Tropospheric degradation of propanethiol initiated by Cl radicals: Kinetics, mechanism and computational studies

The rate coefficient for the reaction of Cl radicals with n-propanethiol has been determined at 298 K and atmospheric pressure to be: (2.37 ± 0.66) × 10−10 cm3 molecule−1 s−1. Dipropyl disulfide, sulfur dioxide, and propionaldehyde, were observed as main reaction products. The yield of formation of dipropyl disulfide was quantified. Potential energy surfaces and thermodynamic data at 298 K were calculated for the gauche and trans conformers of n-propanethiol using the CBS-QB3, M06-D3/cc-pVTZ and M06-2X/cc-pVTZ levels of theory. We concluded that the formation of the prereactive complex in which chlorine is ‘bound’ to the sulfur atom is the decisive step in the reaction paths.Fil: Ladino Cardona, Miyer Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Blanco, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Ventura, Oscar N.. Universidad de la República Facultad de Química; UruguayFil: Teruel, Mariano Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Mechanistic study of the complex photooxidation of allyl methyl sulfide (AMS): reaction paths and products of addition under different atmospheric conditions

The addition mechanism of the OH-initiated oxidation of allyl methyl sulfide (AMS) under atmospheric conditions was studied theoretically using both density functional theory (DFT) and the SVECV-f12 composite method. We found that the addition does not occur directly but rather through a pre-reactive complex that serves as a previous stage for addition at both the C1 and C2 positions. However, based on thermodynamics the addition at C2 possibly occurs by branching of the C1 addition mechanism. Once the addition proceeds, the reaction with O2 under atmospheric conditions produces RO2 radicals that can decompose in multiple ways. Complex mechanisms of intramolecular rearrangement and decomposition both in the absence and presence of NOx have been examined. The thermodynamically most favourable decomposition paths produce 2-hydroxy-acetaldehyde, 2-methyl-thio-acetaldehyde, formaldehyde, and the methyl thiomethyl peroxy (MSP) intermediate. This latter species is proposed as the main source of sulfur dioxide (SO2), which is the product found in the highest yield during the experimental determinations.Fil: Ladino Cardona, Miyer Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Blanco, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Teruel, Mariano Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Ventura, Oscar N.. Universidad de la República; Urugua

Gas phase degradation of trifluoromethyl peroxynitrate and trifluoromethyl nitrate in presence of water vapour

Trifluoromethyl peroxynitrate (CF3O2NO2) and trifluoromethyl nitrate (CF3ONO2) could be formed in the degradation of chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons and hydrofluoroethers, from the reaction of CF3Ox radicals and NO2. In the present work, the role of gas-phase water in the degradation of CF3O2NO2 and CF3ONO2 was evaluated for the first time. The study has included experiments with and without water, theoretical calculation and kinetics mechanism modelling. Concentration of fluorinated species in different experimental systems He, He/H2O, N2, and N2/H2O were monitored by infrared spectroscopy. Results indicated that water vapour does not affect the peroxynitrate stability. On the other hand, nitrate degrades quickly in presence of water forming HNO3, CF2O and HF, while, in absence of water, the products are NO2 and CF2O. Kinetics mechanism was proposed and modelled to corroborate the experimental results. Theoretical calculations show that the formation of Van der Waals complexes CF3O2NO2·(H2O)n, CF3ONO2·(H2O)n is unfavourable. Mechanism for CF3ONO2 degradation in the presence and absence of water are discussed.Fil: Salas, Juana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Ladino Cardona, Miyer Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Burgos Paci, Maximiliano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Malanca, Fabio Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Probing the pyrolysis of methyl formate in the dilute gas phase by synchrotron radiation and theory

The thermal dissociation of the atmospheric constituent methyl formate was probed by coupling pyrolysis with imaging photoelectron photoion coincidence spectroscopy (iPEPICO) using synchrotron VUV radiation at the Swiss Light Source (SLS). iPEPICO allows threshold photoelectron spectra to be obtained for pyrolysis products, distinguishing isomers and separating ionic and neutral dissociation pathways. In this work, the pyrolysis products of dilute methyl formate, CH3OC(O)H, were elucidated to be CH3OH + CO, 2 CH2O and CH4 + CO2 as in part distinct from the dissociation of the radical cation (CH3OH+• + CO and CH2OH+ + HCO). Density functional theory, CCSD(T), and CBS-QB3 calculations were used to describe the experimentally observed reaction mechanisms, and the thermal decomposition kinetics and the competition between the reaction channels are addressed in a statistical model. One result of the theoretical model is that CH2O formation was predicted to come directly from methyl formate at temperatures below 1200 K, while above 1800 K, it is formed primarily from the thermal decomposition of methanol.Fil: Lowe, Bethany. University of Ottawa; CanadáFil: Ladino Cardona, Miyer Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Salas, Juana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Bodi, Andras. Paul Scherrer Institute; SuizaFil: Burgos Paci, Maximiliano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Mayer, Paul. University of Ottawa; Canad

Pyrolysis of Trifluoroacetic Acid and Trifluoroacetic Anhydride Studied with Mass Spectrometry and Synchrotron Radiation: Decomposition and Free Radical Formation

The remediation strategies for accumulated polyfluoroalkyl substances (PFAS) are a subject of great concern in environmental science. In this study, the thermal decomposition of trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAN), taken as models of PFAS, were explored. Imaging photoelectron photoion coincidence (iPEPICO) spectroscopy was used to detect pyrolysis products from room temperature to 1000 °C under dilute conditions. The observed pyrolysis products of each molecule were CO, CO2, CF2, and CF2O (and CF3 for TFAN), with some species reflecting unimolecular rearrangement prior to dissociation. Electronic structure calculations using density functional theory and the SVECV-F12 composite method were employed to evaluate the energy of the different decomposition channels. The results show the advantage of exploring the pyrolysis under dilute conditions to catch the first stages of unimolecular dissociation of these molecules for the first time.Fil: Ladino Cardona, Miyer Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Salas, Juana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Lesniak, Lukas. University of Ottawa; CanadáFil: Mommers, A. A.. University of Ottawa; CanadáFil: Mayer, Paul M.. University of Ottawa; CanadáFil: Burgos Paci, Maximiliano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Degradation mechanism of 2-fluoropropene by Cl atoms: Experimental and theoretical products distribution studies

The gas-phase reaction products of 2-fluoropropene (2FP) with Cl atoms have been determined for the first time at 298 K and atmospheric pressure using a 1080 L quartz-glass photoreactor coupled with in situ FTIR spectroscopy to monitor reactants and products. Acetyl fluoride and formyl chloride were observed as the main products with yields of (106 ± 10)% and (100 ± 11)%, respectively. Electronic structure calculations of reactants, intermediates, products and transition states on a detailed mechanism of the reaction were performed by DFT procedures (BMK, M06, M062X/D3), as well as accurate composite methods on both the addition and abstraction reaction channels. From the joint experimental and theoretical studies, we concluded that the reaction occurs primarily via addition to the Cα carbon, with a smaller participation of the addition on the Cβ carbon, which is not produced directly from the separated reactants but from the CH3CFCH2Cl intermediate radical through a submerged transition state. The abstraction channel occurs at larger energies than the addition ones, and also presents a submerged transition state, with a lower barrier. No products arising from this channel are expected. The proposed mechanism explains also why formaldehyde, predicted as a product by former theoretical studies, is not found among the experimental products. The atmospheric implications of the reaction products are assessed. This journal isFil: Rivela Fretes, Cynthia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Ladino Cardona, Miyer Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Blanco, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Barnes, Tamara Eliana. Wuppertal Institut Für Klima, Umwelt, Energie Ggmbh.; AlemaniaFil: Kieninger, Martina. Universidad de la República Facultad de Química; UruguayFil: Ventura, Oscar N.. Universidad de la República Facultad de Química; UruguayFil: Teruel, Mariano Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Kinetics, product distribution and atmospheric implications of the gas-phase oxidation of allyl sulfides by OH radicals

Relative rate coefficients of the OH radical -initiated oxidation of allyl methyl sulfide (AMS, H2C[dbnd]CHCH2SCH3) and allyl ethyl sulfide (AES, H2C[dbnd]CHCH2SCH2CH3) have been measured at atmospheric pressure of synthetic air and 298 K: kAMS= (4.98 ± 1.42) and kAES= (6.88 ± 1.49) × 10−11 cm3 molecule−1 s−1 by means of in situ FTIR spectroscopy. In addition, the molar yields of the main reaction products of AMS with OH radicals formed in the absence and presence of nitric oxides (NOX) were determined to be the following: sulfur dioxide (95 ± 12) % and (51 ± 12) % for acrolein (50 ± 9) % and (41 ± 9) %. In the reaction of AES with OH radicals, the following molar yields were obtained: for sulfur dioxide (88 ± 13) % and (56 ± 12) % for acrolein (36 ± 9) % and (41 ± 9) %. The present results suggest that the abstraction at C3 plays an important role in the oxidation mechanism as the addition to the double bond. This work represents the first study of the OH radical interaction with AMS and AES carried out under atmospheric conditions. The atmospheric implications were discussed in terms of the atmospheric residence times of the sulfur-containing compounds studied and the products formed in the presence and absence of NOx. SO2 formation seems to be the main fate of the gas-phase allyl sulfides oxidation with significant acidifying potentials and short-chain aldehydes production like formaldehyde and acetaldehyde.Fil: Ladino Cardona, Miyer Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Gibilisco, Rodrigo Gastón. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Química del Noroeste. Universidad Nacional de Tucumán. Facultad de Bioquímica, Química y Farmacia. Instituto de Química del Noroeste; ArgentinaFil: Rivela Fretes, Cynthia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Blanco, Maria Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Patroescu Klotz, Iulia. Physikalische Chemie, Bergische Universität Wuppertal,; AlemaniaFil: Illmann, Niklas. Physikalische Chemie, Bergische Universität Wuppertal,; AlemaniaFil: Wiesen, Peter. Physikalische Chemie, Bergische Universität Wuppertal,; AlemaniaFil: Teruel, Mariano Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin