F:Flammable;2154-59-8Relevant academic research and scientific papers
Ultrafast absorption spectroscopy of photodissociated CF2Br2: Details of the reaction mechanism and evidence for anomalously slow intramolecular vibrational redistribution within the CF2Br intermediate
Gosnell, T. R.,Taylor, A. J.,Lyman, J. L.
, p. 5949 - 5953 (1991)
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.
Photodissociation dynamics of the reaction CF2Br2 + hv → CF2 + 2Br. Energetics, threshold and nascent CF2 energy distributions for λ = 223-260 nm
Cameron, Melanie R.,Johns, Stephen A.,Metha, Gregory F.,Kable, Scott H.
, p. 2539 - 2547 (2000)
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.
Reaction of Trifluoromethyl Iodide on Ni(100)
Myli, K. B.,Grassian, V. H.
, p. 1498 - 1504 (1995)
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).
Competition between unimolecular C-Br-bond fission and Br2 elimination in vibrationally highly excited CF2Br2
Abel, B.,Hippler, H.,Lange, N.,Schuppe, J.,Troe, J.
, p. 9681 - 9690 (1994)
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.
Halomethylenes: Effects of Halogen Substitution on Absolute Heats of Formation
Lias, Sharon G.,Karpas, Zeev,Liebman, Joel F.
, p. 6089 - 6096 (1985)
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.
The kinetics of the CF3 + CF3 and CF3 + F combination reactions at 290 K and at He-pressures of ≈ 1-6 Torr
Dils, Bart,Vertommen, Johan,Carl, Shaun Avondale,Vereecken, Luc,Peeters, Jozef
, p. 1187 - 1193 (2005)
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.
Shock wave studies of the pyrolysis of fluorocarbon oxygenates. II. the thermal dissociation of C4F8O
Cobos,Hintzer,S?lter,Tellbach,Thaler,Troe
, p. 3159 - 3164 (2017/08/17)
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.
Shock wave studies of the pyrolysis of fluorocarbon oxygenates. I. The thermal dissociation of C3F6O and CF3COF
Cobos,Hintzer,S?lter,Tellbach,Thaler,Troe
, p. 3151 - 3158 (2017/08/17)
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.
Difluorocarbene studied with threshold photoelectron spectroscopy (TPES): Measurement of the first adiabatic ionization energy (AIE) of CF2
Innocenti, Fabrizio,Eypper, Marie,Lee, Edmond P. F.,Stranges, Stefano,Mok, Daniel K. W.,Chau, Foo-Tim,King, George C.,Dyke, John M.
experimental part, p. 11452 - 11460 (2009/12/03)
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).
Rate measurement of the reaction of CF2Cl radicals with O 2
Codnia, Jorge,Azcarate, Maria Laura
, p. 755 - 762 (2008/02/11)
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.
