Quantum mechanical studies on the singlet and triplet potential energy surface of the reactions CF3O2 + I,CF3O + OI and CF3 + OIO

The singlet and triplet potential energy surfaces for the reactions CF₃O₂ + I (1), CF₃O + OI (2) and CF₃ + OIO (3) are investigated using ab initio quantum mechanical methods. Four important isomeric energy minima were found, three on the singlet surface, CF₃OOI, CF₃OIO and CF₃IO₂ and one on the triplet surface ³CF₃OIO. CF₂O + FOI are shown to be the most probable products for all reactions, CF₃O +I and CF₃O + O(³P) are possible for reactions (2) and (3) while the reaction pathway leading to CF₃O +OI is also possible for reaction (3).     

Theoretical investigation on kinetics and thermochemistry of reaction of CHF2CF2OCH2CF3 with OH radicals and global warming potentials

Theoretical investigation has been carried out on the mechanism, kinetics and thermochemistry of the gas-phase reactions between CHF₂CF₂OCH₂CF₃ and OH radical using a new hybrid density functional M06-2X/6-31+G(d,p) and G2(MP2)//M06-2X/6-31+G(d,p) methods. The most stable conformer of CHF₂CF₂OCH₂CF₃ is considered in our study and the possible H-abstraction reaction channels are identified. Each reaction channel shows an indirect H-abstraction reaction mechanism via the formation of pre-reactive complex. The rate coefficients are determined for the first time over a wide range of temperature 250–1000 K. At 298 K, the calculated total rate coefficient of k_OH = 1.01×10^?14 cm³ molecule^?1 s^?1 is in good agreement with the experimental results. The heats of formation for CHF₂CF₂OCH₂CF₃ and CF₂CF₂OCH₂CF₃ and CHF₂CF₂OCHCF₃ radicals are estimated to be -1739.25, -1512.93 and -1523.94 kJ mol^?1, respectively. The bond dissociation energies of the two C-H bonds are C(-H)F₂CF₂OCH₂CF₃: 423.34 kJ mol^?1 and CHF₂CF₂OC(-H)HCF₃: 411.87 kJ mol^?1. The atmospheric lifetime of CHF₂CF₂OCH₂CF₃ is estimated to be around 4.5 years and the 100-year time horizon global warming potentials of CHF₂CF₂OCH₂CF₃ relative to CO₂ is estimated to be 601.     

Di-urethanesil hybrid electrolytes doped with Mg(CF3SO3)2

Two siloxane-based di-urethanesil frameworks incorporating poly(oxyethylene) (POE) chains have been synthesized by the sol–gel process and doped with magnesium triflate (Mg(CF₃SO₃)₂) with the goal of developing electrolytes for the fabrication of solid-state rechargeable magnesium batteries. In these matrices, short POE chains are covalently bonded to the siloxane network via urethane linkages. The xerogels have been represented by the notation d-Ut(Y) _n Mg(CF₃SO₃)₂, where Y?=?300 and 600 represents the average molecular weight of the POE chains and n stands for salt composition (molar ratio of OCH₂CH₂ units per Mg²⁺). Xerogels with compositions ranging from 2?≤?n?<?∞ were prepared. A crystalline POE/Mg(CF₃SO₃)₂ complex of unknown stoichiometry is formed in the d-Ut(300) _n Mg(CF₃SO₃)₂ materials with n?≤?6 and in the d-Ut(600) _n Mg(CF₃SO₃)₂ materials with n?≤?5. The organically modified silicate electrolytes with the highest conductivity of the d-Ut(300) _n Mg(CF₃SO₃)₂ and d-Ut(600) _n Mg(CF₃SO₃)₂ series are the samples with n?=?6 (3.9?×?10^?8 S cm^?1 at 26 °C and 8.7?×?10^?5 S cm^?1 at 97 °C) and n?=?100 (2.63?×?10^?7 S cm^?1 at 20 °C and 1.4?×?10^?5 S cm^?1 at 85 °C), respectively. Since the electrolytes for Mg batteries that have been proposed up to now have many intrinsic problems and although the room temperature conductivity values exhibited by the systems developed in the present study are still low in view of practical application, this work opens new directions for the development of solid-state Mg ion electrolytes.     

Manifestation of resonance dipole-dipole interaction in spectra of low-temperature molecular mixtures of C2F6 in CF4 and CF4 in C2F6

We have measured IR absorption spectra of solutions C₂F₆ in CF₄ (T = 178 K) and CF₄ in C₂F₆ (T = 173 K) in the overtone range of the spectrum. We have studied how the resonance dipole-dipole interaction affects the formation of contours of bands that correspond to transitions to states involving the vibrations ν₁₀(C₂F₆) and ν₃(CF₄), which are strong in the dipole absorption. For the system C₂F₆ in liquid CF₄, the state ν₂ + ν₁₀(C₂F₆) resonantly interacts with the state ν₂(C₂F₆) + ν₃(CF₄), and, for the system CF₄ in liquid C₂F₆, the state ν₁ + ν₃(CF₄) resonantly interacts with the state ν₁(CF₄) + ν₁₀(C₂F₆). The contours of the bands ν₂ + ν₁₀ (C₂F₆) in the spectrum of the mixture with CF₄ and of the bands ν₁ + ν₃(CF₄) in the spectrum of the mixture with C₂F₆ have been calculated.     

Computational study on the kinetics of OH initiated oxidation of methyl difluoroacetate (CF2HCOOCH3)

The kinetics of hydrogen atom abstraction reactions of methyl difluoroacetate (CF₂HCOOCH₃) by OH radical has been studied by quantum mechanical method. The geometry optimisation and frequency calculation of the titled compound was performed with density functional theory using hybrid meta density functional MPWB1K with 6-31+G(d,p) basis set. Transition states have been determined and intrinsic reaction coordinate (IRC) calculation has been performed to ascertain that the transition from reactants to products was smooth through the corresponding transition state. Energy values are refined by making single point energy calculation at G3B3 level of theory and an energy level diagram is constructed. The standard enthalpies of formation of reactants and other species formed during the reaction were calculated using isodesmic method. The rate constants are calculated using canonical transition state theory and the overall rate constant is determined to be 1.35×10^?13 cm³ molecule^?1 s^?1 at 298 K and 1 atmospheric pressure. Tunnelling has been taken into account in the determination of the rate constant because it plays a critical role at low temperature especially when transfer of hydrogen takes place. The calculated value is found to be in good agreement with the experimentally determined value of 1.48×10^?13 cm³ molecule^?1 s^?1.     

Fire suppression using trifluoroiodomethane (CF3I)-carbon dioxide (CO2) mixtures

With the regulatory prohibition for using Halon 1301 (CF₃Br) in fire suppression systems onboard newly certified aircraft, significant research efforts have been undertaken to develop suitable halon replacements with comparable suppression performance that are also eco-friendly with low Ozone Depletion Potential (ODP) and Global Warming Potential (GWP). This paper determined the fire suppression effectiveness for mixtures of trifluoroiodomethane (CF₃I) with carbon dioxide (CO₂) under development as a drop-in halon replacement for onboard aircraft fire suppression systems. Through both experimental measurements and flame simulations using detailed chemical kinetics, we demonstrated that the extinguishment performance of CF₃I-CO₂ blends can be superior to that of the individual components alone. The extinction concentrations were determined for different CF₃I-to-CO₂ ratios introduced into ambient air using a heptane cup burner. The extinction concentrations for pure CF₃I in air (3.36 ± 0.13% vol.) and CO₂ in air (20.74 ± 0.64% vol.) are in close agreement with previously reported values, and first-time extinction concentration data for CF₃I-CO₂ blends are reported. To elucidate important reaction pathways, detailed chemical mechanisms have been compiled for modeling methane-, propane- and heptane-air flame inhibition at ambient conditions. These mechanisms were constructed from published sub-mechanisms for C₇ and C₁-C₃ hydrocarbons and hydrofluorocarbons with additional oxidation chemistry developed for trifluoroiodomethane. The latter sub-mechanism contains 14 species and 91 reactions. Using the CANTERA software package, critical concentration values of CF₃I-CO₂ mixtures in air for extinguishing methane, propane, and n-heptane counterflow flames were determined and compared against experimental non-premixed flame extinction data.     

Reactions induced in (CF3I) n clusters by femtosecond UV laser pulses

The excitation and ionization of CF₃I molecules and their clusters by femtosecond UV laser pulses is studied. It is concluded that the types of excitation of free CF₃I molecules and their clusters by femtosecond UV laser pulses are different. The composition and kinetic energy of ion products observed upon the ionization of (CF₃I) _n clusters by femtosecond pulses are found to differ considerably from those obtained upon ionization by nanosecond pulses. It is shown that the molecular I ₂ ⁺ ion is produced in reactions induced in (CF₃I) _n clusters by UV radiation. Using the pump-probe method, we found the two channels of producing I ₂ ⁺ ions with characteristic times ??₁ ?? 1 ps and ??₂ ?? 7 ps. A model of the reactions under study proposed in the paper is consistent with our experimental results.     

Exploring the reaction channels between arsine and the hydroxyl radical

The aim of this study was to present the reaction mechanism channels between arsine (AsH₃) and hydroxyl (OH) which was evaluated at CCSD(T)/CBS//CCSD/cc-pVTZ level. One potential channel is the hydrogen abstraction pathway (R1), leading to AsH₂ and H₂O products, which occurs due to the formation of an entrance complex (AsH₃OH) followed by a 1,2-hydrogen shift pathway (involving the proton transfer from the arsine group to hydroxyls, with one leading to the products). Additional channels are accessed via H-elimination pathways of the entrance complexes, forming arsinous acid (AsH₂OH; R2) and arsine oxide (AsH₃O; R3). In this respect, R2 is the only exoergic route of the three exit channels, representing the major branching ratio at 200–1000 K and, after 2000 K, R1 increases gradually becoming the major route of this reaction. In contrast, even at 4000 K, R3 is a highly unfeasible pathway. Therefore, the information predicted here provides new insights into the neutral–neutral chemical reaction dynamics regarding the Group V hydrides. On the other side, the R2 pathway may have some potential to solve the arsine oxidation puzzle as a possible primary pathway to the arsenic-oxygen species formation.     

DFT study of self-coupling reaction of CF2(ads) coadsorbed on Cu(111) surface for forming CF2=CF2(g)

Total energy calculations based on the density functional theory (DFT) with ultrasoft pseudopotential, generalized gradient spin-polarized approximation and the partial structural constraint path minimization (PSCPM) method were carried out to establish the energetically more favorable reaction pathways for the self-coupling reaction of coadsorbed CF_2(ads) leading to the formation of CF₂=CF_2(ads) on the Cu(111) surface. In addition, the calculated electronic properties, namely partial density of states (PDOS), suggest that the initial breaking of the Cu(111)–CF_2(ads) bond associating with the electron delocalization on the Cu(111) surface and the electron transfer from Cu(111) to both units of CF_2(ads) are factors controlling the energy barrier for self-coupling reaction. Finally, the calculated energy barrier (0.310 eV) for the self-coupling reaction of CF_2(ads) coadsorbed on the Cu(111) surface in comparison with that (0.204 eV) for the single α-fluoride elimination of adsorbed CF_3(ads) on the Cu(111) surface qualitatively manifests that the formation of CF₂ = CF_2(g) at 250 K is limited by the self-coupling reaction of coadsorbed CF_2(ads) instead of the single α-fluoride elimination of adsorbed CF_3(ads).     

Theoretical studies on atmospheric chemistry of HFE‐347mcc3: reactions with OH radicals and Cl atoms

Detailed theoretical investigation has been performed on the mechanism, kinetics and thermochemistry of the gas phase reactions of CF₃CF₂CF₂OCH₃ (HFE‐347mcc3) with OH radicals and Cl atoms using M06‐2X/6‐31 + G(d,p) level of theory. Reaction profiles are modeled including the formation of pre‐reactive and post‐reactive complexes at entrance and exit channels, respectively. Using group‐balanced isodesmic reactions, the standard enthalpies of formation for species are also reported. The calculated bond dissociation energy for C―H bond is in good agreement with previous data. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–1000 K. At 298 K, the calculated rate coefficients are in good agreement with the experimental results. The atmospheric life time of HFE‐347mcc3 is estimated to be 4.4 years. Copyright © 2014 John Wiley & Sons, Ltd.     

A density functional theory study of CF3CH2I adsorption and reaction on Ag(111)

The adsorption and reaction behaviors of CF₃CH₂I on Ag(111) were systematically studied by density functional theory (DFT) calculations. Physical adsorption of CF₃CH₂I on Ag(111) occurs due to the weak interactions between surface Ag atoms and iodine atom of CF₃CH₂I; while strong chemisorption occurs for CF₃CH₂ fragment on Ag(111). Electronic analysis indicates that the singly occupied molecular orbital (SOMO) of CF₃CH₂ strongly interacts with the surface Ag atoms. It is very interesting to find that the most stable structures of CF₃CH₂ on Ag(111) locate at the top site, instead of the hollow sites. This might be attributed to the facts that CF₃CH₂ adsorbed at the top site will maximize the sp³-type hybridization, and the possible weak interaction between the fluorine lone pair electrons of p orbitals for CF₃CH₂ and surface Ag(111) occurs, which is supported by the charge density difference (CDD) analysis with a low isosurface value. We propose that the charge density difference (CDD) analysis with a high or low isosurface value can be widely applied to analyze the strong or weak electronic interactions upon adsorption. Transition state calculations suggested that the energy barrier of CF bond rupture for CF₃CH₂I on Ag(111) (1.44 eV) is much higher than that of CI bond breakage for CF₃CH₂I (0.43 eV); and the activation energy of the CF bond dissociation for CF₃CH₂(a) is 0.67 eV.     

Reactions of excited I*(2P1/2) and unexcited I(2P3/2) iodine atoms in perfluoroalkyl radicals

A method of investigating reactions of excited and unexcited atoms is discussed. It is based on pulsed photolysis of molecules with simultaneous passage of laser radiation through the working medium. The method proposed is used to investigate the reactions that accompany the photolysis of the molecules RI(CF₃I, n-C₃F₇I, i-C₃F₇I). The rate constants of the recombination of iodine atoms into I₂ in the presence of RI molecules are calculated for the atoms I(²P_3/2) and I*(²P_1/2), as are the recombination constants of the radicals R into R₂ and with the atoms I*(²P_1/2) and I(²P_3/2) into the RI molecule. It is shown that the I(²P_3/2) atoms are much more active in the recombination into Ia and RI than the I*(²P_1/2) atoms. The role of the investigated reactions in the kinetics of a photodissociation iodine laser (PDIL) is discussed. The results are compared with the published data.     

MJ and collision energy dependent attenuation of Rg (3P2) by CF3Br

The total attenuation cross-section of Rg (³P₂) (Rg = Ar, Kr) by the collision with CF₃Br is measured as a function of the magnetic sub level M_J of Rg (³P₂) and the collision energy. For Ar (³P₂), the attenuation process indicates a M_J dependence, in particular, the cross-section of the M_J = 0 state is lower compared with that for other states. On the other hand, Kr (³P₂) shows no M_J dependent attenuation.     

Cup-burner flame structure and extinguishment by CF3Br and C2HF5 in microgravity

The effects of fire-extinguishing agents CF₃Br and C₂HF₅ on the structure and extinguishing processes of microgravity cup-burner flames have been studied numerically. Propane and a propane–ethanol–water fuel mixture, prescribed for a Federal Aviation Administration (FAA) aerosol can explosion simulator test, were used as the fuel. The time-dependent, two-dimensional numerical code, which includes a detailed kinetic model (177 species and 2986 reactions), diffusive transport, and a gray-gas radiation model, revealed unique flame structure and predicted the minimum extinguishing concentration of agent when added to the air stream. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilized a trailing flame. The calculated flame temperature along the trailing flame decreased downstream due to radiative cooling, causing local extinction at <1250 K and flame tip opening. As the mole fraction of agent in the coflow (X_a) was increased gradually: (1) the premixed-like reaction kernel weakened (i.e., lower heat release rate) (but nonetheless formed at higher temperature); (2) the flame base stabilized increasingly higher above the burner rim, parallel to the axis, until finally blowoff-type extinguishment occurred; (3) the calculated maximum flame temperature remained at nearly constant (≈1700 K) or mildly increased; and (4) the total heat release of the entire flame decreased (inhibited) for CF₃Br but increased (enhanced) for C₂HF₅. In the lifted flame base with added C₂HF₅, H₂O (formed from hydrocarbon-O₂ combustion) was converted further to HF and CF₂O through exothermic reactions, thus enhancing the heat-release rate peak. In the trailing flame, “two-zone” flame structure developed: CO₂ and CF₂O were formed primarily in the inner and outer zones, respectively, while HF was formed in both zones. As a result, the unusual (non-chain branching) reactions and the combustion enhancement (increased total heat release) due to the C₂HF₅ addition occurred primarily in the trailing diffusion flame.     

Extended X‐ray absorption fine structure and multiple‐scattering simulation of nickel dithiolene complexes Ni[S2C2(CF3)2]2n (n = −2, −1, 0) and an olefin adduct Ni[S2C2(CF3)2]2(1‐hexene)

A series of Ni dithiolene complexes Ni[S₂C₂(CF₃)]₂ⁿ (n = ?2, ?1, 0) ( 1 , 2 , 3 ) and a 1‐hexene adduct Ni[S₂C₂(CF₃)₂]₂(C₆H₁₂) ( 4 ) have been examined by Ni K‐edge X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine‐structure (EXAFS) spectroscopies. Ni XANES for 1 – 3 reveals clear pre‐edge features and approximately +0.7 eV shift in the Ni K‐edge position for `one‐electron' oxidation. EXAFS simulation shows that the Ni—S bond distances for 1 , 2 and 3 (2.11–2.16 Å) are within the typical values for square planar complexes and decrease by ～0.022 Å for each `one‐electron' oxidation. The changes in Ni K‐edge energy positions and Ni—S distances are consistent with the `non‐innocent' character of the dithiolene ligand. The Ni—C interactions at ～3.0 Å are analyzed and the multiple‐scattering parameters are also determined, leading to a better simulation for the overall EXAFS spectra. The 1‐hexene adduct 4 presents no pre‐edge feature, and its Ni K‐edge position shifts by ?0.8 eV in comparison with its starting dithiolene complex 3 . Consistently, EXAFS also showed that the Ni—S distances in 4 elongate by ～0.046 Å in comparison with 3 . The evidence confirms that the neutral complex is `reduced' upon addition of olefin, presumably by olefin donating the π‐electron density to the LUMO of 3 as suggested by UV/visible spectroscopy in the literature.     

Absorption spectrum of the (CF4) dimer in liquid argon solution

The concentration dependence of the shape of absorption bands in the spectrum of CF₄ in liquid argon is studied in the concentration range (0.01–17)×10^?3 molar fractions at 93 K. In all spectral regions related to ν₃, the shape of the spectral function is determined, along with the Fermi resonance 〈ν_i,ν₃+1,ν₄|≈〈νi,ν₃,ν ₄+2|, by the resonance dipole-dipole interaction. In the spectral region of the Fermi doublet ν ₁+ν₃≈ ν₁+2ν₄, the spectrum of the contact (CF₄)₂ dimer is identified. Agreement between this spectrum and the calculated spectrum is achieved by simultaneously taking intramolecular and intermolecular resonances into account. The distance R _C-C in the dimer is 4.85(15) Å. The calculations of the spectra of (¹²CF₄)₂ and (¹³CF₄?¹²CF₄) dimers with this value of R _C-C in the region ν ₃≈2ν₄ agree with the experiment.     

Double photoionisation spectra of HI,CH3I and CF3I from TOF-PEPECO measurements

Double photoionisation spectra of HI, CH₃I and CF₃I have been measured by the TOF-PEPECO technique, providing complete information on electron energy distributions. The lowest energy states of HI²⁺ and CH₃I²⁺ are identified and their vibrations are resolved. Possible reasons for the markedly different CF₃I spectrum are discussed. There is evidence for atomic autoionisation of iodine as a pathway contributing to the double photoionisation.     

Dussertite BaFe3+3(AsO4)2(OH)5—a Raman spectroscopic study of a hydroxy‐arsenate mineral

The mineral dussertite, a hydroxy‐arsenate mineral with formula BaFe³⁺₃(AsO₄)₂(OH)₅, has been studied by Raman spectroscopy complemented with infrared spectroscopy. The spectra of three minerals from different origins were investigated and proved to be quite similar, although some minor differences were observed. In the Raman spectra of the Czech dussertite, four bands are observed in the 800–950 cm⁻¹ region. The bands are assigned as follows: the band at 902 cm⁻¹ is assigned to the (AsO₄)³⁻ν₃ antisymmetric stretching mode, the one at 870 cm⁻¹ to the (AsO₄)³⁻ν₁ symmetric stretching mode, and those at 859 and 825 cm⁻¹ to the As‐OM^{2 + /3+} stretching modes and/or hydroxyl bending modes. Raman bands at 372 and 409 cm⁻¹ are attributed to the ν₂ (AsO₄)³⁻ bending mode and the two bands at 429 and 474 cm⁻¹ are assigned to the ν₄ (AsO₄)³⁻ bending mode. An intense band at 3446 cm⁻¹ in the infrared spectrum and a complex set of bands centred upon 3453 cm⁻¹ in the Raman spectrum are attributed to the stretching vibrations of the hydrogen‐bonded (OH)⁻ units and/or water units in the mineral structure. The broad infrared band at 3223 cm⁻¹ is assigned to the vibrations of hydrogen‐bonded water molecules. Raman spectroscopy identified Raman bands attributable to (AsO₄)³⁻ and (AsO₃OH)²⁻ units. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical study on the mechanism and kinetics of atmospheric reactions NH2OH + OOH and NH2CH3 + OOH

Mechanism and kinetics of NH₂OH + OOH and NH₂CH₃ + OOH reactions were studied at the B3LYP and M062X levels of theory using the 6-311++G(3df, 3pd) basis set. The NH₂OH + OOH and NH₂CH₃ + OOH reactions proceed through different paths which lead to different products. Transition state structure and activation energy of each path were calculated. The calculated activation energies of hydrogen abstraction reactions were smaller than 25 kcal/mol and of substitution reactions are in the range of 50–70 kcal/mol. The rate constants were calculated using transition state theory (TST) modified for tunneling effect at 273–2000 K.