule^?1 s^?1. Results are discussed in the context of the atmospheric chemistry of HCFC-124, CF₃CFClH. © 1994 John Wiley & Sons, Inc.     

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.     

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 of the reaction of atomic fluorine with phosphorous trifluoride: ESR determination

The reaction rate constant of the addition of atomic fluorine to excess PF₃ was determined by fast flow ESR measurements to be (8.6 ± 0.6) × 10¹² cm³ mole^?1 s^?1 at 300 K. The stoichiometry of the overall reaction of F with PF₃ was 2:1. Finite difference calculations simulating several reaction mechanisms suggest that the reaction occurs in two consecutive addition steps, F + PF₃ = PF₄ and F + PF₄ = PF₅. Assuming this mechanism is correct, the rate constant for the second reaction would be approximately (1.2 ± 0.2) × 10¹³ cm³ mole^?1 s^?1.     

Kinetic study of the reaction of chlorine atoms with CF3I and the reactions of CF3 radicals with O2, Cl2 and NO at 296 K

The kinetics of the gas-phase reaction of Cl atoms with CF₃I have been studied relative to the reaction of Cl atoms with CH₄ over the temperature range 271–363 K. Using k(Cl + CH₄) = 9.6 × 10^?12 exp(?2680/RT) cm³ molecule^?1 s^?1, we derive k(Cl + CF₃I) = 6.25 × 10^?11 exp(?2970/RT) in which E_a has units of cal mol^?1. CF₃ radicals are produced from the reaction of Cl with CF₃I in a yield which was indistinguishable from 100%. Other relative rate constant ratios measured at 296 K during these experiments were k(Cl + C₂F₅I)/k(Cl + CF₃I) = 11.0 ± 0.6 and k(Cl + C₂F₅I)/k(Cl + C₂H₅Cl) = 0.49 ± 0.02. The reaction of CF₃ radicals with Cl₂ was studied relative to that with O₂ at pressures from 4 to 700 torr of N₂ diluent. By using the published absolute rate constants for k(CF₃ + O₂) at 1–10 torr to calibrate the pressure dependence of these relative rate constants, values of the low- and high-pressure limiting rate constants have been determined at 296 K using a Troe expression: k₀(CF₃ + O₂) = (4.8 ± 1.2) × 10^?29 cm⁶ molecule^?2 s^?1; k_∞(CF₃ + O₂) = (3.95 ± 0.25) × 10^?12 cm³ molecule^?1 s^?1; F_c = 0.46. The value of the rate constant k(CF₃ + Cl₂) was determined to be (3.5 ± 0.4) × 10^?14 cm³ molecule^?1 s^?1 at 296 K. The reaction of Cl atoms with CF₃I is a convenient way to prepare CF₃ radicals for laboratory study. © 1995 John Wiley & Sons, Inc.     

Flash photolysis resonance fluorescence study of the reaction Cl + O3 → ClO + O2 over the temperature range 213–298 K

Rate constants for the removal of Cl atoms in the reaction Cl + O₃ → ClO + O₂ were measured by the flash photolysis resonance fluorescence technique over the temperature range 213–298 K. The rate constant is given by the Arrhenius expression (2.94 ± 0.49) × 10^?11 exp[?(298 ± 39)/T] in units of cm³ molecule^?1 s^?1. Comparison with recent results from other laboratories are presented.     

Time-resolved investigation of the de-excitation of xenon excimer by SF6 and N2 excited with synchrotron radiation

An attempt has been made 'o measure the rate constant for the de-excitation of a state-specified excimer using the pulse character of synchrotron radiation. The rate constants have been obtained for de-excitation of a vibrationally relaxed excimer Xe₂^*(O_u⁺; low v) by SF₆ and N₂ as 9 × 10^?10 and 7 × 10^?12 cm³ molecule^?1 s^?1 respectively.     

Singlet exciton interactions in crystalline naphthalene

The decay of prompt fluorescence in crystalline naphthalene at 300 K, excited by a picosecond 266 nm pulse, has been studied as a function of excitation intensity. Experimental decay curves can be fitted only when the exponential distribution in depth of excitation and the radial (gaussian) intensity profile of the excitation are both taken into account. From an analysis of the decay at early time (?5 ns) a best fit value of the singlet—singlet annihilation rate constant is found γ_SS = (4 ± 1) × 10^?10 cm³ s^?1. If the reaction is diffusion-limited, this rate implies an average singlet diffusivity D_S = (2 ± 1) × 10^?4 cm² s^?1.     

A spectrokinetic study of CH2I and CH2IO2 radicals

The UV absorption spectrum and kinetics of CH₂I and CH₂IO₂ radicals have been studied in the gasphase at 295 K using a pulse radiolysis UV absorption spectroscopic technique. UV absorption spectra of CH₂I and CH₂IO₂ radicals were quantified in the range 220–400 nm. The spectrum of CH₂I has absorption maxima at 280 nm and 337.5 nm. The absorption cross-section for the CH₂I radicals at 337.5 nm was (4.1 ± 0.9) × 10^?18 cm² molecule^?1. The UV spectrum of CH₂IO₂ radicals is broad. The absorption cross-section at 370 nm was (2.1 ± 0.5) × 10^?18 cm² molecule^?1. The rate constant for the self reaction of CH₂I radicals, k = 4 × 10^?11 cm³ molecule^?1 s^?1 at 1000 mbar total pressure of SF₆, was derived by kinetic modelling of experimental absorbance transients. The observed self-reaction rate constant for CH₂IO₂ radicals was estimated also by modelling to k = 9 × 10^?11 cm³ molecule^?1 s^?1. As part of this work a rate constant of (2.0 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1 was measured for the reaction of F atoms with CH₃I. The branching ratios of this reaction for abstraction of an I atom and a H atom were determined to (64 ± 6)% and (36 ± 6)%, respectively. © 1994 John Wiley & Sons, Inc.