OH Radical Reaction Rate Coefficients, Infrared Spectrum, and Global Warming Potential of (CF3)2CFCH═CHF (HFO-1438ezy(E))

Oxidation pathways and kinetics of the 1,1,2,3-tetrafluoropropene (CF2CF-CH2F) reaction with Cl-atoms and subsequent aerial degradation of its product radicals in the presence of NO

To give a comprehensive account of the environmental acceptability of 1,1,2,3-tetrafluoropropene (CF2CF-CH2F) in the troposphere, we have examined the oxidation reaction pathways and kinetics of CF2CF-CH2F initiated by Cl-atoms using the second-order Møller-Plesset perturbation (MP2) theory along with the 6-31+G(d,p) basis set. We also performed single-point energy calculations to further refine the energies at the CCSD(T) level along with the basis sets 6-31+G(d,p) and 6-311++G(d,p). The estimation of the relative energies and thermodynamic parameters of the CF2CF-CH2F + Cl reaction clearly shows that Cl-atom addition reaction pathways are more dominant compared to H-abstraction reaction pathways. The value of the rate coefficient for each reaction channel is calculated using the conventional transition state theory (TST) over the temperature range of 200-1000 K at 1 atm. The estimated overall rate coefficients for the title reaction are found to be 1.10 × 10-12, 1.21 × 10-10, and 1.13 × 10-8 cm3 per molecule per s via the respective calculation methods viz. MP2/6-31+G(d,p), CCSD(T)//MP2/6-31+G(d,p), and CCSD(T)/6-311++G(d,p)//MP2/6-31+G(d,p), at 298.15 K. Moreover, the calculated rate coefficients and percentage branching ratio values suggest that the Cl-atom addition reaction at the β-carbon atom is more preferable to that of the α-carbon addition to CF2CF-CH2F. Based on the rate coefficient values calculated by the three different methods, the atmospheric lifetime for the title reaction at 298.15 K is estimated. The radiative efficiency (RE) and Global Warming Potential (GWP) results of the title molecule show that its GWP would be negligible. Further, we have explored the degradation of its product radicals in the presence of O2 and NO. From the degradation results, we have found that CF2(Cl)COF, FCOCH2F, FCFO and FCOCl are formed as stable end products along with various radicals such as ˙CF2Cl and ˙CH2F. Therefore, these findings of kinetic and mechanistic data can be applied to the development and implementation of a novel CFC replacement.

Hydrolysis of Formyl Fluoride Catalyzed by Sulfuric Acid and Formic Acid in the Atmosphere

Formyl fluoride (HFCO) is an important atmospheric molecule, and its reaction with the OH radical is an important pathway when degradation of HFCO is considered in earth's troposphere. Here, we study the hydrolysis of formyl fluoride (HFCO + H₂O) with sulfuric acid (H₂SO₄) and formic acid (HCOOH) acting as catalysts by utilizing M06-2X, CCSD(T)-F12a, and conventional transitional state theory with Eckart tunneling to explore the atmospheric impact of the above-said hydrolysis reactions. Our calculated results show that H₂SO₄ has a remarkably catalytic role in the gas-phase hydrolysis of HFCO, as the energy barriers of the HFCO + H₂O reaction are reduced from 39.22 and 41.19 to 0.26 and -0.63 kcal/mol with respect to the separate reactants, respectively. In addition, we also find that H₂SO₄ can significantly accelerate the decomposition of FCH(OH)₂ into hydrogen fluoride (HF) and HCOOH. This is because while the barrier height for the unimolecular decomposition of FCH(OH)₂ into HF and HCOOH is 31.63 kcal/mol, the barrier height for the FCH(OH)₂ + H₂SO₄ reaction is predicted to be -5.99 kcal/mol with respect to separate reactants. Nevertheless, the comparative relative rate analysis shows that the reaction between HFCO and the OH radical is still the most dominant pathway when the tropospheric degradation of HFCO is taken into account and that the gas-phase hydrolysis of HFCO may only occur with the help of H₂SO₄ when the atmospheric concentration of OH is about 10¹ molecules cm^-3 or less. Having an understanding from the present study that the gas-phase hydrolysis of HFCO in the presence of H₂SO₄ has very limited role possibly in the absence of sunlight, we also prefer here to emphasize that the HFCO + H₂O + H₂SO₄ reaction may occur on the surface of secondary organic aerosols for the formation of HCOOH.

Thermochemistry of Intermediates and Products in the Oxidation Reaction of 1,1,2-Trifluoroethene via OH Radical

Density functional theory (DFT) and composite ab initio based calculations are performed on trifluoroethane along with intermediate radicals, parent molecules of the radicals, and products related to the reaction of hydroxyl radical with 1,1,2-trifluoroethene, as a reference for hydrofluoroolefins (HFO). Potential energy barriers for internal rotations have been computed. Calculated torsional potentials are incorporated into the determination of entropy, S°₂₉₈, and heat capacities as a function of temperature, C_p(T), for each target molecule. Six isodesmic or isogyric reactions and five calculation methods are used to determine heats of formation at 298 K (Δ_fH₂₉₈) in kcal mol^-1 of each target species. The CBS-APNO method shows the best agreement with experimental data in comparisons from 16 reference reactions on Δ_rxnH of each method. The lowest configuration structures of each target species are reported. Intramolecular hydrogen bonds between the hydroxyl hydrogen atom and the fluorine atom on the adjacent carbon can stabilize molecules by up to 3 kcal mol^-1. R-OH bond dissociation energies are observed to increase with the number of fluorine atoms on the carbon connected to hydroxy group. Recommended Δ_fH₂₉₈ values in kcal mol^-1 derived from the most stable conformers are CF₂(OH)CH₂F (-213.0), CF₂(O^•)CH₂F (-148.6), CF₂(OH)C^•FH (-162.4), CHF₂CHFOH (-207.5), CHF₂C^•FOH (-158.3), C^•F₂CHFOH (-155.5), CHF₂CHFO^• (-150.4), CF₃CH₂OH (-212.5), and CF₃C^•HOH (-167.9).

Rate Coefficient Measurements and Theoretical Analysis of the OH + ( E)-CF3CH═CHCF3 Reaction

Rate coefficients, k, for the gas-phase reaction of the OH radical with ( E)-CF₃CH═CHCF₃ (( E)-1,1,1,4,4,4-hexafluoro-2-butene, HFO-1336mzz(E)) were measured over a range of temperatures (211-374 K) and bath gas pressures (20-300 Torr; He, N₂) using a pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) technique. k₁( T) was independent of pressure over this range of conditions with k₁(296 K) = (1.31 ± 0.15) × 10^-13 cm³ molecule^-1 s^-1 and k₁( T) = (6.94 ± 0.80) × 10^-13exp[-(496 ± 10)/ T] cm³ molecule^-1 s^-1, where the uncertainties are 2σ, and the pre-exponential term includes estimated systematic error. Rate coefficients for the OD reaction were also determined over a range of temperatures (262-374 K) at 100 Torr (He). The OD rate coefficients were ∼15% greater than the OH values and showed similar temperature dependent behavior with k₂( T) = (7.52 ± 0.44) × 10^-13exp[-(476 ± 20)/ T] and k₂(296 K) = (1.53 ± 0.15) × 10^-13 cm³ molecule^-1 s^-1. The rate coefficients for reaction 1 were also measured using a relative rate technique between 296 and 375 K with k₁(296 K) measured to be (1.22 ± 0.1) × 10^-13 cm³ molecule^-1 s^-1, in agreement with the PLP-LIF results. In addition, the 296 K rate coefficient for the O₃ + ( E)-CF₃CH═CHCF₃ reaction was determined to be <5.2 × 10^-22 cm³ molecule^-1 s^-1. A theoretical computational analysis is presented to interpret the observed positive temperature dependence for the addition reaction and the significant decrease in OH reactivity compared to the ( Z)-CF₃CH═CHCF₃ stereoisomer reaction. The estimated atmospheric lifetime of ( E)-CF₃CH═CHCF₃, due to loss by reaction with OH, is estimated to be ∼90 days, while the actual lifetime will depend on the location and season of its emission. Infrared absorption spectra of ( E)-CF₃CH═CHCF₃ were measured and used to estimate the 100 year time horizon global warming potentials (GWP) of 32 (atmospherically well-mixed) and 14 (lifetime-adjusted).

Atmospheric chemistry of Z- and E-CF3CHCHCF3

The first determination of the atmospheric chemistry of E-CF₃CHCHCF₃ and of the Cl and O₃ initiated atmospheric chemistry of Z-CF₃CHCHCF₃.