Determination of the Rate Constant of the Reaction of CCl 2 with HCl (original) (raw)
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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.
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).
Canadian Journal of Chemistry, 1994
The reactions of H atoms with CCl3, CF2Cl, and CH2CH2Cl radicals have been studied in a flow reactor at 300 and 475 K by observation of the infrared emission from the HCl and HF products. These reactions were observed as secondary reactions from the H + CCl3Br, CF2ClBr, and CH2Cl–CH2I chemical systems. The conditions in the flow reactor were controlled so that the nascent vibrational distributions of HCl and HF were recorded. The pattern of vibrational energy disposal to HCl was used to differentiate between Cl atom abstraction and recombination–elimination mechanisms. The H atom reactions with CCl3 and CF2Cl radicals occur only via a recombination–elimination mechanism and give HCl(υ) or HF(υ) in a unimolecular step. Thus, the Cl atom abstraction reactions must have ≥3.0 kcal mol−1 higher activation energy than the recombination reaction. From observation of the ratio of the HCl and HF products from CHF2Cl*, the difference in threshold energies for HF and HCl elimination was determ...
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%.
Quantum chemical and kinetic study of the CCl 2 self-recombination reaction
Computational and Theoretical Chemistry, 2017
The temperature and pressure dependencies of the rate constant of the recombination reaction CCl 2 + CCl 2 + M ? C 2 Cl 4 + M have been theoretically studied between 300 and 2000 K. Quantum-chemical calculations were employed to characterize relevant parts of the potential energy surface of this process. The limiting rate constants were analyzed using the unimolecular reaction theory. The resulting low pressure rate constant can be represented as k 0 = [Ar] 3.5 Â 10 À23 (T/300 K) À8.7 exp(À1560 K/T) cm 3 molecule À1 s À1. The high pressure rate constants derived from a simplified statistical adiabatic channel model (SSACM) and from a SACM combined with classical trajectory calculations (SACM/CT) are k 1 = (1.7 ± 1.0) Â 10 À12 (T/300) 0.8 ± 0.1 cm 3 molecule À1 s À1 and k 1 = (5.4 ± 3.0) Â 10 À13 (T/300) 0.7 ± 0.1 cm 3 molecule À1 s À1. The falloff curves were represented in terms of these limiting rate constants. Reported experimental results are satisfactorily described with the present model. The calculations indicate that the CCl 2 + CCl 2 reaction proceeds via the stabilization of C 2 Cl 4 , with a contribution of the C 2 Cl 3 + Cl ? C 2 Cl 4 reaction, and at sufficiently high temperatures the channel CCl 2 + CCl 2 ? C 2 Cl 2 + 2Cl becomes relevant.
Kinetic data for the reaction of hydroxyl radicals with 1,1,1-trichloroacetaldehyde at 298 ± 2 K
Chemical Physics Letters, 1994
The rate constant for the reaction of the hydroxyl radical with l,l, 1-trichloroacetaldehyde has been determined at 298 f. 2 K. Rate data were obtained at atmospheric pressure by a relative rate method. The rate constant was also measured at lower pressures (l-3.4 Torr) using the discharge flow technique with OH radical detection both by resonance fluorescence and electron paramagnetic resonance. The results provide a value of k(OH+CCI,CHO)= (1.1*0.2)x IO-'* cm3 molecule-' s-' at room temperature giving an atmospheric lifetime for CC13CH0 with respect to reaction with OH radicals of 290 h.
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.
Photoisomerization and Photoinduced Reactions in Liquid CCl 4 and CHCl 3
The Journal of Physical Chemistry A, 2013
Transient absorption spectroscopy is used to follow the reactive intermediates involved in the first steps in the photochemistry initiated by ultraviolet (266-nm wavelength) excitation of solutions of 1,5-hexadiene, isoprene and 2,3-dimethylbut-2-ene in carbon tetrachloride or chloroform. Ultraviolet and visible bands centred close to 330 nm and 500 nm in both solvents are assigned respectively to a charge transfer band of Cl-solvent complexes, and the strong absorption band of a higher energy isomeric form of the solvent molecules (iso-CCl3-Cl or iso-CHCl2-Cl). These assignments are supported by calculations of electronic excitation energies. The isomeric forms have significant contributions to their structures from charge-separated resonance forms, and offer a re-interpretation of previous assignments of the carriers of the visible bands that were based on pulsed radiolysis experiments. Kinetic analysis demonstrates that the isomeric forms are produced via the Cl-solvent complexes. Addition of the unsaturated hydrocarbons provides a reactive loss channel for the Cl-solvent complexes, and reaction radii and bimolecular rate coefficients are derived from analysis using a Smoluchowski theory model. For reactions of Cl with 1,5-hexadiene, isoprene and 2,3-dimethylbut-2-ene in CCl4, rate coefficients at 294 K are, respectively, (8.6 0.8) 10 9 M-1 s-1 , (9.5 1.6) 10 9 M-1 s-1 and (1.7 0.1) 10 10 M-1 s-1. The larger reaction radius and rate coefficient for 2,3-dimethylbut-2-ene are interpreted as evidence for an H-atom abstraction channel that competes effectively with the channel involving addition of a Cl atom to a C=C bond. However, the addition mechanism appears to dominate the reactions of 1,5-hexadiene and isoprene. Two-photon excited CCl4 or CHCl3 can also ionize the diene or alkene solute.