Absolute Rate Constants For Reaction Research Articles

Electron attachment reactions of perfluoroalkyl transition metal carbonyls: Rate constants and product analysis

Absolute rate constants for electron attachment reactions of CF3Mn(CO)5, CF3Co(CO)4, and C2F5Co(CO)4 have been measured in a gas flow system with electron cyclotron resonance (ECR) detection. Free electrons were generated by Penning ionization of argon gas by helium metastables produced in a low power radio-frequency discharge. The pressure was 2.3–2.5 Torr. The rate constants at 293 K in units of cm3 molecule−1 s−1 are (3.5±0.6)×10−7 for CF3Mn(CO)5; (2.0±0.4)×10−7 for CF3Co(CO)4; and (1.8±0.3)×10−7 for C2F5Co(CO)4. Negative ion mass spectra indicate that nondissociative attachment is important at thermal electron energy. The cross section for nondissociative capture falls rapidly with increasing electron energy. Dissociative product channels are also observed. Electron capture rate constants for several additional molecules are presented and compared with values from the literature. The rate constants in units of cm3 molecule−1 s−1 are 2.8×10−7 for SF6; 3.7×10−7 for CCl4; 3.1×10−7 for CFCl3; 1.8×10−9 for CF2Cl2; 1.5×10−8 for CF3Br; 3.8×10−9 for CHCl3; and 1.2×10−8 for C2F3Cl3.

ESR Studies on Chain Transfer Reactions: Rate Constants for the Reactions of Model Radicals of Polystyrene Growing Chain Ends with Tetrahalomethanes and Thiophenols

Abstract The absolute rate constants for reactions of the model radicals of the growing chain ends of styrene and methacrylonitrile with tetrahalomethanes and thiophenols were determined by spin-trapping methods using ESR spectroscopy. The model radicals were produced by the photodecomposition of 1,1′-diphenylazoethane and 2,2′-azobisisobutyronitrile. In the case of the styrene model radical, the rate constants for the halogen abstraction reaction from CBr4, CBrCl3, and CCl4 were 1.1×107, 2.0×106, and 1.1×105 M−1s−1, respectively, and increased with increasing electron affinity of tetrahalomethanes. The rate constants for the hydrogen abstraction reaction from thiophenols were of the order 106 M−1s−1, independent of the electron-donating and -accepting properties of the para substituents. In the case of the methacrylonitrile model radical, the rate constants for the halogen abstraction reaction from CBr4 and CBrCl3 were 1.1×105 and 4.5×103 M−1s−1, respectively. The rate constants for the hydrogen abstraction reaction from thiophenols with –CH3, –H, and –Cl substituent in the para position were 4.5×104, 2.7×104, and 1.7×104 M−1s−1, respectively. The rate constants decreased with increasing the electron-withdrawing power of the substituent.

Unusual selectivities of radical reactions. Experimental studies on alkyl versus phenoxyl reaction systems

AbstractRadical reactions involving two or more intermediates and many mutual reaction channels may lead to the specific formation of one cross‐reaction product if one species is rather persistent and if transient and persistent species are produced with equal rates. A previous kinetic analysis of the phenomenon revealed that the concentrations of the intermediates and the selectivities of product formation depend critically on the relative initiation rates. The present experimental ESR studies on systems involving simultaneously generated phenoxyl radicals as persistent and alkyl radicals as transient species confirm the predicted behavior. They also lead to absolute rate constants for reactions of alkyl with phenoxyl radicals and for hydrogen atom transfer from phenols to alkyl radicals.

Substituent effects on the free-radical addition reactions of arylthiyl radicals with arylacetylenes

Absolute rate constants for addition reactions of arylthiyl radicals (YC6H4S˙) to arylacetylenes (XC6H4CCH) have been determined by a flash-photolysis method. The rate constants (in dm3 mol–1 s–1) vary from 1.0 × 105(X =m-NO2 and Y =p-MeO) to 1.0 × 107(X =p-MeO and Y =p-Br). For all arylthiyl radicals, a Hammett plot of the σ+-constants for the X-substituents yields negative ρ+(Y) values. The ρ+(Y) values depend also on the Y-substituents on the arylthiyl radicals [ρ+(Y)=–0.22 for Y =p-MeO and ρ+(Y)=–0.53 for Y =p-Br]. These ρ+(Y) values are slightly smaller than the ρ+(Y) values reported for the corresponding arenesulphonyl radicals, reflecting the low electrophilicity of the arylthiyl radicals. On the other hand, for each arylacetylene a Hammett plot of the rate constants for YC6H4S˙vs. σ+(Y) yields positive ρ+(X) values which increase with the increasing electron density on the triple bond.

ChemInform Abstract: 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.

Temperature dependence of the rate constants of the reactions of hydroxyl radicals with acetylene and acetylene-d2 at 1 atm in argon from 333 to 1273 K

The absolute rate constants for the gas-phase reactions of OH + C/sub 2/H/sub 2/ and OH + C/sub 2/D/sub 2/ were measured at a total pressure of 1 atm in argon buffer gas from 333 to 1273 K by using the pulse radiolysis technique. The predominant reactions were found to change from the addition reaction at lower temperatures to the H-atom abstraction reaction at higher temperatures. The kinetic isotope effect of k(H)/k(D) was /approximately/ 1 below 393 K, 1 above 1073 K. From the experimental data of this work and the previous investigations, the second-order constant for addition reaction could be expressed as 8.5 /times/ 10/sup /minus/12/e/sup (-1400/plus minus/60)/RT/ cm/sup 3/ molecule/sup /minus/1/ s/sup /minus/1/ and for H-atom abstraction reaction as 4.5 /times/ 10/sup /minus/11/e/sup (-10,500/plus minus/3100)/RT/ cm/sup 3/ molecule/sup /minus/1/ s/sup /minus/1/. The indicated error limit in the Arrhenius activation energy is 1 standard deviation of the least-squares analysis.

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

AbstractThe 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, &lt;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.

Absolute and relative rate constants for the gas-phase reaction of OH radicals with CH 3NO 2, CD 3NO 2 and CH 3CH 2CH 3 at 295 K and 1 ATM

The rate constants for the gas-phase reaction of OH radicals with nitromethane, deutero-nitromethane and propane have been determined at 295 ± 2 K and a total pressure of approximately 1 atm; a photolytic relative technique and an absolute method were applied. Methyl nitrite was used as the OH source in the relative method. In the absolute technique, pulse radiolysis was combined with kinetic spectroscopy. H 2O-Ar mixtures were irradiated and the OH kinetics recorded by following the transient light absorption around 309 nm. The results are compared with literature data.

Kinetics and spectroscopy of ylids from reaction of p-substituted phenylchlorocarbenes with acetone

Laser flash photolysis of p-CF 3 and p-Cl-phenylchloro diazirines produces the corresponding carbenes which react with acetone to produce easily detected ylids. The absolute rate constants of reaction of these carbenes with acetone, and the rate constants of reaction of the ylids with diethylfumarate have been determined. No reaction was found between these carbenes and simple esters or ethylene carbonate.

Absolute rate constants for silylene reactions with diatomic molecules

Absolute rate constants have been determined for the reaction of SiH 2 with the diatomics HCl, Cl 2, NO and O 2. Upper limits are reported for rate constants for the reaction of SiH 2 with N 2 and CO. Comparisons are made between the reactivity of silylene, singlet methylene and halogenated silylenes.

Chemistry of Isolated Transition Metal Clusters

Clusters containing two to several hundred atoms are generated by pulsed laser vaporization of a metal target located in a flow tube reactor. A continuous flow of inert carrier gas entrains and cools the vaporized plume of metal, resulting in rapid cluster growth. Reactant gases are injected into the flow downstream of the target, at a point where cluster growth has finished. After reagent mixing and chemical reactions occur, the products exit the tube into a vacuum, and are formed into a molecular beam by collimators located in successive stages of differential pumping. In the highest vacuum stage the reaction products are identified by pulsed laser ionization and time-of-flight mass spectrometry. Studies to be discussed include measurements of absolute reaction rate constants, hydrogen uptake experiments, laser-induced desorption of adsorbates from clusters, and cluster-catalyzed chemical reactions. Such work provides us with information about the dependence of reactivity on cluster size, the geometrical configuration of cluster binding sites, the thermodynamics of adsorbate bonding, and the mechanisms of chemical reactions of cluster surfaces. These studies are bringing us closer to a detailed understanding of the interactions of metal surfaces with atoms and simple molecules.

Absolute rate constants for silylene reactions with hydrocarbons at 298 K

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAbsolute rate constants for silylene reactions with hydrocarbons at 298 KJack O. Chu, David B. Beach, and Joseph M. JasinskiCite this: J. Phys. Chem. 1987, 91, 20, 5340–5343Publication Date (Print):September 1, 1987Publication History Published online1 May 2002Published inissue 1 September 1987https://doi.org/10.1021/j100304a040RIGHTS & PERMISSIONSArticle Views74Altmetric-Citations51LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (556 KB) Get e-Alerts

Absolute rate constants of alkoxyl radical reactions in aqueous solution

The pulse radiolysis technique was used to generate the alkoxyl radical derived from tert-butyl hydroperoxide (/sup t/BuOOH) in aqueous solution. The reactions of this radical with 2,2'-azinobis(3-ethyl-6-benzothiazolinesulfonate) (ABTS) and promethazine were monitored by kinetic spectroscopy. The unimolecular decay rate constant of the tert-butoxyl radical (/sup t/BuO) was determined to be 1.4 x 10/sup 6/ s/sup -1/. On the basis of this value, the rate constants for /sup t/BuO attack on quercetin, crocin, crocetin, ascorbate, isoascorbate, trolox c, glutathione, thymidine, adenosine, guanosine, and unsaturated fatty acids were determined. In addition, the reaction of /sup t/BuO with the polyunsaturated fatty acids (PUFA) was observed by directly monitoring the formation of the fatty acid pentadienyl radicals. Interestingly, the attack of /sup t/BuO on PUFA was found to be faster by about one order of magnitude as compared to the same reaction in a nonpolar solvent.

ChemInform Abstract: Absolute Rate Constants for the Gas‐Phase Reactions of the NO3 Radical with CH3SH, CH3SCH3, CH3SSCH3, H2S, SO2, and CH3OCH3 Over the Temperature Range 280‐350 K.

ChemInformVolume 18, Issue 8 Preparative Organic Chemistry ChemInform Abstract: Absolute Rate Constants for the Gas-Phase Reactions of the NO3 Radical with CH3SH, CH3SCH3, CH3SSCH3, H2S, SO2, and CH3OCH3 Over the Temperature Range 280-350 K. T. J. WALLINGTON, T. J. WALLINGTON Statewide Air Pollut. Res. Cent., Univ. Calif., Riverside, CA 92521, USASearch for more papers by this authorR. ATKINSON, R. ATKINSON Statewide Air Pollut. Res. Cent., Univ. Calif., Riverside, CA 92521, USASearch for more papers by this authorA. M. WINER, A. M. WINER Statewide Air Pollut. Res. Cent., Univ. Calif., Riverside, CA 92521, USASearch for more papers by this authorJ. N. JUN. PITTS, J. N. JUN. PITTS Statewide Air Pollut. Res. Cent., Univ. Calif., Riverside, CA 92521, USASearch for more papers by this author T. J. WALLINGTON, T. J. WALLINGTON Statewide Air Pollut. Res. Cent., Univ. Calif., Riverside, CA 92521, USASearch for more papers by this authorR. ATKINSON, R. ATKINSON Statewide Air Pollut. Res. Cent., Univ. Calif., Riverside, CA 92521, USASearch for more papers by this authorA. M. WINER, A. M. WINER Statewide Air Pollut. Res. Cent., Univ. Calif., Riverside, CA 92521, USASearch for more papers by this authorJ. N. JUN. PITTS, J. N. JUN. PITTS Statewide Air Pollut. Res. Cent., Univ. Calif., Riverside, CA 92521, USASearch for more papers by this author First published: February 24, 1987 https://doi.org/10.1002/chin.198708120AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue8February 24, 1987 RelatedInformation

Measurement of absolute rate data for the reaction of atomic potassium, K(42S1/2), with CF3Cl, CF2Cl2, CFCl3, CF3Br and SF6as a function of temperature by time-resolved atomic resonance absorption spectroscopy at λ= 404 nm [K(52PJ)â†� K(42S1/2)

We present a kinetic study of the reactions of atomic potassium in its electronic ground state, K(42S1/2), with the molecules CF3Cl, CF2Cl2, CFCl3, CF3Br and SF6. Atomic potassium was generated by pulsed irradiation of potassium halide vapour at elevated temperatures and monitored in the ‘single-shot mode’ by time-resolved atomic resonance absorption using the Rydberg doublet at λ= 404 nm [K(5 2PJ)â†� K(4 2S1/2)]. Absolute rate constants for reaction with these molecules were determined as a function of temperature yielding the following Arrhenius parameters (errors 1σ): [graphic omitted]. CF4 exhibited anomalous kinetic behaviour. These results represent the first kinetic measurements, relative or absolute, for these fundamental reactions of atomic potassium. This new set of absolute rate data are compared with analogous results reported hitherto for atomic sodium, Na(3 2S1/2), both alkali-metal atoms exhibiting rapid reactions characterised by small energy barriers and being highly exothermic in character.

ChemInform Abstract: Absolute Third‐order Rate Constants for the Recombination Reactions Between Alkali‐metal and Iodine Atoms and the Measurement for Rb + I + He.

Chemischer InformationsdienstVolume 17, Issue 41 Physical Inorganic Chemistry ChemInform Abstract: Absolute Third-order Rate Constants for the Recombination Reactions Between Alkali-metal and Iodine Atoms and the Measurement for Rb + I + He. J. M. C. PLANE, J. M. C. PLANESearch for more papers by this authorD. HUSAIN, D. HUSAINSearch for more papers by this author J. M. C. PLANE, J. M. C. PLANESearch for more papers by this authorD. HUSAIN, D. HUSAINSearch for more papers by this author First published: October 14, 1986 https://doi.org/10.1002/chin.198641023Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume17, Issue41October 14, 1986 RelatedInformation

Absolute rate constants for the gas-phase reactions of the nitrogen trioxide radical with methanethiol, dimethyl sulfide, dimethyl disulfide, hydrogen sulfide, sulfur dioxide, and dimethyl ether over the temperature range 280-350 K

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAbsolute rate constants for the gas-phase reactions of the nitrogen trioxide radical with methanethiol, dimethyl sulfide, dimethyl disulfide, hydrogen sulfide, sulfur dioxide, and dimethyl ether over the temperature range 280-350 KTimothy J. Wallington, Roger Atkinson, Arthur M. Winer, and James N. Pitts Jr.Cite this: J. Phys. Chem. 1986, 90, 21, 5393–5396Publication Date (Print):October 1, 1986Publication History Published online1 May 2002Published inissue 1 October 1986https://doi.org/10.1021/j100412a099RIGHTS & PERMISSIONSArticle Views105Altmetric-Citations55LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (493 KB) Get e-Alerts

Absolute rate constants for the gas-phase reaction of the nitrate radical with dimethyl sulfide, nitrogen dioxide, carbon monoxide and a series of alkanes at 298 .+-. 2 K

A flash photolysis-visible absorption apparatus has been constructed and employed in a study of the kinetics of the gas-phase reactions of the NO/sub 3/ radical with CH/sub 3/SCH/sub 3/, NO/sub 2/, CO, CH/sub 4/, C/sub 2/H/sub 6/, and n-C/sub 4/H/sub 10/. The measured absolute rate constants at 298 +/- 2 K are as follows (in units of 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/): CH/sub 3/SCH/sub 3/, 7.5 +/- 0.5 independent of pressure over the range 50-400 Torr; NO/sub 2/, 5.6 +/- 0.4 and 8.0 +/- 1.1 at 120 and 400 Torr total pressure of helium, respectively; CO, less than or equal to 0.00003; CH/sub 4/, less than or equal to 0.0002; C/sub 2/H/sub 6/, less than or equal to 0.00004; n-C/sub 4/H/sub 10/, less than or equal to 0.0002. The error limits represent two standard deviations. (Systematic errors could contribute an additional approx. 10% range.) These results are discussed with respect to the previous literature data and the atmospheric lifetimes of these compounds. The rate constant for the reaction of NO/sub 3/ radicals with CH/sub 3/SCH/sub 3/ measured in the present work is consistent with both another recent absolute determination and previous relative rate measurements, confirming the relativemore » rate technique previously used to determine NO/sub 3/ radical reaction rate constants.« less

ChemInform Abstract: Kinetics of the Gas Phase Reaction of OH Radicals with Pyrrole and Thiophene

Absolute rate constants for the gas phase reaction of OH radicals with pyrrole (k1) and thiophene (k2) have been measured over the temperature ranges 298–440 and 274–382 K, respectively, using the flash photolysis-resonance fluorescence technique. The rate constants obtained were independent of the total pressure of argon diluent over the range 25–100 torr andwere fit by the Arrhenius expressions and with rate constants at 298 ± 2 K of k1 = (1.03 ± 0.06) × 10−10 cm3 molecule−1 s−1 and k2 = (8.9 ± 0.7) × 10−12 cm3 molecule−1 s−1. [These errors represent two standard deviations (systematic errors could constitute an additional ca. 10% uncertainty)]. These results are discussed with respect to the previous literature data and the atmospheric lifetimes of pyrrole and thiophene.

Absolute rate constants for the gas-phase reaction of OH radicals with cyclohexane and ethane at 295 K

The absolute rate constants for the gas-phase H-atom abstraction by hydroxyl radicals from cyclohexane and ethane have been determined at room temperature. OH radicals were produced by pulse radiolysis of an H 2O-Ar mixture, and the decay of OH was followed by monitoring the transient light absorption around 309 nm. The rate constants were found to be k = (5.24±0.36) × 10 −12 and (2.98±0.21) × 10 −13 cm 3 molecule −1 s −1 for cyclohexane and ethane, res- pectively. These results are compared with literature data.