- Ultrafast absorption spectroscopy of photodissociated CF2Br2: Details of the reaction mechanism and evidence for anomalously slow intramolecular vibrational redistribution within the CF2Br intermediate
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Ultrafast time-resolved absorption spectroscopy in the hard ultraviolet has been used to investigate the photodissociation of gas-phase CF2Br2 photolyzed at 248 nm.The broadband spectra obtained in the 250-265 nm region have shown that absorption of a single photon activates a two-step sequential elimination of the molecule's two bromine atoms, leaving the product CF2 radical in the ground or first-excited vibrational state of its ν2 bending mode.The spectra also demonstrate the direct detection of the vibrationally hot CF2Br intermediate species itself.We interpret the 6 ps time scale over which the diffuse CF2Br spectrum evoles as evidence for slow intramolecular vibrational redistribution within this molecule.
- Gosnell, T. R.,Taylor, A. J.,Lyman, J. L.
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- Photodissociation dynamics of the reaction CF2Br2 + hv → CF2 + 2Br. Energetics, threshold and nascent CF2 energy distributions for λ = 223-260 nm
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The dissociation dynamics of the reaction CF2Br2 + hv → CF2 + 2 Br have been studied for a variety of dissociation energies, E(diss) = 460-535 kJ mol-1 (corresponding to λ = 260-223 nm). The laser induced fluorescence spectrum of nascent CF2 products was measured for various dissociation energies within this range. Analysis of the spectra yielded the CF2 vibrational distribution and average rotational energy. The translational energy of CF2 was measured via the Doppler broadening of various fully resolved rovibronic transitions. The most detailed analysis of energy disposal in the CF2 fragments was carried out at E(diss) = 486 kJ mol-1 (or λ = 246 nm). At this energy each degree of freedom of CF2 had an average energy of E(vib) = 0.4 ± 0.2 kJ mol-1, E(rot) = 2.5 ± 0.5 kJ mol-1, and E(trans) = 24 ± 3 kJ mol-1. These CF2 energies, coupled with the available thermochemical data, allow us to determine unambiguously that CF2 production must be accompanied by the production of two atomic Br fragments. A photofragment excitation spectrum of CF2Br2, probing for the production of CF2 fragments, provided a reaction threshold of 460 ± 3 kJ mol-1 (corresponding to 260 ± 1.5 nm). The range of previously published reaction enthalpies varies from 392 to 438 kJ mol-1, all of which are substantially below the observed threshold. Additionally, at E(diss) = 486 kJ mol-1, the energy of the CF2 fragment was 27 kJ mol-1 on average, already in excess of the available 26 kJ mol-1, and without considering the kinetic energy of the recoiling Br atoms. We rationalise these data by proposing that the reaction might have a small barrier in the exit channel. The observed threshold corresponds to the top of the barrier (460 kJ mol- 1), while the final energy in the fragments is determined by the asymptotic reaction energy (~ 424 kJ mol-1). Simple dynamical models are presented to show that the proposed mechanism is reasonable. Key future experiments and calculations are identified that would enable a clearer picture of the dynamics of this reaction.
- Cameron, Melanie R.,Johns, Stephen A.,Metha, Gregory F.,Kable, Scott H.
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- Reaction of Trifluoromethyl Iodide on Ni(100)
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We have studied the surface chemistry of trifluoromethyl iodide adsorbed on Ni(100) under ultrahigh-vacuum conditions.Temperature-programmed desorption and reflection absorption infrared spectroscopy were used to determine gas-phase products and species formed at the surface.Several reaction products were found from trifluoromethyl iodide dissociation on Ni(100).Iodine atoms and nickel fluoride, NiF2, desorb at high temperatures near 1000 and 800 K, respectively.At high coverages, carbon-containing species desorb from the surface as well.CF3I and CF3 desorb at 168/136 K (mono/multilayer) and 316 K, respectively.In the presence of background hydrogen, HF and CH2F2, are also detected in temperature-programmed desorption at 178 and 235 K, respectively.The infrared spectra of multilayer, monolayer, and submonolayer coverages of CF3I on the surface and adsorbed CFx groups have been measured.The temperature-programmed desorption and infrared data show that both carbon-iodine and carbon-fluorine bonds are readily activated on nickel at low temperatures.It is estimated that approximately 90percent of adsorbed CF3I decomposes on Ni(100).
- Myli, K. B.,Grassian, V. H.
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- Competition between unimolecular C-Br-bond fission and Br2 elimination in vibrationally highly excited CF2Br2
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The competition between C-Br-bond fission and three-center elimination of molecular bromine (Br2) in highly excited CF2Br2 molecules has been studied under collision-free conditions.Transient resonantly enhanced multiphoton ionization (REMPI) was used to monitor Br(2P1/2) and Br(2P3/2) formation during and after infrared (IR) mutiphoton excitation of CF2Br2; time-resolved laser-induced fluorescence (LIF) spectroscopy was employed for the detection of transient CF2 after Br2 elimination.Direct time-resolved measurements of the sum of afterpulse reaction rates, absolute product yields for the CF2 and Br(2P3/2) channels as well as absorbed energies per excitation pulse were used to characterize parts of the vibrational energy distribution P(E) established after IR multiphoton excitation and to determine rate coefficients and branching ratios for the elimination and dissociation reaction as a function of the average internal energy .The existence of both channels, the dissociation and the elimination channel, has been confirmed.A comparison of the experimental data with statistical adiabatic channel model calculations (SACM) enabled us to determine the threshold energies E0(J=0) for the unimolecular Br2 elimination 0(J=0) = 19 070+/-500 cm-1> and the C-Br bond fission 0(J=0) = 20 700+/-500 cm-1>, the two possible pathways of the reaction.
- Abel, B.,Hippler, H.,Lange, N.,Schuppe, J.,Troe, J.
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- Halomethylenes: Effects of Halogen Substitution on Absolute Heats of Formation
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New values for the heats of formation of CF2, CCl2, CClF, CFH, and CClH have been derived from estimations of the thermochemistry of the reaction(s) CXYH+ + B -> CXY + BH+ where X and Y are F and/or Cl and B is a molecule for which an absolute value of the gas-phase basicity (or proton affinity) is available.The experiments, carried out in an ion cyclotron resonance spectrometer, lead to the following values for the heats of formation (in kcal/mol) of the ground-state singlet carbenes: CF2, -49 +/- 3; CCl2, 39 +/- 3; CFCl, -2 +/- 7; CFH, 26 +/-3; CClH, 71 +/-5.The value for CF2 is lower by about 5 kcal/mol than the previously accepted value, but in good agreement with values derived from previous "bracketing" results and also in agreement with values derived from the observed threshold energies for ionic dissociation processes.The value for CCl2 is significantly lower than the 1976 value of 47 +/-3 kcal/mol recommended by S.W.Benson, but in good agreement with an earlier value (40 +/- 5 kcal/mol) recommended by this author with more recent experimental results on the onset energy of formation of Cl2- from CCl4.The values for CFH, CClH, and CFCl are all approximately equal to the averages of the heats of formation of the corresponding CX2 and CY2 species, in agreement with assumptions made in previous estimates of these quantities.Values for the C-X bond energies in the halomethylenes, the heats of formation of the corresponding CXY+ ions, and the ionization potentials of the CXY species are derived from the results.From the most recent calculations of the energy differences between the ground-state singlet halomethylenes and the first triplet state, values for the heats of formation of the triplet halomethylenes are obtained; an analysis of trends in these values indicates that 3CF2 is substantially destabilized.
- Lias, Sharon G.,Karpas, Zeev,Liebman, Joel F.
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- The kinetics of the CF3 + CF3 and CF3 + F combination reactions at 290 K and at He-pressures of ≈ 1-6 Torr
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The rate constants for the combination reactions CF3 + CF 3 and CF3 + F at 290 K and helium pressures of ≈ 1-6 Torr have been determined, using clean chemical sources of CF3, by means of discharge flow-molecular beam sampling-threshold ionisation mass spectrometry (DF/MB-TIMS). For the mutual reaction of CF3, no pressure dependence could be observed over the 1-6 Torr pressure range, indicating that the obtained rate constant of k1∞ = (1.8 ± 0.6) × 10-12 cm3 s-1 is the high pressure limit. This result, which agrees with the lowest values in literature but is ca. five times smaller than the most recent data, is fully in line with the known trend in the mutual reaction rate constant for the series CH3; CH2F; and CHF2. The reaction of CF 3 with F was found to exhibit a clear pressure dependence in the 0.5 to 6 Torr range. Using a Troe fall-off formalism, the low-pressure limit rate constant was determined as k20(He) = (1.47 ± 0.24) × 10-28 cm6 s-1 differing substantially from the only available previous determination; a variational transition state theoretical treatment is shown to support our data. The Owner Societies 2005.
- Dils, Bart,Vertommen, Johan,Carl, Shaun Avondale,Vereecken, Luc,Peeters, Jozef
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- Shock wave studies of the pyrolysis of fluorocarbon oxygenates. II. the thermal dissociation of C4F8O
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The thermal decomposition of octafluorooxalane, C4F8O, to C2F4 + CF2 + COF2 has been studied in shock waves highly diluted in Ar between 1300 and 2200 K. The primary dissociation was shown to be followed by secondary dissociation of C2F4 and dimerization of CF2. The primary dissociation was found to be in its falloff range and falloff curves were constructed. The limiting low and high pressure rate constants were estimated and compared with modelling results. Quantum-chemical calculations identified possible reaction pathways, either leading directly to the final products of the reaction or passing through an open-chain CF2CF2CF2 intermediate which dissociates in a second step.
- Cobos,Hintzer,S?lter,Tellbach,Thaler,Troe
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p. 3159 - 3164
(2017/08/17)
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- Shock wave studies of the pyrolysis of fluorocarbon oxygenates. I. The thermal dissociation of C3F6O and CF3COF
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The thermal decomposition of hexafluoropropylene oxide, C3F6O, to perfluoroacetyl fluoride, CF3COF, and CF2 has been studied in shock waves highly diluted in Ar between 630 and 1000 K. The measured rate constant k1 = 1.1 × 1014exp(-162(±4) kJ mol-1/RT) s-1 agrees well with literature data and modelling results. Using the reaction as a precursor, equimolar mixtures of CF3COF and CF2 were further heated. Combining experimental observations with theoretical modelling (on the CBS-QB3 and G4MP2 ab initio composite levels), CF3COF is shown to dissociate on two channels, either leading to CF2 + COF2 or to CF3 + FCO. By monitoring the CF2 signals, the branching ratio was determined between 1400 and 1900 K. The high pressure rate constants for the two channels were obtained from theoretical modelling as k5,∞(CF3COF → CF2 + COF2) = 7.1 × 1014exp(-320 kJ mol-1/RT) s-1 and k6,∞(CF3COF → CF3 + FCO) = 3.9 × 1015exp(-355 kJ mol-1/RT) s-1. The experimental results obtained at [Ar] ≈ 5 × 10-6 mol cm-3 were consistent with modelling results, showing that the reaction is in the falloff range of the unimolecular dissociation. The mechanism of secondary reactions following CF3COF dissociation has been analysed as well.
- Cobos,Hintzer,S?lter,Tellbach,Thaler,Troe
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p. 3151 - 3158
(2017/08/17)
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- Difluorocarbene studied with threshold photoelectron spectroscopy (TPES): Measurement of the first adiabatic ionization energy (AIE) of CF2
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The first photoelectron band of difluorocarbene CF2, has been studied by threshold photoelectron (TPE) spectroscopy. CF2 was prepared by microwave discharge of a flowing mixture of hexafluoropropene, C3F6, and argon. A vibrationally resolved band was observed in which at least twenty-two components were observed. In the first PE band of CF2, the adiabatic ionization energy differs significantly from the vertical ionization energy because, for the ionization CF 2+ (X2A1)+e- ← CF2 (X1A1), there is an increase in the FCF bond angle (by ≈20°) and a decrease in the C-F bond length (by ≈ 0.7 A). The adiabatic component was not observed in the experimental TPE spectrum. However, on comparing this spectrum with an ab initio/Franck-Condon simulation of this band, using results from high-level ab initio calculations, the structure associated with the vibrational components could be assigned. This led to alignment of the experimental TPE spectrum and the computed Franck-Condon envelope, and a determination of the first adiabatic ionization energy of CF2 as (11.362± 0.005) eV. From the assignment of the vibrational structure, values were obtained for the harmonic and fundamental frequencies of the symmetric stretching mode (v1′) and symmetric bending mode (v2′) in CF2+ (X2A1).
- Innocenti, Fabrizio,Eypper, Marie,Lee, Edmond P. F.,Stranges, Stefano,Mok, Daniel K. W.,Chau, Foo-Tim,King, George C.,Dyke, John M.
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experimental part
p. 11452 - 11460
(2009/12/03)
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- Rate measurement of the reaction of CF2Cl radicals with O 2
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We have studied the association reaction of the CF2Cl radicals with O2 in presence of N2. The infrared multiple photon dissociation (IRMPD) technique with a homemade TEA CO2 laser was used for the CF2Cl radical generation and the vibrational chemiluminiscence technique was set up for the study of the reaction kinetics. The time-resolved IR fluorescence of the vibrationally excited CF2O photoproduct was used to measure the disappearance rate of these radicals. A kinetic mechanism is presented to account for the rate of production of CF 2O*. The CF2Cl radical association reaction rate with O2, evidence of a direct channel of photoproduct formation and its reaction rate, and the CF2O* collisional deactivation rate have been obtained.
- Codnia, Jorge,Azcarate, Maria Laura
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p. 755 - 762
(2008/02/11)
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- Intermediates of thermal transformations of perfluoro-organic compounds. New spectral data and reactions
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New completely fluorinated intermediates were identified from spectroscopic studies of thermal reactions of perfluoro-olefins, some carbocycles, and perfluoro-oxiranes in the gas phase. Detailed mechanisms of several complex reactions were established. For example, the mechanism of higher perfluoro-olefin synthesis from lower species under pyrolysis was established. Following this mechanism the first stage is the reversible reaction of biradicaloid formation which are isomeric to perfluoro-olefins. It was shown that biradicaloids are the primary intermediates in recombination of singlet completely fluorinated carbenes.
- Buravtsev, Nikolay N.,A. Kolbanovsky, Yuly
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- Photodissociation dynamics of 1,1-difluoroethylene at 157 nm excitation
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Photodissociation of 1,1-difluoroethylene (F2CCH2) at 157 nm has been investigated using photofragment translational spectroscopy. Five dissociation channels have been experimentally observed; molecular HF elimination, H atom elimination, molecular hydrogen (H2) elimination, F atom elimination, and double bond breaking. Molecular HF elimination and H atom elimination channels are found to be the two major dissociation pathways in photodissociation of F2CCH2 at 157 nm excitation. Molecular hydrogen (H2) elimination and double bond cleavage are also significant, while F atom elimination is a minor process. Product translational energy distributions for all dissociation channels have also been measured. All translational energy releases are peaked at energies away from zero, indicating that the dissociation of F2CCH2 at 157 nm excitation most likely occurs with exit barriers on the ground electronic potential surface through internal conversion from the initially excited electronic state. Branching ratios and averaged energy partitions for different channels have also been estimated.
- Lin,Wu,Hwang,Lee,Yang
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p. 10838 - 10846
(2007/10/03)
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- Photodissociation dynamics of trifluoroethylene at 157 nm excitation
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Photodissociation of trifluoroethylene (F2CCFH) at 157 nm has been investigated using photofragment translational spectroscopy. Four dissociation channels have been experimentally observed: molecular HF elimination, H atom elimination, F atom e
- Lin,Hsu,Hwang,Lee,Yang
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p. 10719 - 10726
(2007/10/03)
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- Infrared multiphoton dissociation of two perfluorobutenes
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Photofragment translational spectroscopy was used to examine the infrared multiphoton dissociation of octafluoro-1-butene and octafluoro-2-butene. The predominant unimolecular reaction in octafluoro-1-butene at moderate laser fluences is cleavage of a carbon-carbon single bond to give the products CF3 and C3F5. The two other reactions that take place are CF2 elimination and the formation of equal weight fragments with the chemical composition C2F4; both reactions take place via a diradical intermediate. Dissociation of octafluoro-1-butene to the resonance stabilized perfluoroallyl radical is suggested to account for the favoring of simple bond rupture. These three reaction pathways were also observed in octafluoro-2-butene dissociation, however, the branching fraction is different than from octafluoro-1-butene. In octafluoro-2-butene all three channels occur with roughly equal probability. The reactions involving CF2 loss and C2F4 formation in octafluoro-2-butene are thought to proceed through the same diradical intermediate as in octafluoro-1-butene, necessitating a 1,2-fluorine migration.
- Longfellow, Cheryl A.,Berrie, Cindy L.,Suits, Arthur G.,Lee, Yuan T.
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p. 7202 - 7208
(2007/10/03)
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- IR Multiphoton Dissociation Dynamics of Octafluorocyclopentene: Time-Resolved Observation of Concerted Products :CF2 and Hexafluorobutadiene
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Real time observation of :CF2 and hexafluorobutadiene (HFBD) generated simultaneously in the concerted IR multiphoton dissociation of octafluorocyclopentene (OFCP) is reported.The formation rate of both the transients, i.e., hot HFBD and :CF2, which have an overlapping absorption at 250 nm, fits to a single exponential, with a rate constant (2.0 +/- 0.1) x 106s-1.The fast exponential decay of the transient signal up to 100 μs is assigned to electrocyclic isomerization of HFBD to hexafluorocyclobutene with a rate constant k = (5.7 +/- 0.2) x 104s-1, whereas the slower decay on the millisecond time scale suggests :CF2 dimerization to form C2F4, with a bimolecular rate constant (4.5 +/- 0.1) x 107M-1s-1.RRKM calculation for the unimolecular dissociation of OFCP and isomerization of HFBD gives an average energy of OFCP as 383 +/- 10kJ/mol and of nascent HFBD as 202 +/- 5 kJ/mol, corresponding to the experimental rates.The nascent vibrationally hot HFBD exhibits a red shift of 50 nm in the transient absorption spectrum.
- Chowdhury, P. K.
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p. 12084 - 12089
(2007/10/02)
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- Ionization Energies, Appearance Energies, and Thermochemistry of CF2O and FCO
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With the discharge flow-photoionization mass spectrometer (DF-PIMS) coupled to the U-11 beamline at the National Synchrotron Light Source, we have measured the ionization energies of C2F4, CF2, and CF2O and appearance energy of FCO+ from CF2O.The PIMS results corroborate those determined by other techniques.With high-level ab initio calculations that utilize a large basis set and isogyric corrections, we have determined an ionization energy of 9.3 +/- 0.1 eV for FCO.At 298 K, the heats of formation of FCO (-152 +/- 12 kJ/mol) and FCO+ (745.3 +/- 9.6 kJ/mol) fH0298(CF2O) = -607.9 +/- 7.1 kJ/mol> were determined and agree to within the uncertainties of other measurements but with much higher precision.We have evaluated the bond strengths D0298(F-CFO) and D0298(F-CO) to be 535 +/- 12 and 121 +/- 12 kJ/mol, respectively.
- Buckley, T. J.,Johnson, R. D.,Huie, R. E.,Zhang, Z.,Kuo, S.C.,Klemm, R. B.
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p. 4879 - 4885
(2007/10/02)
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- Small Rings, 83. - C3F2 Isomers: Generation by Pulsed Flash Pyrolysis and Matrix-Spectroscopic Identification
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Matrix-isolated difluorovinylidenecarbene (4) has been generated by pulsed flash pyrolysis from 1-chloro-3,3-difluorocyclopropene (8a) and 3,3-difluoro-1,2-diiodocyclopropene (8b).By subsequent photolysis 4 isomerizes to difluoropropargylene (5) and difluorocyclopropenylidene (6).The identification of the three new carbenes is based on the comparison of their experimental and calculated (MP2/6-31G*) infrared spectra. - Key Words: Matrix isolation / Photochemistry / Flash pyrolysis / Carbenes
- Maier, Guenther,Preiss, Thomas,Reisenauer, Hans Peter
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p. 779 - 782
(2007/10/02)
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- Gas-phase reactions of oxide and superoxide anions with CF4, CF3Cl, CF3Br, CF3I, and C2F4 at 298 and 500 K
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Rate constants and product branching fractions have been measured for the gas-phase reactions of oxide (O-) and superoxide (O2-) anions with the halocarbons CF4, CF3Cl, CF3Br, CF3I, and C2F4 using a variable temperature-selected ion flow tube (VT-SIFT) instrument operated at 298 and 500 K.The reactions of O- with CF3X (X = Cl, Br, I) are fast and produce F-, XF-, and XO- for all X.For CF3Cl and CF3Br, X- is also formed.For CF3I, CF3- and IOF- are minor products.O- reacts rapidly with C2F4 producing F- as the major ionic product, along with contributions from reactive detachment and minor formation of FCO-, CF3-, and C2F3O-.The reaction of O2- with CF3Cl is slow, and both clustering and X- formation were observed.For CF3Br and CF3I, the reactions with O2- are fast, and nondissociative charge transfer was observed in addition to X- formation.O2- reacts rapidly with C2F4 by reactive detachment, in addition to producing F- as the major ionic product with smaller amounts of F2-, FCO-, FCO2-, CF3O-, and C2F4O-.O- and O2- were both found to be unreactive with CF4 at 298 and 500 K.The efficiencies of the reactions of both O- and O2- with CF3X are greater for the heavier halides at both 298 and 500 K.The rate constants for the reactions of O2- with CF3X appear to correlate both with the rates of thermal electron attachment to CF3X and with the electron affinities of CF3X, indicating that the O2- + CF3X reaction mechanism may involve initial electron transfer followed by dissociation.Thus the negative electron affinity of CF3Cl may explain the very slow rate for reaction with O2- despite the available exothermic pathways.
- Morris, Robert A.
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p. 2372 - 2381
(2007/10/02)
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- Chemistry of CFn(1+) (n = 1-3) Ions with Halocarbons
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The gas-phase reactions of CF(1+), CF2(1+), and CF3(1+) with the halocarbons CF3Cl, CF3Br, CF3I, CF4, and C2F6 have been studied using a variable-temperature-selected ion flow tube (VT-SIFT) instrument at 300 and 496 K.The ion CF(1+) reacts rapidly with CF3X (X = Cl, Br, I) producing the ions CF2X(1+).In the reaction of CF(1+) with CF3Cl, CF3(1+) is also produced as a minor product.Curvature was observed in the pseudo-first-order kinetics plots for the reactions of CF(1+) with CF4 and C2F6.In both cases the curvature is attributed to the presence of two or more CF(1+) states (probably vibrational) of differing reactivities toward the perfluorocarbon of interest.This conclusion is supported by our observation of charge transfer from CF(1+) to NO, a reaction which is endothermic by 15 kJ/mol for the ground state of CF(1+).CF(1+) is unreactive with O2, N2, and Xe.The reactions of CF2(1+) with CF3X yield CF3(1+) and CF2X(1+) for X = Cl and Br; for X = I, CF2I(1+) and CF3I(1+) are produced.The overall reactions proceed at approximately the collision rate at 300 and 496 K, and the branching ratios are not strongly dependent on temperature.The reactions of CF2(1+) with CF4 and C2F6 produce CF3(1+) and C2F5(1+), respectively.The rate constants decrease significantly with increasing temperature.CF2(1+) reacts rapidly by charge transfer with NO.The reaction of CF2(1+) with O2, producing CF2O(1+), is inefficient.CF2(1+) is unreactive with N2.CF3(1+) reacts with CF3X (X = Cl, Br, I) at rates below the collision values, producing a single ionic product, CF2X(1+).While the rate constants for the reactions of CF3(1+) with CF3X increase in the series with increasing CF3X mass, the rate constants for reaction with each CF3X decrease sharply with increasing temperature.A mechanism is proposed in which the reaction proceeds on a double-well potential energy surface.No reaction was observed for the CF3(1+)/CF4 system.CF3(1+) appeared to react very slowly with C2F6 and NO, producing C2F5(1+) and NO(1+), respectively, but reactions with impurities in the neutral reagents cannot be ruled out as the source of these ions.CF3(1+) is unreactive with O2 and N2.
- Morris, Robert A.,Viggiano, A. A.,Doren, Jane M. Van,Paulson, John F.
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p. 2597 - 2603
(2007/10/02)
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- Infrared Multiphoton Decomposition of Hexafluorobenzene Investigated by Diode Laser Kinetic Spectroscopy: Detection of CF and CF2
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Infrared multiphoton decomposition of hexafluorobenzene (C6F6) was investigated by diode laser kinetic spectroscopy.Two transient species, CF and CF2, were detected, and the time evolution of their signals was observed.The signal of CF rose within 10 μs after a CO2 laser pulse and decreased with lifetime of about 200 μs, while that of CF2 rose slowly as CF decayed out.Final products observed by an FTIR spectrometer were mostly C2F4 and C6F5CF3.These experimental results suggested that CF was produced at the early stage of the reaction and that CF2 was produced by the reaction of CF with a certain fluorine-containing species and then decayedout through the dimerization and/or the reaction with C6F6.
- Sugawara, Ko-ichi,Watenabe, Akio,Koga, Yoshinori,Takeo, Harutoshi,Fukuda, Kenzo,et al.
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p. 3647 - 3649
(2007/10/02)
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- Infrared Laser Induced Multiphoton Dissociation of Decafluorocyclopentane in a Concerted Pathway: Time-Resolved Evidence of :CF2 Formation
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The infrared multiphoton dissociation (IRMPD) of decafluorocyclopentane (DFCP) generates tetrafluoroethylene and difluorocarbene as the primary products.The :CF2 dimerizes to form C2F4; the kinetics of the reaction is followed by monitoring the disappearance of :CF2 absorption at 249 nm in real time after the CO2 laser pulse, with a rate constant k2=4.35E7 M-1s-1.The vibrational temperature associated with the nascent :CF2 is found to be 1100 K.The MPD yield of DFCP shows a strong fluence dependence, with a threshold of ca. 0.5 J/cm2 for the 10 R(40) CO2 laser line.The MPD spectra reveal two peaks, one 22 cm-1 red-shifted from the 989 cm-1 strong IR absorption band.Addition of SF6 decreases the MPD yield.
- Chowdhury, P. K.,Rao, K. V. S. Rama,Mittal, J. P.
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p. 102 - 106
(2007/10/02)
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- Infrared Multiphoton-Induced Concerted :CF2 Elimination in Octafluorocyclopentene by a Pulsed CO2 Laser
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On infrared multiphoton excitation, octafluorocyclopentene (OFCP) undergoes a ring-opening reaction to give difluorocarbene and hexafluorobutadiene as unstable primary products which undergo further reactions; the former dimerizes to tetrafluoroethylene, and the latter isomerizes to its thermodynamically stable cyclic isomer.The multiphoton dissociation (MPD) yield of OFCP shows a strong fluence dependence, with a threshold of 0.3 J/cm2 for the 10R(32) line of the CO2 laser for inducing the reaction.Two characteristic peaks in the MPD spectra have been observed, both red-shifted from the ν20 ring deformation mode absorption peak of OFCP.Increase in pressure of OFCP or foreign gas addition has shown to deteriorate the MPD yield.
- Chowdhury, Pradyot K.,RAO, K. V. S. Rama,Mittal, J. P.
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p. 2877 - 2882
(2007/10/02)
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- Emission from FCO in the Reactions of Ozone with Fluoroethenes
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The gas-phase reactions of ozone with cis-1,2-difluoroethene, trans-1,2-difluoroethene, trifluoroethene, and chlorotrifluoroethene are all accompanied by light with a maximum intensity at approximately 425 nm.A partial vibrational analysis of this emission is presented and it is concluded that the emitting species is the FCO radical, as previously suggested.A comparison is made between the enthalpy changes of the primary reactions between ozone and the fluoroethenes and their correlation with the identity of the emitting species.The exothermicity of the reaction correlates with the chemiluminescent reaction channel.
- Toby, Sidney,Toby, Frina S.
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p. 4071 - 4073
(2007/10/02)
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- IR MATRIX ISOLATION SPECTRA OF SOME PERFLUORO ORGANIC FREE RADICALS PART III. n-C3F7 and iso-C3F7
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The perfluoro radicals n-C3F7 and iso-C3F7 have been prepared by pyrolyzing the corresponding iodides in a platinum effusion tube at temperatures between 450-550 deg C and isolated in argon matrices.By eliminating absorption bands attributed to known fluorine compounds and applying relative absorption band intensity correlations, several absorption bands have been assigned, some 30 to n-C3F7 and 29 to iso-C3F7, in the spectral range 2000-200 cm-1.A tentative vibrational assignment is presented for both species on the assumption of Cs symmetry.Some thermodynamic implications of the findings are also dicussed.
- Butler, R.,Snelson, A.
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