Rate constants for the reaction of ground-state oxygen atoms with methanol from 297 to 544 K

The rate constant for the reaction of ground-state oxygen atoms with methanol has been determined between 297 and 544 K by a phase-shift technique using mercury photosensitized decomposition of N₂O to generate oxygen atoms. The relative oxygen atom concentration was monitored by the chemiluminescence from the reaction of oxygen atoms with nitric oxide. The results are accommodated by the Arrhenius expression k₁ = (9.79 ± 2.71) × 10¹² exp[(?2267 ± 111)/T]cm³/mol·s, where the indicated uncertainties are 95% confidence limits for 10 degrees of freedom. As an incidental part of this work, the third-body efficiency of CH₃OH relative to N₂O for the reaction O + NO + M → NO₂ + M (M = CH₃OH) was determined to be 3.1 at 298 K.     

Rate constants for the reaction of singlet oxygen with diazocompounds

Rate constants for the reaction of singlet oxygen with a series of diazocompounds and diazoketones have been measured. Diazoketones were found to possess lower reactivity than diazocompounds.

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Rate of reaction of dimethylmercury with oxygen atoms in the gas phase

The rate constant for the reaction of atomic oxygen (O(³P)) with dimethylmercury has been measured at room temperature at a pressure of about 1 Torr using a fast flow system with electron paramagnetic resonance and mass spectrometric detection. Some reaction products were identified. The rate constant found is (2.5 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹.     

Ab initio study on mechanisms of singlet oxygen reaction with ethylene

The reaction of singlet oxygen with ethylene has been studied at the ab initio level with both HF/3-21G and HF/6-31G basis sets, fully optimizing the geometries of the critical points. The transition state leading to the intermediate peroxirane from the initial reactants is found,Iocated at 81.71 kJ/mol above the dissociation limit. The vibrational analysis is done with two basis sets. From the results it can be seen that the frequencies have not been made an improvement obviously with augmented 6-31G compared to 3-21G basis; it follows that main reason for too high HF/3-21G frequency could mainly be the vibrational anharmonicity. The eigenvector corresponding to the single imaginary vibrational frequency is dominated by the larger O-O distance. The finding of the transition state confirms that the peroxirane minimum can be reachable passing through a peroxirane-like saddle point. In addition , the mechanisms of the reaction forming oxirane are discussed as well.     

Measurement of the reaction rate constants of oxygen atoms with chlorine and iodomethane using a resonance fluorescence technique

The following reaction rate constants of oxygen atoms with iodomethane and chlorine were measured using resonance fluorescence under jet conditions at 298 K: k ₁ = (2.4 ± 0.5) × 10–15 and k ₂ = (6.9 ± 0.2) × 10⁻¹⁴ cm³/s, respectively.     

Rate constants of the reaction between alkyl radicals and oxygen and stable nitroxyl radicals

Conclusions The rate constants of the reaction between the alkyl radicals of hydrocarbons (R^.) and of vinyl monomers (M^.) and O₂ and stable nitroxyl radicals were determined at 50C. The low-molecular-weight radicals react with O₂ (k₁) and the (k₃) more rapidly than the M^. do. For polar R^. and M^. k₁ and k₃ are close, and for the nonpolar ones k₁>k₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2446–2450, November, 1979.The authors express their appreciation to V. A. Golubev for submitting the nitroxyl radicals and A. P. Moravskii for help in running the experiment.     

Rate constants for the reaction of Cl atoms with O3 at temperatures from 298 to 184 K

Using the standard, low pressure, discharge‐flow technique, with resonance fluorescence in the vacuum ultraviolet to observe Cl atoms, rate constants have been determined for the reaction of Cl atoms with O₃ at temperatures down to 184 K. The measured rate constants for 298–184 K fit the Arrhenius expression k(T) = (3.1 ± 1.3₅) × 10^?11 exp((?280 ±100 K)/T) cm³ molecule^?1 s^?1. The results extend the data on this key atmospheric reaction to slightly lower temperatures. The data are in fairly good agreement with those currently in the literature but suggest that the rate constant is approximately 15% lower than that given by currently recommended rate expressions at the lowest temperatures found in the stratosphere.© 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 104–109, 2002     

Formation of oxygen atoms in the reaction of chlorine atoms with ozone

Oxygen atoms are detected by NO + O + M chemiluminescence as a secondary product of the reaction between Cl and O₃. The mechanism Cl + O₃ → ClO + O₂(¹Σ⁺_g), O₂(¹Σ⁺_g) + O₃ → O₂ + O₂ + O is proposed to account for the oxygen atom formation. The branching ratio to the O₂(¹Σ⁺_g) product in the reaction of Cl with O₃ is estimated to be in the range (0.1–0.5) x 10^?2.     

Radiation-induced terpolymerization of tetrafluoroethylene with propylene and isobutylene in bulk

Terpolymerization of tetrafluoroethylene (TFE) with propylene (P) and isobutylene (iB) by γ radiation at temperatures of ?78 to 40°C, a dose rate of 5 × 10⁴?5 × 10⁵ rad/hr, and an iB/P molar ratio of 40/10?5/45 in the monomer mixture was carried out. Alternating copolymers of TFE and α-olefins, that is, P and iB, were formed at various monomer compositions. No crystalline structure was observed in the terpolymer obtained below an iB/P molar ratio of 15/35 in the monomer mixture but a partly crystalline order increased with the amounts of iB in terpolymer. The crystal lattice of the TFE–iB copolymer was affected by the introduction of P. The dose rate dependencies of the polymerization rate and inherent viscosity were 0.8 and ?0.2, respectively. The activation energy of polymerization was 2.4 kcal/mole, and the relative reactivity ratio of iB and P for a TFE radical chain end was estimated as 4.50 by the treatment of the free propagating mechanism.     

Abstraction by hydrogen atoms from ethylene,propylene, butene-1, and cis- and trans-butene-2

The position of abstraction by H atoms from ethylene, propylene, butene-1, and cis- and trans-butene-2 and the rates of abstraction relative to addition have been measured at 25°C. Only allylic abstraction was observed. From ethylene, abstraction relative to addition was ≤3×10^?4. For propylene, butene-1, cis-butene-2, and trans-butene-2, abstraction occurred on 0.2%, 1.6%, 1.5%, and 0.9% of the reactive encounters, if dis-proprotionation-combination ratios for allyl and alkyl radicals are similar to those for alkyl–alkyl pairs.     

Rate constants for the reactions of Cl atoms with HCOOH and with HOCO radicals

Rate constants have been measured at room temperature for the reactions of Cl atoms with formic acid and with the HOCO radical: Cl + HCOOH → HCl + HOCO (R1) Cl + HOCO → HCl + CO₂ (R2) Cl atoms were generated by flash photolysis of Cl₂ and the progress of reaction was followed by time‐resolved infrared absorption measurements using tunable diode lasers on the CO₂ that was formed either in the pair of reactions ( R1 ) plus ( R2 ), or in reaction ( R1 ) followed by O₂ + HOCO → HO₂ + CO₂ (R3) In a separate series of experiments, conditions were chosen so that the kinetics of CO₂ formation were dominated either by the rate of reaction ( R1 ) or by that of reactions ( R1 ) and ( R2 ) combined. The results of our analysis of these experiments yielded: k₁ = (1.8₃ ± 0.12) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ k₂ = (4.8 ± 1.0) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 85–91, 2000     

Rate constants for reactions of iodine atoms in solution

Laser flash photolysis (at 248 or 308 nm) or aryl iodides in water or water/methanol solutions produces iodine atoms and phenyl radicals. Iodine atoms react rapidly with added I^? to form I₂^? but do not react rapidly with O₂ (k ? 10⁷ L mol^?1 s^?1). Iodine atoms oxidize phenols to phenoxyl radicals, with rate constants that vary from 1.6 × 10⁷ L mol^?1 s^?1 for phenol to about 6 × 10⁹ L mol^?1 s^?1 for 4-methoxyphenol and hydroquinone. Ascorbate and a Vitamin E analogue are also oxidized very rapidly. N-Methylindole is oxidized by I atoms to its radical cation with a diffusion-controlled rate constant, 1.9 × 10¹⁰ L mol^?1 s^?1. Iodine atoms also oxidize sulfite and ferrocyanide ions rapidly but do not add to double bonds. The phenyl radicals, produced along with the I atoms, react with O₂ to give phenylperoxyl radicals, which react with phenols much more slowly than I atoms. © 1995 John Wiley & Sons, Inc.