COF2 Research Articles

Pyrolysis mechanism of 1,1,1,2-tetrafluoroethane and 1,1,1,2-tetrafluoroethane/carbon dioxide as working fluids for transcritical power cycles: Insights from reactive force field molecular dynamics and density functional theory studies

Carbon dioxide-based mixtures in transcritical power cycle systems can enhance thermodynamic performance but may pose risks of thermal decomposition, potentially compromising system performance and safety. This study investigates the pyrolysis mechanism of 1,1,1,2-tetrafluoroethane (R134a)/carbon dioxide (CO₂), a typical CO₂-based mixture, using reactive force field molecular dynamics (ReaxFF-MD) simulations and density functional theory (DFT). ReaxFF-MD simulations are conducted at pressures ranging from 4 to 12 MPa and temperatures between 1800 K and 3200 K for various fluid compositions, including pure R134a and R134a/CO₂ mixtures at mole ratios of 0.7/0.3, 0.5/0.5, and 0.3/0.7. The effects of temperature, pressure, and composition on the thermal decomposition of both pure R134a and R134a/CO₂ mixtures are examined, with particular focus on behavior at 8 MPa. In the thermal decomposition of R134a/CO₂ mixtures, CO₂ inhibits the formation of F radicals and reduces their concentration through chemical reactions, thereby suppressing R134a decomposition. Pure R134a decomposes into primary products such as hydrogen fluoride (HF), fluorine (F), tetrafluoroethylene (C2HF4), trifluoromethyl radicals (CF3), and diatomic carbon (C2). The addition of CO2 results in the formation of additional products, including carbonyl fluoride (COF), oxygen (O), hydroxyl (HO), and formyl radicals (CHO). The decomposition pathways involve two reaction types: self-decomposition reactions dominate initially, while extraction reactions become more prominent later. Using the DFT approach, reaction energy barriers are analyzed to corroborate the ReaxFF-MD simulation findings. Moreover, the apparent activation energies for these reactions are quantified using first-order kinetics based on the Arrhenius equation, indicating that the thermal decomposition of R134a/CO2 mixtures is more challenging than that of pure R134a.

DFT study of adsorption and potential detection of carbonyl fluoride on B-doped aluminum nitride nanosheets

Carbonyl fluoride (COF2) is a decomposition product that can be used to find failures in gas-insulated switchgear equipment. In this study, we applied Density Functional Theory (DFT) calculations to examine the suitability of pristine and boron-doped aluminum nitride nanosheets (AlNNS) for COF2 adsorption and sensing applications. Our investigation suggested a dissociative COF2 adsorption on pristine AlNNS, resulting in important adsorption energy (–2.19 eV), the releasing of a fluorine atom from the molecule and formation of new C–N, O–Al and F–Al bonds. Two preferential chemisorption geometries were achieved on the B-doped N-vacancy monolayer (B-vN-AlNNS), with adsorption energies of –1.04 and –3.44 eV. In the first geometry, only an O–B bond was formed, whereas in the another one similar interactions as in COF2/AlNNS took place. Furthermore, we analyzed the evolution of electronic properties in order to evaluate the performance of these nanosheets for COF2 detection purposes. Our results showed significant modifications in both energy gap and work function only after COF2 adsorption on B-vN-AlNNS. Finally, charge transfer analysis revealed electron exchange from the studied surfaces to the gas molecule. These findings suggest that B-doped AlNNS exhibits good performance for COF2 detection, and could encourage further experimental research to develop efficient sensing materials.

Adsorption behavior of HFCO and COF2 gasses on pristine, Al-doped, and N-doped (8, 0) single-wall carbon nanotubes and pristine aluminum nitride nanotube: A first-principles study

The detection of organic pollutants in the environment is crucial due to their significant impact on human health. Formyl fluoride (HFCO) and carbonyl fluoride (COF2) are toxic gasses that contribute to stratospheric ozone depletion. To explore a potential sensor material for these compounds, the adsorption properties of HFCO and COF2 on pristine (8, 0) single-walled carbon nanotubes (SWCNTs), aluminum-doped SWCNTs (Al-SWCNTs), nitrogen-doped SWCNTs (N-SWCNTs), and aluminum nitride nanotube (AlNNTs) were investigated using density functional theory (DFT) calculations. Obtained structural and electronic results reveal no significant after HFCO and COF2 adsorption on pristine SWCNT. However, the conductivity and polarizability of Al- SWCNT increases throw HFCO and COF2 adsorption. It was shown that this adsorption strongly depends on molecular orientation toward SWCNT. Structural and electronic findings show that studied molecules undergoes a physical adsorption to N- SWCNT. However, AlNNT was also found to show significant changes in structural and electronic properties after HFCO and COF2 adsorption. This adsorption leads to a significant (nearly 45%) reduction in the HOMO-LUMO gap of AlNNTs. Therefore, it is proposed from this study that Al-SWCNTs and AlNNTs are promising candidates for HFCO and COF2 gas sensors. Moreover, AlNNTs exhibit intrinsic detection capabilities without structural manipulation via doping which makes AlNNTs particularly attractive for sensor applications. Moreover, the capability of AlNNT without manipulating makes this nanotube a good and easy made candidate for these compounds adsorption.

Exploring the sensing potential of Fe-decorated h-BN toward harmful gases: a DFT study.

Gas sensing technology has a broad impact on society, ranging from environmental and industrial safety to healthcare and everyday applications, contributing to a safer, healthier, and more sustainable world. We studied pure and Fe-decorated hexagonal boron nitride (h-BN) gas sensor for monitoring of carbon-based gases using density functional theory (DFT). The calculations utilized the Generalized Gradient Approximation with the Perdew-Burke-Ernzerhof (GGA-PBE) exchange-correlation functional. The novelty of our study lies in the investigation of the adsorption of harmful gases such as carbonyl sulfide, carbinol, carbimide, and carbonyl fluoride on both pure and Fe-decorated h-BN. The deviation in structural, electronic, and adsorption properties of h-BN due to Fe decoration has been studied along with the sensing ability to design said material towards carbon monoxide (CO), carbon dioxide (CO2), carbonyl sulfide (COS), carbinol, (CH4O), carbimide (CH2N2), and carbonyl fluoride (CF2O) gases. Gases such as CO, COS, CH2N2, and CF2O exhibited chemisorption, while CO2, and CH4O exhibited physisorption behavior. The introduction of Fe altered the semiconductor properties of h-BN and rendered it metallic. Enhanced electronic properties were observed due to a robust hybridization occurring between the d-orbitals of Fe-decorated BN and the gas molecules. The extended recovery periods observed for gases, aside from CO2, indicate their adhesive interactions with Fe-decorated h-BN. The reduction in desorption duration as temperature rises allows Fe-decorated h-BN to function as a reversible gas sensor. This research opens up a novel pathway for the synthesis and advancement of cost-effective, environmentally friendly double-atom catalysts with high sensitivity for capturing and detecting molecules such as CO, COS, CH2N2, CO2, CH4O, and CF2O.

Symmetry-based method for the derivation of the vibration–rotation kinetic energy operator and energy levels calculation of carbonyl fluoride from a new ab initio potential energy surface

A simple and intuitive symmetry-based method for deriving the vibration–rotation kinetic energy operator (in polyspherical coordinates) for a general polyatomic molecule using the kinetic energy of a triatomic molecule was considered. Two vectors define the molecule-fixed coordinate system. For example, those vectors can determine positions of two atoms with respect to the third atom. By rotating the coordinate system, it is possible to obtain expressions that relate coefficients determining the kinetic energy in two coordinate systems. Those expressions let us obtain formulas for kinetic energy of general polyatomic molecules from kinetic energy of the triatomic molecules. Vibrational Energy levels of COF2 molecules were calculated from new ab initio potential energy surface. The comparison of the calculated and experimental vibrational energy levels is also reported.

Visible-Light-Induced DDQ-Catalyzed Fluorocarbamoylation Using CF3SO2Na and Oxygen.

The synthesis of carbamoyl fluorides via visible-light induced DDQ catalysis of secondary amines is described. This protocol employs sodium trifluorosulfinate and molecular oxygen for the in situ generation of carbonyl difluoride, which is reacted with amines to afford the corresponding carbamoyl fluorides efficiently. Moreover, carbamoyl fluorides are easily transformed to synthetically useful carbonyl compounds under mild reaction conditions.

Gas-phase epoxidation of Hexafluoropropene using molecular oxygen and alkali doped CuO catalyst: Mechanism and kinetics

The study investigated the partial oxidation of hexafluoropropene over CuO catalyst with molecular oxygen in a continuous flow fixed bed reactor. The catalysts were characterized using various techniques, and the results confirmed catalyst's structure-reactivity correlation. The major products were hexafluoropropene oxide (HFPO) and carbonyl fluoride, with minor trifluoroacetyl fluoride produced when the catalyst had significantly declined in primary activity. The maximum selectivity of 52.5% HFPO was obtained at 13.4% hexafluoropropene conversion at 4.5 bar and 453 K. The proposed redox mechanism kinetic model was in adequate agreement with the experimental data (R2 = 0.97 for COF2 and 0.67 for HFPO).

Atmospheric oxidation of unsaturated hydrofluoroethers initiated by OH radicals

Hydrofluoroethers (HFEs) are perfluorinated chemicals that were developed as alternative for chlorofluorocarbons (CFCs) in various applications. Among notable unsaturated HFEs are perfluoro methyl vinyl ether (PMVE, CF3OCFCF2) and perfluoro ethyl vinyl ether (PEVE, C2F5OCF = CF2). During the implementation of PMVE and PEVE, they spill and release to the atmosphere. Due to the tendency of perfluorinated compounds to have strong infrared absorption features and long atmospheric lifetimes, they are among the most potent greenhouse gases. Thus, it is important to accurately assess their atmospheric sink routes in order to assess their impact on climate change. Herein, we illustrated detailed mechanistic pathways and developed kinetic models with the underlying aim to comprehend the atmospheric fate of the title HFEs and the likely products of decomposition. It was found that the production of main products to stem from the addition of OH radical to the inner carbon-carbon double bond atoms. Atmospheric lifetimes of PMVE and PEVE were calculated to be ∼23 and ∼56 h; respectively. Time-dependent molar yields are acquired for the experimentally major products; namely carbonyl fluoride (CF2O), perfluorinated glyoxal (CFOCFO), perfluorinated methylformates (CF3OCFO and CF3CF2OCFO). Photochemical Ozone Creation Potentials (POCPs) of PMVE and PEVE were calculated to be 1.78 and 1.18, respectively. Obtained results tap into efforts that aim to understand the atmospheric chemistry cycles of perfluorinated chemicals in general.

Chemisorption and physisorption studies of carbonyl fluoride and carbon disulfide on C19 X (X = Zn, Co and Sc) nanocage by DFT-based calculation

In this study, we used the DFT calculations and the B3LYP functional to examine the adsorption of the CS2 and COF2 molecules on the surface of the clusters C20 and C19X (X = Zn, Co, Sc). The results have been investigated by the net charge transfer, frontier orbitals, the binding energy, electrical and thermodynamic properties. Although CS2 and COF2 complexes on free C20 nanocages showed slightly binding energies (−0.163 eV), doping them with (Zn, Co and Sc) transition metal atoms improved the binding energy because the substitution of carbon atoms with metal atoms (Zn, Co, Sc), C19X (X = Zn, Co, Sc) nanocages were found to be more stable. Adsorption of COF2 on C19Sc produced the best binding energy (−2.667 eV). Also, natural bond orbital (NBO) analysis showed that the best charge transfer was (−0.602e) which was related to the formation of COF2−C19Sc complex. Furthermore, the least HOMO, LUMO energy gap between free nanocages (C20, C19Zn, C19Co, C19Sc) is 5.36 eV (C19Co and C19Sc). The thermodynamic analyses indicated that all of the adsorption processes examined were exothermic because of the negative enthalpy.

Understanding the kinetics and atmospheric degradation mechanism of chlorotrifluoroethylene (CF2CFCl) initiated by OH radicals.

The atmospheric degradation of chlorotrifluoroethylene (CTFE) by OH˙ was investigated using density functional theory (DFT). The potential energy surfaces were also defined in terms of single-point energies derived from the linked cluster CCSD(T) theory. With an energy barrier of -2.62 to -0.99 kcal mol-1 using the M06-2x method, the negative temperature dependence was determined. The OH˙ attack on Cα and Cβ atoms (labeled pathways R1 and R2, respectively) shows that reaction R2 is 4.22 and 4.42 kcal mol-1, respectively, more exothermic and exergonic than reaction R1. The main pathway should be the addition of OH˙ to the β-carbon, resulting in ˙CClF-CF2OH species. At 298 K, the calculated rate constant was 9.87 × 10-13 cm3 molecule-1 s-1. The TST and RRKM calculations of rate constants and branching ratios were performed at P = 1 bar and in the fall-off pressure regime over the temperature range of 250-400 K. The formation of HF and ˙CClF-CFO species via the 1,2-HF loss process is the most predominant pathway both kinetically and thermodynamically. With increasing temperature and decreasing pressure, the regioselectivity of unimolecular processes of energized adducts [CTFE-OH]˙ gradually decreases. Pressures greater than 10-4 bar are often adequate for assuring saturation of the estimated unimolecular rates when compared to the RRKM rates (in high-pressure limit). Subsequent reactions involve the addition of O2 to the [CTFE-OH]˙ adducts at the α-position of the OH group. The [CTFE-OH-O2]˙ peroxy radical primarily reacts with NO and then directly decomposes into NO2 and oxy radicals. "Carbonic chloride fluoride", "carbonyl fluoride", and "2,2-difluoro-2-hydroxyacetyl fluoride" are predicted to be stable products in an oxidative atmosphere.

Reactions of oxygen atoms with fluoroform and its radiolysis products: matrix isolation and ab initio study.

The investigation of the reactions of oxygen atoms with fluoroform (CHF3) molecules and products of their degradation present significant interest for better understanding of the impact of chemically inert fluorinated compounds on atmospheric chemistry and may provide a deeper insight into mechanisms of chemical processes occurring under the action of hard UV and ionizing radiation. In the present study we applied a matrix isolation technique with FTIR spectroscopic detection combined with ab initio calculations to address this issue. It was found that the reactions of "hot" (translationally excited) O(1D) atoms produced by X-ray or UV radiation from appropriate precursors (N2O or H2O) resulted in the formation of carbonyl fluoride (COF2) and its complex with HF. The complex was detected and characterized for the first time. Singlet oxygen atoms also probably react with the products of radiation-induced degradation of fluoroform (CF3 and CF2). Additionally, the reaction of "hot" O(3P) atoms with fluoroform may occur to a certain extent yielding the CF3 radical. No evidence for the reactions of thermal O(3P) atoms with CHF3 or products of its degradation was found under the experimental conditions used. The implications of the results of this model study for understanding the evolution of fluoroform in the upper layers of the stratosphere and ionosphere are discussed.

Reaction of Cl Atom with c-C5F8 and c-C5HF7: Relative and Absolute Measurements of Rate Coefficients and Identification of Degradation Products.

Partially and fully fluorinated olefins are a class of compounds with relatively short atmospheric lifetimes and low 100-year global warming potentials, compared to their saturated predecessors, which are used or considered as refrigerants, propellants, solvents, and other end-uses. The cyclic unsaturated compounds c-C5F8 and c-C5HF7 are currently under consideration as etching agents for the semiconductor industry. In this study, we expand on our previous work on the reaction of the OH radical with c-C5F8 and c-C5HF7 and report the rate coefficients, k, for the gas-phase reaction of the Cl atom with c-C5F8 and c-C5HF7 over a range of temperature (245-367 K) and pressure (100-200 Torr of He or N2 and 0 to 4.8 Torr O2) using a pulsed laser photolysis-resonance fluorescence (PLP-RF) technique. In addition, a relative rate (RR) technique, employing multiple reference compounds, was used to study the Cl atom reactions at 296 K, 100 and 630 Torr (N2 or air) total pressure. Reaction rate coefficients, k1, of the Cl atom reaction with c-C5F8 were found to be independent of pressure, over the pressure range used in this work, with k1(296 K), derived as an average of results from the PLP-RF and RR techniques being (1.07 ± 0.02) × 10-12 cm3 molecule-1 s-1 and k1(T) = (7.76 ± 0.73) × 10-13 × (exp[(98 ± 26)/T]) cm3 molecule-1 s-1, where the quoted error limits represent the 2σ data precision. Rate coefficients, k2, for the Cl atom + c-C5HF7 reaction were measured to be k2(296 K) = (4.61 ± 0.10) × 10-12 cm3 molecule-1 s-1 and k2(T) = (7.42 ± 0.89) × 10-13 × (exp[(540 ± 32)/T]) cm3 molecule-1 s-1. The Cl atom temporal profiles, observed with the PLP-RF technique, indicate that the Cl atom with c-C5F8 and c-C5HF7 reactions lead to adduct formation. The equilibrium constants for adduct formation were derived in this work, and a second-law analysis was used to obtain ΔH and ΔS values of -18.5 ± 0.4 kcal mol-1, -30.9 ± 1.2 cal K-1 mol-1, and -13.9 ± 0.5 kcal mol-1, -27.6 ± 1.1 cal K-1 mol-1 for the c-C5F8 and c-C5HF7 reactions, respectively. The Cl-initiated degradation of c-C5F8 and c-C5HF7 in the presence of O2 was studied and stable products were identified via infrared spectroscopy using experimental or theoretically derived spectra from our previous OH reaction work. For c-C5F8, FC(O)CF2CF2CF2C(O)F and FC(O)C(O)F were observed with molar yields of 0.80 and 0.10, respectively. For c-C5HF7, we observed the formation of HC(O)CF2CF2CF2C(O)F and HC(O)C(O)F with a combined molar yield of 0.72. Carbonyl difluoride, F2CO, was also a major product in the decomposition of c-C5F8 and c-C5HF7. The oxidation mechanism of the Cl-initiated degradation of c-C5F8 and c-C5HF7 is discussed. Based on the combined findings from this and our previous work, the atmospheric implications from the use of c-C5F8 and c-C5HF7 are presented.

The potential of thermal desorption-GC/MS-based analytical methods for the unambiguous identification and quantification of perfluoroisobutene and carbonyl fluoride in air samples.

The reactive gases perfluoroisobutene and carbonyl fluoride are highly toxic and difficult to analyze in air. For this paper, the available sampling and analysis methods involving gas chromatography/mass spectrometry were investigated for their potential to give unambiguous identification and quantification of perfluoroisobutene and carbonyl fluoride, for which no such methods exist. Although high concentrations of perfluoroisobutene could be analyzed directly by manual split injection, sorbent sampling followed by thermal desorption GC/MS allowed lower concentrations to be analyzed. However, a significant degradation of perfluoroisobutene observed after thermal desorption analysis inspired the use of derivatization of perfluoroisobutene with 3,4‐dimercaptotoluene. The use of Tenax TA sorbent tubes spiked with 3,4‐dimercaptotoluene and trimethylamine in a molar ratio of 1:8 proved successful for the quantification of a unique perfluoroisobutene derivative, and the method was validated for atmospheres in the range of 0.13–152 ppb with a relative standard deviation of less than 20% and an accuracy of 90%. Although carbonyl fluoride was less stable than perfluoroisobutene, direct analysis was possible at high concentrations but the response was not linear. The 3,4‐dimercaptotoluene derivatization method developed was also applicable for quantification of carbonyl fluoride atmospheres.

Carbonyl fluoride gas adsorption and detection by the pristine and Ni-doped inorganic boron nitride nanoclusters

Density functional theory calculations were performed for investigating the effect of doping the Ni atom on the sensing capability of a B24N24 nanocluster ((BN)24) in detecting the carbonyl fluoride (CF) gas. We predicted that the interaction of pristine (BN)24 with CF was a physisorption, and the sensing response (SR) of (BN)24 was 5.1. The adsorption energy of CF changed from −4.9 to −21.4 kcal/mol after doping the Ni atom. Also, the corresponding SR increased significantly to 77.8, indicating that the Ni transition metal significantly increased the sensitivity of the nanocluster. It was shown that the Ni@(BN)24 may selectively detect the CF gas among O2, CF4, SiF4, C2F6, and HF gases. Our theoretical results further supported the fact that the metal@BN nano-structures have practical applications.

Directly purifiable Pre-oxidation of Spiro-OMeTAD for stability enhanced perovskite solar cells with efficiency over 23%

Spiro-OMeTAD so far remains the most popular material as the hole-transport layer (HTL) for efficient perovskite solar cells (PSCs). However, the residual dopant, by-products and the hygroscopic lithium salt that remained in the HTL are commonly harmful to the PSCs performance. We develop here a new approach to pre-oxidize the spiro-OMeTAD by using the Cobalt (III) trifluoride (CoF3) as a p-type dopant. Both the CoF3 and its reduced form (CoF2) are insoluble in the spiro-OMeTAD:LiTFSI mixture and the oxidation reaction occurs at the solid/liquid interface. Therefore, the unreacted dopant and by-products (CoF2) can be readily removed by filtering, leading to a purifiable pre-oxidation of spiro-OMeTAD and thus a high-quality HTL with improved conductivity and hole mobility. Additionally, part of detrimental Li+ ions can also be purified out of the spiro-OMeTAD solution in the form of LiF sediments, which improves the stability and reliability of the devices. The resulting PSC achieves an efficiency of 23.05% together with improved stability, maintaining 91% of its initial PCE after one month of storage in the atmosphere with 20–30% relative humidity. These findings provide a new strategy to dope HTL for efficient and stable PSCs.

Gas-Phase Chemistry of 1,1,2,3,3,4,4-Heptafluorobut-1-ene Initiated by Chlorine Atoms.

The possibility of mitigating climate change by switching to materials with low global warming potentials motivates a study of the spectroscopic and kinetic properties of a fluorinated olefin. The relative rate method was used to determine the rate constant for the reaction of heptafluorobut-1-ene (CF2=CFCF2CF2H) with chlorine atoms in air. A mercury UV lamp was used to generate atomic chlorine, which initiated chemistry monitored by FTIR spectroscopy. Ethane was used as the reference compound for kinetic studies. Oxidation of heptafluorobut-1-ene initiated by a chlorine atom creates carbonyl difluoride (CF2=O) and 2,2,3,3 tetrafluoropropanoyl fluoride (O=CFCF2CF2H) as the major products. Anharmonic frequency calculations allowing for several low-energy conformations of 1,1,2,3,3,4,4 heptafluorobut-1-ene and 2,2,3,3 tetrafluoropropanoyl fluoride, based on density functional theory, are in good accord with measurements. The global warming potentials of these two molecules were calculated from the measured IR spectra and estimated atmospheric lifetimes and found to be small, less than 1.

Carbon monoxide fluorination using alumina-supported cobalt trifluoride: a proof of concept

Carbonyl fluoride is a versatile compound commonly used in fluorine chemistry. Its conventional synthesis route is the fluorination of carbon monoxide with elemental fluorine. The formation of carbon tetrafluoride as a byproduct, reducing product purity, makes this route problematic. An alternative approach is presented here: the use of alumina-supported cobalt trifluoride in a packed-bed reactor. The cobalt trifluoride was prepared by wet impregnation of the alumina with cobalt nitrate, calcination to form the cobalt mixed oxide, and fluorination of the oxide with fluorine gas to form the cobalt trifluoride. The prepared cobalt trifluoride was then used to fluorinate carbon monoxide in a heated packed bed reactor. Inline FTIR analysis confirmed the formation of carbonyl fluoride with characteristic bands at 976, 1253, and 1928 cm−1 clearly visible. There was no band indicative of the presence of carbon tetrafluoride detectable at 1278 cm−1. It can, therefore, be concluded that relatively pure carbonyl fluoride can be produced using cobalt trifluoride as fluorinating agent.

Broad Scope and High-Yield Access to Unsymmetrical Acyclic [11 C]Ureas for Biomedical Imaging from [11 C]Carbonyl Difluoride.

Effective methods are needed for labelling acyclic ureas with carbon-11 (t1/2 =20.4 min) as potential radiotracers for biomedical imaging with positron emission tomography (PET). Herein, we describe the rapid and high-yield syntheses of unsymmetrical acyclic [11 C]ureas under mild conditions (room temperature and within 7 min) using no-carrier-added [11 C]carbonyl difluoride with aliphatic and aryl amines. This methodology is compatible with diverse functionality (e. g., hydroxy, carboxyl, amino, amido, or pyridyl) in the substrate amines. The labelling process proceeds through putative [11 C]carbamoyl fluorides and for primary amines through isolable [11 C]isocyanate intermediates. Unsymmetrical [11 C]ureas are produced with negligible amounts of unwanted symmetrical [11 C]urea byproducts. Moreover, the overall labelling method tolerates trace water and the generally moderate to excellent yields show good reproducibility. [11 C]Carbonyl difluoride shows exceptional promise for application to the synthesis of acyclic [11 C]ureas as new radiotracers for biomedical imaging with PET.

Comparison of Three Measurement Principles on Water Triple Oxygen Isotopologues

The widespread method for measuring Δ17O (17O-excess) is an offline CoF3 (Cobalt tri-fluoride) conversion of water to molecular oxygen with subsequent isotope determination by dual inlet mass spectrometry. High precisions for Δ17O measurements, using CoF3 water conversion, are so far only possible with off-line methods. Here we report on an improved and modified online continuous flow method intended for high precision triple oxygen isotope analysis. This method is improved by optimizing the reactor (site for conversion of H2O into oxygen through the chemical reaction) compositions, size of the fused silica capillary, flow regulator, and data treatment. Our modified online continuous method was further compared with the recently developed cavity ring down measurement principle. The precision is significantly better for the commercially available laser-based system than our current version of improved online CoF3 conversion method using mass spectrometry. Factors identified for limiting precision in our continuous flow system are: (i) compaction of the reactor with time that leads to the restriction of flow rate of carrier gas, (ii) the CoF3 treatment, (iii) the amount of CoF3 inside the reactor, (iv) the pore size of the steel frit, and (v) the metallic tube. Changes in all of these items as well as the dimension of the fused silica capillary, the positioning of the fused silica capillary in the open split, and the memory effect can also lead to a declining precision. These limiting factors for precision still provide us enough space for further improvement of our improved online method which will be worthwhile for the measurement of smaller aliquot samples as fluid inclusions for palaeoclimatic applications. With present improvement, multiple injections (n = 15 or even more) should be applied to obtain a precision better than 10 per meg for Δ17O. Furthermore, a comparison of the laser-based system with an improved conventional equilibration method has been made on precipitation samples originating from Jungfraujoch.

The catalytic effects of H2O, basic and acidic catalysts on the gas‐phase hydrolysis mechanism of carbonyl fluoride (CF2O)

AbstractThe carbonyl fluoride (CF2O) is one of the significant atmospheric molecules, and its hydrolysis reaction has been considered the most potential removal process in the earth's troposphere. In this article, the hydrolysis reaction of CF2O assisted by H2O, basic (NH3 and CH3NHCH3), and acidic (H2SO4, HCOOH, and CF3COOH) catalysts have theoretically investigated using quantum chemical methods. These catalysts significantly decrease the hydrolysis reaction of barrier height by 20.4–28.8 kcal mol−1. Here two H‐transfer mechanisms have been identified in these catalyzed hydrolytic reactions as asynchronous collaborative caused by base molecules and the synchronous collaborative led by H2O and acid molecules. In addition, the rate coefficient and relative rate of all catalytic reactions have calculated using conventional transition state theory (TST) over a temperature range of 280–320 K. The results show that H2SO4 has the best catalytic effect without considering the concentration of catalyst molecules in the atmosphere. On the contrary, a high concentration of HCOOH (10 ppbv) is dominant in the catalytic reaction when considered the concentrations of catalyst molecules. In this work, it was identified that the catalytic efficiencies of H2O, acid and base molecules upon addition reaction between CF2O and H2O is not only related to their catalytic mechanisms but also depending upon their concentrations in the atmosphere.