Kinetics and Thermochemistry of the Hydroxycyclohexadienyl Radical Reaction with O 2 : C 6 H 6 OH + O 2 ⇌ C 6 H 6 (OH)OO (original) (raw)
Related papers
Kinetics and Thermochemistry of the Reaction of 1-Chloroethyl Radical with Molecular Oxygen
The Journal of Physical Chemistry, 1995
The kinetics of the reaction CH3CHC1+ 0 2 F?. CH3CHC102products (1) has been studied at temperatures 296-839 K and He densities of (3-49) x 10l6 molecule cm-3 by laser photolysis/photoionization mass spectrometry. Rate constants were determined in time-resolved experiments as a function of temperature and bath gas density. At low temperatures (298-400 K) the rate constants are in the falloff region under the conditions of the experiments. Relaxation to equilibrium in the addition step of the reaction was monitored within the temperature range 520-590 K. Equilibrium constants were determined as a function of temperature and used to obtain the enthalpy and entropy of the addition step of the reaction (1). At high temperatures (750-839 K) the reaction rate constant is independent of both pressure and temperature within the uncertainty of the experimental data and equal to (1.2 f 0.4) x cm3 molecule-' s-'. Vinyl chloride (C2H3C1) was detected as a major product of reaction 1 at T = 800 K. The rate constant of the reaction CH3CHC1 + C12 products (6) was determined at room temperature and He densities of (9-36) x 10l6 molecule cm-3 using the same technique. The value obtained is k6 = (4.37 f 0.69) x cm3 molecule-' s-'. An estimate of the high-pressure limit for reaction 1 was determined using this measured k6 and the kl/k6 ratio obtained by Kaiser et al.:l k"1 (T=298K) = (1.04 f 0.22) x lo-" cm3 molecule-' s-'. In a theoretical part of the study, structure, vibrational frequencies, and energies of nine conformations of CH3CHC102 were calculated using ab initio UHF/6-31G* and MP2/6-31G** methods. The theoretical results are used to calculate the entropy change of the addition reaction As0298 =-152.3 f 3.3 J mol-' K-'. Th~s entropy change combined with the experimentally determined equilibrium constants resulted in a CH3CHC1-02 bond energy m 2 9 8 =-131.2 f 1.8 kJ mol-l. The rooq-temperature entropy (S O 2 9 8 = 341.0 f 3.3 J mol-' K-') and the heat of formation (A H f o~9 8 =-54.7 f 3.7 kJ mol-') of the CH3CHC102 adduct were obtained.
The Journal of Physical Chemistry A, 1998
The kinetics of the reactions CH 3 CCl 2 + O 2 h CH 3 CCl 2 O 2 f products (1) and (CH 3 ) 2 CCl + O 2 h (CH 3 ) 2 -CClO 2 f products (2) have been studied using laser photolysis/photoionization mass spectrometry. Decay constants of the radicals were determined in time-resolved experiments as a function of temperature (299-1000 K (reaction 1) and 299-700 K (reaction 2)) and bath gas density ([He] ) (3-48) × 10 16 molecules cm -3 (reaction 1) and (3-24) × 10 16 molecules cm -3 (reaction 2)). At room temperature the rate constants are in the falloff region under the conditions of the experiments. Relaxation to equilibrium in the addition step of the reaction was monitored within the temperature ranges 430-500 K (reaction 1) and 490-550 K (reaction 2). Equilibrium constants were determined as functions of temperature and used to obtain the enthalpies of the addition step of the reactions 1 and 2. At high temperatures (600-700 K) the rate constant of reaction 2 is independent of both pressure and temperature within the uncertainty of the experimental data and equal to (1.72 ( 0.24) × 10 -14 cm 3 molecule -1 s -1 . The rate constant of reaction 1 is independent of pressure within the experimental range and increases with temperature in the high-temperature region: k 1 -(791 K e T e 1000 K) ) (1.74 ( 0.36) × 10 -12 exp(-6110 ( 179 K/T) cm 3 molecule -1 s -1 . Structures, vibrational frequencies, and energies of several conformations of CH 3 CCl 2 O 2 , (CH 3 ) 2 CCl, and (CH 3 ) 2 CClO 2 were calculated using ab initio UHF/6-31G** and MP2/6-31G** methods. The results were used to calculate the entropy changes of the addition reactions: ∆S°2 98 ) -159.6 ( 4.0 J mol -1 K -1 (reaction 1) and ∆S°2 98 ) -165.5 ( 6.0 J mol -1 K -1 (reaction 2). These entropy changes combined with the experimentally determined equilibrium constants resulted in the R-O 2 bond energies: ∆H°2 98 ) 112.2 ( 2.2 kJ mol -1 (reaction 1) and ∆H°2 98 ) 136.0 ( 3.8 kJ mol -1 (reaction 2).
The Journal of Physical Chemistry a, 2004
Using a relative rate method with in situ generation of the hydroxyaldehydes, rate constants for the reactions of the OH radical with 2-hydroxybutanal [CH 3 CH 2 CH(OH)CHO], 3-hydroxybutanal [CH 3 CH(OH)CH 2 CHO], 2-hydroxypropanal [CH 3 CH(OH)CHO], 2-hydroxy-2-methylpropanal [(CH 3) 2 C(OH)CHO], and 3-hydroxypropanal [HOCH 2 CH 2 CHO] have been measured at atmospheric pressure and 296 (2 K. The hydroxyaldehydes were generated in situ from the OH radical-initiated reactions of precursor compounds (1,2-and 1,3-butanediol, 2-methyl-2,4-pentanediol, 2-methyl-3-buten-2-ol, and cis-3-hexen-1-ol) and the rate constants for the reaction of OH radicals with the hydroxyaldehydes were determined relative to those for reaction of OH radicals with the precursor compound. The rate constants obtained (in units of 10-11 cm 3 molecule-1 s-1) were CH 3 CH 2 CH(OH)CHO, 2.37 (0.23; CH 3 CH(OH)CH 2 CHO, 2.95 (0.24; CH 3 CH(OH)CHO, 1.70 (0.20; (CH 3) 2 C(OH)CHO, 1.40 (0.25; and HOCH 2 CH 2 CHO, 1.99 (0.29.
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 .
The Journal of Physical Chemistry, 1991
The kinetics of reaction 1, CCI, + O2 + M-CCI3O2 + M, has been investigated in detail as a function of temperature and Over a large pmure range. At low pressure, 0.8-12 Torr, the reaction was investigated by laser photolysis and timeresolved mass spectrometry, while at high pressure (760 Torr), flash photolysis with UV absorption spectrometry was employed. At the low-pressure limit, the rate expression, k,(O) = (1.6 f 0.3) X 10-'(T/298)*6.3fo") cm6 molecule-2 s-' (M = N2), exhibits a quite strong negative temperature coefficient. The obtained strong collision rate expression, 7.0 X T/298y3 cm6 molecule-2 s-I, using either RRKM calculations or Troe's factorized expression, is unable to reproduce the experimental temperature dependence, unless an unreasonably strong temperature dependence is assigned to the collisional efficiency factor: = 0.23(T/298)-2.0 (M = N2). Similar results are obtained for other chlorofluoromethyl radicals. The falloff curves were constructed by using RRKM calculations obtained by adjusting 8, and the transition-state model, in order to reproduce the experimental data. The rate expression at the high-pressure limit was derived from these calculations kl(-) = (3.2 i 0.7) X 10-'2(T/298)-(1.2M.4) cm3 molecule-I s-l. All the parameters to be used in Troe's analytical expression for calculating the bimolecular rate constant at any pressure and temperature are given. The rate constant at the low-pressure limit kl(0) is more than an order of magnitude lower than for the CF, radical. The RRKM calculations show that this arises from a large difference in the CO bond dissociation energies in the corresponding peroxy radicals: 81.9 kJ mol-] for CC1302 instead of-145 kJ mol-' for CF3O2.
The Journal of Physical Chemistry A, 1999
By using 193 nm laser photolysis and cavity ring-down spectroscopy to produce and monitor the propargyl radical (CH 2 CCH), the self-reaction and oxygen termolecular association rate coefficients for the propargyl radical were measured at 295 K between total pressures of 300 Pa and 13300 Pa (2.25 and 100 Torr) in Ar, He, and N 2 buffer gases. The rate coefficients obtained by simple second-order fits to the decay data were observed to vary with the photolytic precursors: allene, propargyl chloride, and propargyl bromide. By using a numerical fitting routine and more comprehensive mechanisms, a distinct rate coefficient for the selfreaction was determined, k ∞ (C 3 H 3 +C 3 H 3)) (4.3 (0.6) × 10-11 cm 3 molecule-1 s-1 at 295 K. This rate coefficient, which is a factor of 2.8 times slower than reported previously, was independent of total pressure and buffer choice over the entire pressure range. Other rate coefficients derived during the modeling included k(C 3 H 3 +H 665 Pa He)) (2.5 (1.1) × 10-10 cm 3 molecule-1 s-1 , k(C 3 H 3 +C 3 H 3 Cl 2)) (7 (4) × 10-11 cm 3 molecule-1 s-1 , and k(C 3 H 3 +C 3 H 3 Br 2)) (2.4 (2) × 10-11 cm 3 molecule-1 s-1. The association reaction C 3 H 3 + O 2 was found to lie in the falloff region between linear and saturated pressure dependence for each buffer gas (Ar, He, and N 2) between 300 Pa and 13300 Pa. A fit of these data derived the high-pressure limiting rate coefficient k ∞ (C 3 H 3 +O 2)) (2.3 (0.5) × 10-13 cm 3 molecule-1 s-1. Three measurements of the propargyl radical absorption cross-section obtained σ 332.5) (413 (60) × 10-20 cm 2 molecule-1 at 332.5 nm. Stated uncertainties are two standard deviations and include the uncertainty of the absorption cross section, where appropriate.
Proceedings of the Combustion Institute, 2021
We have used laser-photolysis/photoionization mass spectrometry to measure the kinetics of the reaction of 1-methylpropargyl (but-3-yn-2-yl, CH = C −CH-CH 3) radicals with oxygen molecules as a function of temperature (T = 200 − 685 K) and bath gas density (1. 2 − 15 × 10 16 cm −3). The low temperature (T ≤ 304 K) kinetics is dominated by oxygen addition to the −CHcarbon of the radical to form a peroxyl radical, and the measured CH = C −CH-CH 3 + O 2 bimolecular rate coefficient exhibits negative temperature dependence and depends on bath gas density. At slightly higher temperatures (335 − 396 K), where the redissociation rate of the peroxyl is already observable, we measured the CH = C = CH-CH 3 + O 2 − − − − CH ≡C-C (OO •)H-CH 3 equilibrium constant as a function of temperature. At even higher temperatures (T = 479 − 685 K), the loss rate of 1-methylpropargyl is determined by the addition of oxygen to the terminal H-C = carbon and the reaction is observed to produce methylketene. The high-temperature CH = C −CH-CH 3 + O 2 bimolecular rate coefficient is independent of bath gas density and the temperature dependence is weakly positive. To explain our experimental findings, we performed quantum chemical calculations together with master equation simulations. By using our experimental data to constrain key parameters, the master equation model was able to reproduce experimental results reasonably well. We then extended the conditions of our simulations up to 2000 K and 100 bar. The results of these simulations are provided in ChemKin compatible PLOG format.
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.
Kinetics and thermochemistry of the reaction of 3-methylpropargyl radical with molecular oxygen
Proceedings of the Combustion Institute, 2019
We have measured the kinetics and thermochemistry of the reaction of 3-methylpropargyl radical (but-2-yn-1-yl) with molecular oxygen over temperature (223 − 681 K) and bath gas density (1.2 − 15.0 × 10 16 cm −3) ranges employing photoionization mass-spectrometry. At low temperatures (223 − 304 K), the reaction proceeds overwhelmingly by a simple addition reaction to the −CH 2 end of the radical, and the measured CH 3 CCCH • 2 + O 2 reaction rate coefficient shows negative temperature dependence and depends on bath gas density. At intermediate temperatures (340−395 K), the addition reaction equilibrates and the equilibrium constant was determined at different temperatures. At high temperatures (465 − 681 K), the kinetics is governed by O 2 addition to the third carbon atom of the radical, and rate coefficient measurements were again possible. The high temperature CH 3 CCCH • 2 + O 2 rate coefficient is much smaller than at low T , shows positive temperature dependence, and is independent of bath gas density. In the intermediate and high temperature ranges, we observe a formation signal for ketene (ethenone). The reaction was further investigated by combining the experimental results with quantum chemical calculations and master equation modeling. By making small adjustments (2 − 3 kJ mol −1) to the energies of two key transition states, the model reproduces the experimental results within uncertainties. The experimentally constrained master equation model was used to simulate the CH 3 CCCH • 2 + O 2 reaction system at temperatures and pressures relevant to combustion.