Reaction of CF3 radicals with CO and O2. Isolation of bis(trifluoromethyl)peroxydicarbonate,CF3OC(O)OOC(O)OCF3, and identification of bis(trifluoromethyl)trioxydicarbonate,CF3OC(O)OOOC(O)OCF3

The synthesis of CF3OC(O)OOCF3, CF3OC(O)OOC(O)OCF3, and CF3OC(O)OOOC(O)OCF3 is accomplished by the photolysis of a mixture of (CF3CO)2O, CO, and O2. Pure CF3OC(O)OOCF3 and CF3OC(O)OOC(O)OCF3 are isolated after thermal decomposition of CF3OC(O)OOOC(O)OCF3 and repeated trap-to-trap condensation. Additional spectroscopic data of known CF3OC(O)OOCF3 are obtained by recording NMR, IR, Raman, and UV spectra: At room temperature CF3OC(O)OOC(O)OCF3 is stable for days in the liquid or gaseous state. The melting point is -38 degrees C, and the boiling point is extrapolated to 73 degrees C from the vapor pressure curve log p = 8.657-1958/T (p/mbar, T/K). The new compound is characterized by molecular mass determination and by NMR, vibrational, and UV spectroscopy. The new trioxide CF3OC(O)OOOC(O)OCF3 cannot be separated from CF3-OC(O)OOC(O)OCF3 by distillation due to their similar boiling points. CF3OC(O)OOOC(O)OCF3 decomposes at room temperature within hours into a mixture of CF3OC(O)OOC(O)OCF3, CF3OC(O)OOCF3, CO2, and O2. Its characterization is discussed along with a possible mechanism for formation and decomposition reactions.     

The open-chain trioxide CF3OC(O)OOOC(O)OCF3

The open-chain trioxide CF(3)OC(O)OOOC(O)OCF(3) is synthesised by a photochemical reaction of CF(3)C(O)OC(O)CF(3), CO and O(2) under a low-pressure mercury lamp at -40 degrees C. The isolated trioxide is a colourless solid at -40 degrees C and is characterised by IR, Raman, UV and NMR spectroscopy. The compound is thermally stable up to -30 degrees C and decomposes with a half-life of 1 min at room temperature. Between -15 and +14 degrees C the activation energy for the dissociation is 86.5 kJ mol(-1) (20.7 kcal mol(-1)). Quantum chemical calculations have been performed to support the vibrational assignment and to discuss the existence of rotamers.     

Atmospheric chemistry of CF3OCF2CF2H and CF3OC(CF3)2H: reaction with Cl atoms and OH radicals, degradation mechanism, global warming potentials, and empirical relationship between k(OH) and k(Cl) for organic compounds

Using FTIR smog chamber techniques, k(Cl + CF3OCF2CF2H) = (2.70 +/- 0.52) x 10(-16), k(OH + CF3OCF2CF2H) = (2.26 +/- 0.18) x 10(-15), k(Cl + CF3OC(CF3)2H) = (1.58 +/- 0.27) x 10(-18) and k(OH + CF3OC(CF3)2H) = (3.26 +/- 0.95) x 10(-16) cm3 molecule(-1) s(-1) were measured. The atmospheric lifetimes of CF3OCF2CF2H and CF3OC(CF3)2H are estimated to be 27 and 216 years, respectively. Chlorine atom initiated oxidation of CF3OCF2CF2H in 700 Torr of air in the presence of NO(x) gives CF3OC(O)F in a molar yield of 36 +/- 5% and COF2 in a molar yield of 174 +/- 9%, whereas oxidation of CF3OC(CF3)2H gives CF3OC(O)CF3 and COF2 in molar yields that are indistinguishable from 100%. Quantitative infrared spectra were recorded and used to estimate global warming potentials of 3690 and 8230 (100 year time horizon, relative to CO2) for CF3OCF2CF2H and CF3OC(CF3)2H, respectively. All experiments were performed in 700 Torr of N2/O2 diluent at 296 +/- 2 K. An empirical relationship can be used to estimate the preexponential factor, which can be combined with k(298 K) to give the temperature dependence of reactions of OH radicals with organic compounds proceeding via H-atom abstraction: log(A/n) = (0.239 +/- 0.027) log(k(OH)/n) - (8.69 +/- 0.372), k(OH) is the rate constant at 298 K and n is the number of H atoms. The rates of H-atom abstraction by OH radicals and Cl atoms at 298 K from organic compounds are related by the expression log(k(OH)) = (0.412 +/- 0.049) log(k(Cl)) - (8.16 +/- 0.72). The utility of these expressions and the atmospheric chemistry of the title hydrofluoroethers are discussed.     

Synthesis and characterization of trifluoromethyl fluoroformyl peroxycarbonate,CF3OC(O)OOC(O)F

The synthesis of CF(3)OC(O)OOC(O)F is accomplished by the photolysis of a mixture of (CF(3)CO)(2)O, FC(O)C(O)F, CO, and O(2) at -15 degrees C using a low-pressure mercury lamp. The new peroxide is obtained in pure form in low yield after repeated trap-to-trap condensation and is characterized by NMR, IR, Raman, and UV spectroscopy. Geometrical parameters were studied by ab initio methods [B3LYP/6-311+G(d)]. At room temperature, CF(3)OC(O)OOC(O)F is stable for many days in the liquid or gaseous state. The melting point is -87 degrees C, and the boiling point is extrapolated to 45 degrees C from the vapor pressure curve log p = 8.384 - 1715/T (p/mbar, T/K). A possible mechanism for the formation of CF(3)OC(O)OOC(O)F is discussed, and its properties are compared with those of related compounds.     

The trifluoromethoxycarbonyl radical CF(3)OCO

The trifluoromethoxycarbonyl radical CF(3)OCO is formed by low-pressure flash pyrolysis of CF(3)OC(O)OOC(O)OCF(3) or CF(3)OC(O)OOCF(3) in the presence of a high excess of CO and subsequent quenching of the reaction mixture as a CO matrix. The IR and UV spectra are recorded, and a DFT study of CF(3)OCO is presented. According to the quantum chemical calculations, two rotamers should exist with an energy difference between the isomers equal or larger than 12 kJmol(-1). By comparing calculated and observed IR spectra, the presence of the trans form of the CF(3)OCO radical is identified in the matrix. The reaction of CF(3)O radicals with CO leading to CF(3)OCO is calculated to be exothermic by 33.6 kJmol(-1). CF(3)OCO dissociates when irradiated by UV light with lambda<370 nm into CF(3) radicals and CO(2). Experiments show that CF(3) radicals do not react with solid CO to give CF(3)CO.     

Perfluoromethyl fluorocarbonyl peroxide,CF3OOC(O)F: structure,conformations, and vibrational spectra studied by experimental and theoretical methods

The conformational properties and the geometric structure of perfluoromethyl fluorocarbonyl peroxide, CF(3)OOC(O)F, have been studied by matrix IR spectroscopy, gas electron diffraction, and quantum chemical calculations (HF, B3LYP, and MP2 methods with 6-311G* basis sets). Matrix IR spectra imply a mixture of syn and anti conformers (orientation of the C=O bond relative to the O-O bond) with DeltaH degrees = H(anti) degrees - H(syn) degrees = 2.16(22) kcal/mol. At room temperature, the contribution of the anti rotamer is about 3.0%. The O-O bond (1.422(15) A) is within the experimental uncertainties equal to those in related symmetrically substituted peroxides CF(3)OOCF(3) and FC(O)OOC(O)F (1.419(20) and 1.419(9) A, respectively), and the dihedral angle delta(COOC) (111(5) degrees ) is intermediate between the values in these two compounds (123(4) degrees and 83.5(14) degrees, respectively).     

Bis(trifluoroacetyl) peroxide, CF(3)C(O)OOC(O)CF(3)

Pure, highly explosive CF(3)C(O)OOC(O)CF(3) is prepared for the first time by low-temperature reaction between CF(3)C(O)Cl and Na(2)O(2). At room temperature CF(3)C(O)OOC(O)CF(3) is stable for days in the liquid or gaseous state. The melting point is -37.5 degrees C, and the boiling point is extrapolated to 44 degrees C from the vapor pressure curve log p = -1875/T + 8.92 (p/mbar, T/K). Above room temperature the first-order unimolecular decay into C(2)F(6) + CO(2) occurs with an activation energy of 129 kJ mol(-1). CF(3)C(O)OOC(O)CF(3) is a clean source for CF(3) radicals as demonstrated by matrix-isolation experiments. The pure compound is characterized by NMR, vibrational, and UV spectroscopy. The geometric structure is determined by gas electron diffraction and quantum chemical calculations (HF, B3PW91, B3LYP, and MP2 with 6-31G basis sets). The molecule possesses syn-syn conformation (both C=O bonds synperiplanar to the O-O bond) with O-O = 1.426(10) A and dihedral angle phi(C-O-O-C) = 86.5(32) degrees. The density functional calculations reproduce the experimental structure very well.     

Kinetics and mechanisms of CF3CHFOCH3, CF3CHFOC(O)H, and FC(O)OCH3 reactions with OH radicals

The kinetics and mechanism of oxidation of CF3CHFOCH3 was studied using an 11.5-dm3 environmental reaction chamber. OH radicals were produced by UV photolysis of an O3-H2O-He mixture at an initial pressure of 200 Torr in the chamber. The rate constant of the reaction of CF3CHFOCH3 with OH radicals (k1) was determined to be (1.77 +/- 0.69) x 10(-12) exp[(-720 +/- 110)/T] cm3 molecule(-1)(s-1) by means of a relative rate method at 253-328 K. The mechanism of the reaction was investigated by FT-IR spectroscopy at 298 K. CF3CHFOC(O)H, FC(O)OCH3, and COF2 were determined to be the major products. The branching ratio (k1a/k1b) for the reactions CF3CHFOCH3 + OH --> CF3CHFOCH2* + H2O (k1a) and CF3CHFOCH3 + OH --> CF3CF*OCH3 + H2O (k1b) was estimated to be 4.2:1 at 298 K from the yields of CF3CHFOC(O)H, FC(O)OCH3, and COF2. The rate constants of the reactions of CF3CHFOC(O)H (k2) and FC(O)OCH3 (k3) with OH radicals were determined to be (9.14 +/- 2.78) x 10(-13) exp[(-1190 +/- 90)/T] and (2.10 +/- 0.65) x 10(-13) exp[(-630 +/- 90)/T] cm3 molecule(-1)(s-1), respectively, by means of a relative rate method at 253-328 K. The rate constants at 298 K were as follows: k1 = (1.56 +/- 0.06) x 10-13, k2 = (1.67 +/- 0.05) x 10-14, and k3 = (2.53 +/- 0.07) x 10-14 cm3 molecule(-1)(s-1). The tropospheric lifetimes of CF3CHFOCH3, CF3CHFOC(O)H, and FC(O)OCH3 with respect to reaction with OH radicals were estimated to be 0.29, 3.2, and 1.8 years, respectively.     

A systematic investigation into the mechanism of the reaction between CF3 radicals and CO/O2

A complete study of the reaction of CF(3) radicals in the presence of CO and O(2) was carried out by using isotopically labeled reagents to form, selectively, all the possible isotopomers of the intermediate trioxide, CF(3)OC(O)OOOC(O)OCF(3), and of the stable peroxide, CF(3)OC(O)OOC(O)OCF(3). Analyses were carried out by means of FTIR spectroscopy in combination with ab initio calculations. At temperatures close to 0 degrees C, the acyloxy radicals formed were shown to exist long enough to yield a statistical mixture of isotopomers. In previous reports their lifetime was considered to be too short.     

The trifluoromethoxy carbonyl peroxy radical CF3OC(O)OO

CF3OC(O)OO radicals are generated by low-pressure flash thermolysis of CF3OC(O)OOOC(O)OCF3 highly diluted in inert gases and followed by subsequent isolation in an inert-gas matrix at low temperatures. The by-products CO2, COF2, CF3O, and CF3OO are detected. The new peroxy radical is characterized by IR and UV spectroscopy and by its UV photolytic decay which leads to the formation of CF3OO and CO2. According to DFT calculations the exitence of three stable rotamers is predicted and two of them are found experimentally.     

Preparation and conformational properties of the perfluoro diether CF(3)OCF(2)OCF(2)C(O)F, a model molecule to study properties of perfluoro polyethers

The compound CF(3)OCF(2)OCF(2)C(O)F was prepared by oxidation of hexafluoropropene with molecular oxygen in the gas-phase using CF(3)OF as initiator. (13)C NMR, FTIR, Raman, UV-vis, and mass spectra were obtained and interpreted. The theoretical structure studies were performed by the calculation of the potential energy surfaces, using the results obtained for a smaller related molecule, CF(3)OCF(2)C(O)F, as a starting point. A high degree of conformational flexibility of this compound is evidenced by the values of several conformations, varying within the range of 1 kcal/mol. Theoretical calculations predict chain conformations as the most stable molecular forms, as expected from the presence of the anomeric effect. The experimental fundamental vibrational modes are compared with those obtained theoretically, using ab initio and density functional theory methods, HF/6-31+G and B3LYP/6-31+G, respectively. The density of the compound at ambient temperature (delta = 1.7(1) g/mL), its melting point (mp = -140(5) degrees C), its boiling point (bp = 14.5 (1) degrees C), and the relation between its vapor pressure and the absolute temperature (ln P = 13.699 - 2023.4/T) were also determined.     

Use of gas-phase (1)H NMR to determine the kinetics of unimolecular rearrangement of 2,2-dichloro-1-methylenecyclopropane and the bimolecular dimerization of (dichloromethylene)cyclopropane

Gas-phase (1)H NMR analysis has been applied to investigate the kinetics of the unimolecular rearrangement of 2,2-dichloro-1-methylenecyclopropane (1) to (dichloromethylene)cyclopropane (2) [k(1) = 7.9 x 10(12) exp(-34.4 +/- 0.6 kcal mol(-1)/RT)], as well as for the subsequent second-order dimerization of 2 [k(2) = 2.4 x 10(6) exp(-18.5 +/- 1.1 kcal mol(-1)/RT)] to form 7,7,8,8-tetrachlorodispiro[2.0.2.2]octane (3)     

Thermochemical parameters of CHFO and CF2O

Thermochemical properties of CHFO and CF 2O and their derivatives were calculated by using coupled-cluster theory (U)CCSD(T) calculations with the aug-cc-pV nZ ( n = D, T, Q, 5) basis sets extrapolated to the complete basis set limit with additional corrections. The predicted properties include the following. Enthalpies of formation (298 K, kcal/mol): Delta H f (CF 2O) = -144.7, Delta H f(CHFO) = -91.1, Delta H f (CFO (*)) = -41.6. Bond dissociation energy (0 K, kcal/mol): BDE(CFO-F) = 120.7, BDE(CHO-F) = 119.1, BDE(CFO-H) = 100.2. Ionization potential (eV): IP 1(CF 2O) = 13.04, IP 2(CF 2O) = 14.09, IP 1(CHFO) = 12.41, IP 2(CHFO) = 13.99, IP 1(CFO (*)) = 9.34. Proton affinity (298 K, kcal/mol), PA O(CF 2O) = 148.8, PA O(CHFO) = 156.7, PA F(CHFO) = 154.5 kcal/mol. Electron affinity: EA(CFO (*)) = 2.38 eV. Triplet-singlet separation gap (eV): Delta E T1-S0(CF 2O) = 4.47, Delta E T1-S0(CHFO) = 4.36. Triplet-triplet transition energy (eV): Delta E T2-T1(CF 2O) = 0.44. The new calculated values contribute to solving some persistent discrepancies in the literature. The effects of F-atoms on thermochemical parameters are not linearly additive, and the changes are largely dominated by the first F-substitution. On the basis of the calculated proton affinities of CF 2O and CF 3OH, the nucleophilicities of the oxygen atoms are, within computational errors, the same in both compounds.     

Trifluoromethoxycarbonyl peroxynitrate, CF3OCOOONO2

The trioxide, CF(3)OC(O)OOOC(O)OCF(3), reacts with NO(2) at 0 degrees C to yield the new peroxynitrate, CF(3)OC(O)OONO(2), which is stable for hours at room temperature. It is spectroscopically characterized and some thermal properties are reported. From the vapor pressure, ln(p/p(0)) = 14.06 - 4565/T, of the liquid above the melting point of -89 degrees C, the extrapolated boiling point is 52 degrees C. CF(3)OC(O)OONO(2) dissociates at higher temperatures and low pressures into the radicals CF(3)OC(O)OO and NO(2) as demonstrated by matrix isolation experiments. The matrix-isolated peroxy radicals consist in a rotameric mixture of trans,trans,trans-CF(3)OC(O)OO and trans,trans,cis-CF(3)OC(O)OO, where trans and cis denote dihedral angles of ca. 180 degrees and 0 degree, respectively, around beta F-C-O-C, beta C-O-C-O, and beta O-C-O-O, with an equilibrium composition dependent on the thermolysis temperature. The radical trans,trans,cis-CF(3)OC(O)OO is found to be ca. 3 kJ mol(-1) higher in enthalpy than trans,trans,trans-CF(3)OC(O)OO. DFT calculations are performed to support the vibrational assignments and to provide structural information about CF(3)OC(O)OONO(2).     

CF3CF=CH2 and (Z)-CF3CF=CHF: temperature dependent OH rate coefficients and global warming potentials

Rate coefficients over the temperature range 206-380 K are reported for the gas-phase reaction of OH radicals with 2,3,3,3-tetrafluoropropene (CF(3)CF=CH(2)), k(1)(T), and 1,2,3,3,3-pentafluoropropene ((Z)-CF(3)CF=CHF), k(2)(T), which are major components in proposed substitutes for HFC-134a (CF(3)CFH(2)) in mobile air-conditioning units. Rate coefficients were measured under pseudo-first-order conditions in OH using pulsed-laser photolysis to produce OH and laser-induced fluorescence to detect it. Rate coefficients were found to be independent of pressure between 25 and 600 Torr (He, N(2)). For CF(3)CF=CH(2), the rate coefficients, within the measurement uncertainty, are given by the Arrhenius expression k(1)(T)=(1.26+/-0.11) x 10(-12) exp[(-35+/-10)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K)=(1.12+/-0.09) x 10(-12) cm(3) molecule(-1) s(-1). For (Z)-CF(3)CF=CHF, the rate coefficients are given by the non-Arrhenius expression k(2)(T)=(1.6+/-0.2) x 10(-18)T(2) exp[(655+/-50)/T] cm(3) molecule(-1) s(-1) where k(2)(296 K)=(1.29+/-0.06) x 10(-12) cm(3) molecule(-1) s(-1). Over the temperature range most relevant to the atmosphere, 200-300 K, the Arrhenius expression k(2)(T)=(7.30+/-0.7) x 10(-13) exp[(165+/-20)/T] cm(3) molecule(-1) s(-1) reproduces the measured rate coefficients very well and can be used in atmospheric model calculations. The quoted uncertainties in the rate coefficients are 2sigma (95% confidence interval) and include estimated systematic errors. The global warming potentials for CF(3)CF=CH(2) and (Z)-CF(3)CF=CHF were calculated to be <4.4 and <3.6, respectively, for the 100 year time horizon using infrared absorption cross sections measured in this work, and atmospheric lifetimes of 12 and 10 days that are based solely on OH reactive loss.     

Rate coefficients and equilibrium constant for the CH2CHO + O2 reaction system

The kinetics of the CH2CHO + O2 reaction was experimentally studied in two quasi-static reactors and a discharge flow-reactor at temperatures ranging from 298 to 660 K and pressures between 1 mbar and 46 bar with helium as the bath gas. The CH2CHO radicals were produced by the laser-flash photolysis of ethyl vinyl ether at 193 nm and by the reaction F + CH3CHO, respectively. Laser-induced fluorescence excited at 337 or 347.4 nm was used to monitor the CH2CHO concentration. The reaction proceeded via reversible complex formation with subsequent isomerization and fast decomposition: CH2CHO + O2 <= => O2CH2CHO --> HO2CH2CO --> products. The rate coefficients for the first and second steps were determined (k1, k-1, k2) and analyzed by a master equation with specific rate coefficients from the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Molecular and transition-state parameters were obtained from quantum chemical calculations. A third-law analysis led to the following thermodynamic parameters for the first step: Delta(R)S degrees 300K(1) = -144 J K(-1) mol(-1) (1 bar) and Delta(R)H degrees 300K(1) = (-101 +/- 4) kJ mol(-1). From the falloff analysis, the following temperature dependencies for the low- and high-pressure limiting rate coefficients were obtained: k1(0) = 5.14 x 10(-14) exp(210 K/T) cm(-3) s(-1); k1(infinity) = 1.7 x 10(-12) exp(-520 K/T) cm(-3) s(-1); and k2(infinity) = 1.3 x 10(12) exp[-(82 +/- 4) kJ mol(-1)/RT] s(-1). Readily applicable analytical representations for the pressure and temperature dependence of k1 were derived to be used in kinetic modeling.     

The reaction of Li[Al(OR)4] R = OC(CF3)2Ph, OC(CF3)3 with NO/NO2 giving NO[Al(OR)4], Li[NO3] and N2O. The synthesis of NO[Al(OR)4] from Li[Al(OR)4] and NO[SbF6] in sulfur dioxide solution

NO[Al(OC(CF(3))(2)Ph)(4)] 1 and NO[Al(OC(CF(3))(3))(4)] 2 were obtained by the metathesis reaction of NO[SbF(6)] and the corresponding Li[Al(OR)(4)] salts in liquid sulfur dioxide solution in ca 40% (1) and 85% (2) isolated yield. 1 and 2, as well as Li[NO(3)] and N(2)O, were also given by the reaction of an excess of mixture of (90 mol%) NO, (10 mol%) NO(2) with Li[Al(OR)(4)] followed by extraction with SO(2). The unfavourable disproportionation reaction of 2NO(2)(g) to [NO](+)(g) and [NO(3)](-)(g)[DeltaH degrees = +616.2 kJ mol(-1)] is more than compensated by the disproportionation energy of 3NO(g) to N(2)O(g) and NO(2)(g)[DeltaH degrees =-155.4 kJ mol(-1)] and the lattice energy of Li[NO(3)](s)[U(POT)= 862 kJ mol(-1)]. Evidence is presented that the reaction proceeds via a complex of [Li](+) with NO, NO(2)(or their dimers) and N(2)O. NO(2) and Li[Al(OC(CF(3))(3))(4)] gave [NO(3)(NO)(3)][Al(OC(CF(3))(3))(4)](2), NO[Al(OC(CF(3))(3))(4)] and (NO(2))[Al(OC(CF(3))(3))(4)] products. The aluminium complex [Li[AlF(OC(CF(3))(2)Ph)(3)]](2) 3 was prepared by the thermal decomposition of Li[Al(OC(CF(3))(2)Ph)(4)]. Compounds 1 and 3 were characterized by single crystal X-ray structural analyses, 1-3 by elemental analyses, NMR, IR, Raman and mass spectra. Solid 1 contains [Al(OC(CF(3))(2)Ph)(4)](-) and [NO](+) weakly linked via donor acceptor interactions, while in the SO(2) solution there is an equilibrium between the associated [NO](+)[Al(OC(CF(3))(2)Ph)(4)](-) and separated solvated ions. Solid 2 contains essentially ionic [NO](+) and [Al(OC(CF(3))(3))(4)](-). Complex 3 consists of two [Li[AlF(OC(CF(3))(2)Ph)(3)]] units linked via fluorine lithium contacts. Compound 1 is unstable in the SO(2) solution and decomposes to yield [AlF(OC(CF(3))(2)Ph)(3)](-), [(PhC(CF(3))(2)O)(3)Al(mu-F)Al(OC(CF(3))(2)Ph)(3)](-) anions as well as (NO)C(6)H(4)C(CF(3))(2)OH, while compound 2 is stable in liquid SO(2). The [small nu](NO(+)) in 1 and [NO](+)(toluene)[SbCl(6)] are similar, implying similar basicities of [Al(OC(CF(3))(2)Ph)(4)](-) and toluene.     

Reflected shock tube and theoretical studies of high-temperature rate constants for OH+CF3H<-->CF3+H2O and CF3+OH-->products

The reflected shock tube technique with multipass absorption spectrometric detection of OH radicals at 308 nm, using either 36 or 60 optical passes corresponding to total path lengths of 3.25 or 5.25 m, respectively, has been used to study the bimolecular reactions, OH+CF3H-->CF3+H2O (1) and CF3+H2O-->OH+CF3H (-1), between 995 and 1663 K. During the course of the study, estimates of rate constants for CF3+OH-->products (2) could also be determined. Experiments on reaction -1 were transformed through equilibrium constants to k1, giving the Arrhenius expression k1=(9.7+/-2.1)x10(-12) exp(-4398+/-275K/T) cm3 molecule(-1) s(-1). Over the temperature range, 1318-1663 K, the results for reaction 2 were constant at k2=(1.5+/-0.4)x10(-11) cm3 molecule(-1) s(-1). Reactions 1 and -1 were also studied with variational transition state theory (VTST) employing QCISD(T) properties for the transition state. These a priori VTST predictions were in good agreement with the present experimental results but were too low at the lower temperatures of earlier experiments, suggesting that either the barrier height was overestimated by about 1.3 kcal/mol or that the effect of tunneling was greatly underestimated. The present experimental results have been combined with the most accurate earlier studies to derive an evaluation over the extended temperature range of 252-1663 K. The three parameter expression k1=2.08x10(-17) T1.5513 exp(-1848 K/T) cm3 molecule(-1) s(-1) describes the rate behavior over this temperature range. Alternatively, the expression k1,th=1.78x10(-23) T3.406 exp(-837 K/T) cm3 molecule(-1) s(-1) obtained from empirically adjusted VTST calculations over the 250-2250 K range agrees with the experimental evaluation to within a factor of 1.6. Reaction 2 was also studied with direct CASPT2 variable reaction coordinate transition state theory. The resulting predictions for the capture rate are found to be in good agreement with the mean of the experimental results and can be represented by the expression k2,th=2.42x10(-11) T-0.0650 exp(134 K/T) cm3 molecule(-1) s(-1) over the 200-2500 K temperature range. The products of this reaction are predicted to be CF2O+HF.     

Appearance potential of CF3+ in the dissociative photoionization of CF3Br

Measurements of the appearance potential for the production of CF3+ in the photoionization of CF3Br are in sharp disagreement, contributing to controversy in the heat of formation of CF3+. We reexamine our previous work and add additional experiments, obtaining AP(CF3+/CF3Br) = 11.64 +/- 0.04 eV as the average of four measurements made under widely different conditions. This is higher by 0.08 eV than the value we reported previously. Our new value for Delta(f)H0 degrees (CF3+) is now 88.0 +/- 0.9 kcal mol(-1). We compare our method with other techniques.     

Rate coefficients for the reactions of OH with CF3CH2CH3 (HFC-263fb), CF3CHFCH2F (HFC-245eb), and CHF2CHFCHF2 (HFC-245ea) between 238 and 375 K

Rate coefficients for reaction of the hydroxyl radical (OH) with three hydrofluorocarbons (HFCs) CF3CH2CH3, HFC-263fb, (k1); CF3CHFCH2F, HFC-245eb, (k2); and CHF2CHFCHF2, HFC-245ea, (k3); which are suggested as potential substitutes to chlorofluorocarbons (CFCs), were measured using pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) between 235 and 375 K. The Arrhenius expressions obtained are k1(T) = (4.36 +/- 0.72) x 10(-12) exp[-(1290 +/- 40)/T] cm3 molecule(-1) s(-1); k2(T) = (1.23 +/- 0.18) x 10(-12) exp[-(1250 +/- 40)/T] cm3 molecule(-1) s(-1); k3(T) = (1.91 +/- 0.42) x 10(-12) exp[-(1375 +/- 100)/T] cm3 molecule(-1) s(-1). The quoted uncertainties are 95% confidence limits and include estimated systematic errors. The present results are discussed and compared with rate coefficients available in the literature. Our results are also compared with those calculated using structure activity relationships (SAR) for fluorinated compounds. The IR absorption cross-sections at room temperature for these compounds were measured over the range of 500 to 4000 cm-1. The global warming potentials (GWPs) of CF3CH2CH3(HFC-263fb), CF3CHFCH2F(HFC-245eb), and CHF2CHFCHF2(HFC-245ea) were calculated to be 234, 962, and 723 for a 20-year horizon; 70, 286, and 215 for a 100-year horizon; and 22, 89, and 68 for a 500-year horizon; and the atmospheric lifetimes of these compounds are 0.8, 2.5, and 2.6 years, respectively. It is concluded that these compounds are acceptable substitutes for CFCs in terms of their impact on Earth's climate.