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Download Free PDFKinetics and thermochemistry of the hydroxycyclohexadienyl radical reaction with O2: C6H6OH + O2 ? C6H6(OH)OOLev Krasnoperov

2004, The Journal of Physical Chemistry a

https://doi.org/10.1021/JP030935Cvisibility

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Abstract

The UV absorption spectrum along with the self-reaction and oxidation reaction kinetics of the hydroxycyclohexadienyl radical, C 6 H 6 OH (which results from OH addition to benzene), were studied using excimer laser photolysis coupled to transient UV absorption. The radicals were generated by photolysis of N 2 O/H 2 O/ C 6 H 6 /He mixtures at 193 nm in a series of chemical reactions initiated by O( 1 D). The radical has continuous absorption in the range 260-340 nm with a maximum absorption cross-section of (8.1 ( 1.4) × 10 -18 cm 2 molecule -1 at 280 nm. Reaction of the radical with molecular oxygen, C 6 H 6 OH + O 2 h C 6 H 6 (OH)OO (1), and self-reaction C 6 H 6 OH + C 6 H 6 OH f products (2), were studied over the 252-285 K temperature range at 1.01 ( 0.02 bar (He). The radical temporal profiles were recorded via transient absorption at 315 nm. In reaction 1, two-time-domain "equilibration" kinetics were recorded in the temperature range 252-273 K. The rate constant of the addition reaction is k 1 ) (1.4 ( 0.8) × 10 -12 exp(-18.6 ( 1.7 kJ mol -1 /RT) cm 3 molecule -1 s -1 . The standard enthalpy of reaction 1 was determined from the measured equilibrium constants using the third law method: ∆H°2 98 ) -43.6 ( 2.0 kJ mol -1 . The measured rate constant of self-reaction 2 is k 2 ) (6 ( 3) × 10 -11 exp(-2.00 ( 1.6 kJ mol -1 /RT) cm 3 molecule -1 s -1 .

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downloadDownload free PDFView PDFchevron_rightKinetics of the Reactions of CH₂Cl, CH₃CHCl, and CH₃CCl₂ Radicals with Cl₂ in the Temperature Range 191−363 KRaimo Timonen

Journal of Physical Chemistry A, 2010

The kinetics of three chlorinated free radical reactions with Cl 2 have been studied in direct time-resolved measurements. Radicals were produced in low initial concentrations by pulsed laser photolysis at 193 nm, and the subsequent decays of the radical concentrations were measured under pseudo-first-order conditions using photoionization mass spectrometer (PIMS). The bimolecular rate coefficients of the CH 3 CHCl + Cl 2 reaction obtained from the current measurements exhibit negative temperature dependence and can be expressed by the equation k(CH 3 CHCl + Cl 2)) ((3.02 (0.14) × 10-12)(T/300 K)-1.89(0.19 cm 3 molecule-1 s-1 (1.7-5.4 Torr, 191-363 K). For the CH 3 CCl 2 + Cl 2 reaction the current results could be fitted with the equation k(CH 3 CCl 2 + Cl 2)) ((1.23 (0.02) × 10-13)(T/300 K)-0.26(0.10 cm 3 molecule-1 s-1 (3.9-5.1 Torr, 240-363 K). The measured rate coefficients for the CH 2 Cl + Cl 2 reaction plotted as a function of temperature show a minimum at about T) 240 K: first decreasing with increasing temperature and then, above the limit, increasing with temperature. The determined reaction rate coefficients can be expressed as k(CH 2 Cl + Cl 2)) ((2.11 (1.29) × 10-14) exp(773 (183 K/T)(T/300 K) 3.26(0.67 cm 3 molecule-1 s-1 (4.0-5.6 Torr, 201-363 K). The rate coefficients for the CH 3 CCl 2 + Cl 2 and CH 2 Cl + Cl 2 reactions can be combined with previous results to obtain: k combined (CH 3 CCl 2 + Cl 2)) ((4.72 (1.66) × 10-15) exp(971 (106 K/T)(T/300 K) 3.07(0.23 cm 3 molecule-1 s-1 (3.1-7.4 Torr, 240-873 K) and k combined (CH 2 Cl + Cl 2)) ((5.18 (1.06) × 10-14) exp(525 (63 K/T)(T/300 K) 2.52(0.13 cm 3 molecule-1 s-1 (1.8-5.6 Torr, 201-873 K). All the uncertainties given refer only to the 1σ statistical uncertainties obtained from the fitting, and the estimated overall uncertainty in the determined bimolecular rate coefficients is about (15%.

downloadDownload free PDFView PDFchevron_rightOxidation of dimethyl ether: Absolute rate constants for the self reaction of CH3OCH2 radicals, the reaction of CH3OCH2 radicals with O2, and the thermal decomposition of CH3OCH2 radicalsOle John Nielsen

International Journal of Chemical Kinetics, 1997

The rate constant for the reaction of CH 3 OCH 2 radicals with O 2 (reaction (1)) and the self reaction of CH 3 OCH 2 radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k 1 was studied at 296 K over the pressure range 0.025-1 bar and in the temperature range 296-473 K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: (k prod) (k RO2) where k RO2 is the rate constant for peroxy radical production and k prod is the rate constant for formaldehyde production. The k 1 values obtained at 296 K together with the available literature values for k 1 determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: cm 6 cm 3 and cm 3 where k RO2,0 and k RO2,ϱ are the overall termolecular and bimolecular rate constants for formation of CH 3 OCH 2 O 2 rad-s Ϫ1 molecule Ϫ1 k prod,0 ϭ (6.0 Ϯ 0.5) ϫ 10 Ϫ12 s Ϫ1 , molecule Ϫ1 k RO2,ϱ ϭ (1.14 Ϯ 0.04) ϫ 10 Ϫ11 s Ϫ1 , molecule Ϫ2 k RO2,0 ϭ (9.4 Ϯ 4.2) ϫ 10 Ϫ30 k 1 ϭ k RO2 ϩ k prod , CH 3 OCH 2 O 2 # ϩ M 9: CH 3 OCH 2 O 2 ϩ M CH 3 OCH 2 ϩ O 2 ;: CH 3 OCH 2 O 2 # 9: CH 2 OCH 2 O 2 H # 9: 2HCHO ϩ OH CH 3 OCH 2 ϩ O 2 ;: 628 SEHESTED ET AL. icals and k prod,0 represents the bimolecular rate constant for the reaction of CH 3 OCH 2 radicals with O 2 to yield formaldehyde in the limit of low pressure. exp cm 3 was determined at 18 bar total pressure over the temperature range 296-473 K. At 1 bar total pressure and 296 K, cm 3 and at 18 bar total pressure over the temperature range 296-523 K, cm 3 As a part of this study the decay rate of CH 3 OCH 2 radicals was used to study the thermal decomposition of CH 3 OCH 2 radicals in the temperature range 573-666 K at 18 bar total pressure. The observed decay rates of CH 3 OCH 2 radicals were consistent with the literature value of The results are discussed in the context of dimethyl ether as an alternative diesel fuel.

downloadDownload free PDFView PDFchevron_rightA Kinetic Study On The Reactions Of OH Radicals With Esters And Alkoxy EstersStéphane Le Calvé

WIT Transactions on Ecology and the Environment, 1970

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