Addition and recombination reactions of unsaturated radicals using a novel laser kinetics spectrometer (original) (raw)
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The Journal of Physical Chemistry A, 1997
A laser photolysis reactor that uses cavity ring-down spectroscopic (CRDS) detection was characterized and used to measure the rate coefficients of three benchmark reactions of known importance to ethane oxidation. At 295 K and approximately 700 Pa (5.5 Torr) total pressure, we obtained the self-reaction rate coefficients of k ) (1.99 ( 0.44) × 10 -11 cm 3 molecule -1 s -1 for C 2 H 5 + C 2 H 5 and k ) (7.26 ( 2.4) × 10 -14 cm 3 molecule -1 s -1 for C 2 H 5 O 2 + C 2 H 5 O 2 . We obtained k ) (2.7 ( 0.3) × 10 -12 cm 3 molecule -1 s -1 for the pseudo-first-order association reaction O 2 + C 2 H 5 + Ar. We also measured the absorption cross sections of the ethyl radical, σ 220 ) (252 ( 42) × 10 -20 cm 2 molecule -1 and σ 222 ) (206 ( 42) × 10 -20 cm 2 molecule -1 . Stated uncertainties are 2σ. The new rate coefficients agree with those obtained previously by other methods. The agreement confirms that ultraviolet CRDS detection is a viable tool for experimental determinations of gas-phase radical-radical and radical-molecule reaction rate coefficients.
Proceedings of The Combustion Institute, 2005
Several elementary reactions of formyl radical of combustion importance were studied using pulsed laser photolysis coupled to transient UV–Vis absorption spectroscopy: HCO → H + CO (1), HCO + HCO → products (2), and HCO + CH3 → products (3). One-pass UV absorption, multi-pass UV absorption as well as cavity ring-down spectroscopy in the red spectral region were used to monitor temporal profiles of HCO radical. Reaction (1) was studied over the buffer gas (He) pressure range 0.8–100 bar and the temperature range 498–769 K. Reactions , , , and as well as the UV absorption spectrum of HCO, were studied at 298 and 588 K, and the buffer gas (He) pressure of 1 bar. Pulsed laser photolysis (308, 320, and 193 nm) of acetaldehyde, propionaldehyde, and acetone was used to prepare mixtures of free radicals. The second-order rate constant of reaction (1) obtained from the data at 1 bar is: k1(He) = (0.8 ± 0.4) × 10−10exp(−(66.0 ± 3.4) kJ mol−1/RT) cm3 molecule−1 s−1. The HCO dissociation rate constants measured in this work are lower than those reported in the previous direct work. The difference is a factor of 2.2 at the highest temperature of the experiments and a factor of 3.5 at the low end. The experimental data indicate pressure dependence of the rate constant of dissociation of formyl radical 1, which was attributed to the early pressure fall-off expected based on the theory of isolated resonances. The UV absorption spectrum of HCO was revised. The maximum absorption cross-section of HCO is (7.3 ± 1.2) × 10−18 cm2 molecule−1 at 230 nm (temperature independent within the experimental error). The measured rate constants for reactions , , , and are: k2 = (3.6 ± 0.8) × 10−11 cm3 molecule−1 s−1 (298 K); k3 = (9.3 ± 2.3) × 10−11 cm3 molecule−1 s−1(298 and 588 K).
Kinetics of the Methyl–Vinyl Radical + O2 Reactions Associated with Propene Oxidation
Journal of Physical Chemistry A, 2019
The bimolecular rate coefficients of reactions CH 3 CCH 2 + O 2 (1) and cis/trans-CH 3 CHCH + O 2 (2a/3a) have been measured using a tubular laminar flow reactor coupled with a photoionization mass spectrometer (PIMS). These reactions are relevant in the combustion of propene. Pulsed excimer laser photolysis of a ketone or a bromide precursor molecule at 193 or 248 nm wavelength was used to produce radicals of interest homogeneously along the reactor. Timeresolved experiments were performed under pseudo-first-order conditions at low pressure (0.3−1.5 Torr) over the temperature range 220−660 K. The measured bimolecular rate coefficients were found to be independent of bath gas concentration. The bimolecular rate coefficients possess negative temperature dependence at low temperatures (T < 420 K) and appear to be independent of temperature at high temperatures (T > 420 K). Observed products of the reaction CH 3 CCH 2 + O 2 were CH 3 and H 2 CO, while for the reaction cis/trans-CH 3 CHCH + O 2 , observed products were CH 3 CHO and HCO. Current results indicate that the reaction mechanism of both reactions is analogous to that of C 2 H 3 + O 2. Methyl substitution of the vinyl radical changes its reactivity toward O 2 upward by ca. 50% if it involves the α-position and downward by ca. 30% if the methyl group takes either of the β-positions, respectively.
Reaction Kinetics and Catalysis Letters, 2001
... Ákos Bencsura, Krisztina Imrik, Sándor Dóbé and Tibor Bérces Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences Pusztaszeri út. 59-67, H-1025 Budapest, Hungary ... Phys. Letters, 319, 521 (2000). 8. I. Szilágyi, K. Imrik, S. Dóbé, T. Bérces: Ber. ...
Journal of Physical Chemistry A, 2005
The laser-induced fluorescence (LIF) excitation spectra of the 4-methylcyclohexoxy and d11-cyclohexoxy radicals have been measured for the first time. LIF intensity was used as a probe in direct kinetic studies of the reaction of O 2 with trans-4-methylcyclohexoxy and d11-cyclohexoxy radicals from 228 to 301 K. Measured rate constants near room temperature are uniformly higher than the Arrhenius fit to the lower-temperature data, which can be explained by the regeneration of cyclic alkoxy radicals from the product of their-scission and the effect of O 2 concentration on the extent of regeneration. The Arrhenius expressions obtained over more limited ranges were k O 2) (1.4-1 +8) × 10-13 exp[(-810 (400)/T] cm 3 molecule-1 s-1 for trans-4methylcyclohexoxy (228-292 K) and k O 2) (3.7-1 +4) × 10-14 exp)[(-760 (400) /T] cm 3 molecule-1 s-1 for d11-cyclohexoxy (228-267 K) independent of pressure in the range 50-90 Torr. The room-temperature rate constant for the reaction of trans-4-methylcyclohexoxy radical with O 2 (obtained from the Arrhenius fit) is consistent with the commonly recommended value, but the observed activation energy is ∼3 times larger than the recommended value of 0.4 kcal/mol and half the value previously found for the reaction of normal cyclohexoxy radical with O 2 .
Ultraviolet absorption spectra and kinetics of CH3S and CH2SH radicals
Chemical Physics Letters, 1991
Acetonyl radicals and acetonylpcroxy radicals were produced by pulse radiolysis of gas mixtures with varying concentrations of CI-I&OCH, and Oz in 1 atm of SF6 to initiate tlte reactions ( 1) F+CI-IsCOCH3-+HFfCH@CH~, (2) ZCH&OCH,-products, (3 ) CHJCOCH2+02( + M)&I-ISCOCH202( + M) and (4) 2CHsCOCHLOL+products. The ultraviolet absorption spectrum of the acetonyl radical is composed of a fairly weak band centered at 3 15 nm and a stronger band in the range of 200-250 nm. The absorption cross section has been determined, a(310 nm)=(8.73~0.50)x10-1g cm* molecule-L. The values k2= (4.8f0.4) x lo-", k,= (1.5+0.3)x lo-'* and k4= (8.3f 1.6) x 10-'zcm3 molecule-' s-' at 298 K were derived by computer modelling of the observed kinetic features. 206 0009-2614/90/$03.50 0 1990 -Elsevier Science Publishers B.V. (North-Holland) volume 173, number 2,3 CHEMICAL PHYSICS LETTERS
Kinetic Study of the CCl2 Radical Recombination Reaction by Laser‐Induced Fluorescence Technique
International Journal of Chemical Kinetics, 2013
ABSTRACTAn experimental setup that coupled IR multiple‐photon dissociation (IRMPD) and laser‐induced fluorescence (LIF) techniques was implemented to study the kinetics of the recombination reaction of dichlorocarbene radicals, CCl2, in an Ar bath. The CCl2 radicals were generated by IRMPD of CDCl3. The time dependence of the CCl2 radicals’ concentration in the presence of Ar was determined by LIF. The experimental conditions achieved allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C2Cl4. The rate constant for this reaction was determined in both the falloff and the high‐pressure regimes at room temperature. The values obtained were k0 = (2.23 ± 0.89) × 10−29 cm6 molecules−2 s−1 and k∞ = (6.73 ± 0.23) × 10−13 cm3 molecules−1 s−1, respectively.