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Ovad T, Sapunar M, Sršeň Š, Slavíček P, Mašín Z, Jones NC, Hoffmann SV, Ranković M, Fedor J. Excitation and fragmentation of the dielectric gas C 4F 7N: Electrons vs photons. J Chem Phys 2023; 158:014303. [PMID: 36610949 DOI: 10.1063/5.0130216] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
C4F7N is a promising candidate for the replacement of sulfur hexafluoride as an insulating medium, and it is important to understand the chemical changes initiated in the molecule by collision with free electrons, specifically the formation of neutral fragments. The first step of neutral fragmentation is electronic excitation, yet neither the absorption spectrum in the vacuum ultraviolet (VUV) region nor the electron energy loss spectrum have previously been reported. Here, we experimentally probed the excited states by VUV photoabsorption spectroscopy and electron energy loss spectroscopy (EELS). We found that the distribution of states populated upon electron impact with low-energy electrons is significantly different from that following photoabsorption. This difference was confirmed and interpreted with ab initio modeling of both VUV and EELS spectra. We propose here a new computational protocol for the simulation of EELS spectra combining the Born approximation with approximate forms of correlated wave functions, which allows us to calculate the (usually very expensive) scattering cross sections at a cost similar to the calculation of oscillator strengths. Finally, we perform semi-classical non-adiabatic dynamics simulations to investigate the possible neutral fragments of the molecule formed through electron-induced neutral dissociation. We show that the product distribution is highly non-statistical.
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Affiliation(s)
- Tomáš Ovad
- Department of Physical Chemistry, University of Chemistry and Technology, Technická 5, Prague 6, Czech Republic
| | - Marin Sapunar
- Department of Physical Chemistry, University of Chemistry and Technology, Technická 5, Prague 6, Czech Republic
| | - Štěpán Sršeň
- Department of Physical Chemistry, University of Chemistry and Technology, Technická 5, Prague 6, Czech Republic
| | - Petr Slavíček
- Department of Physical Chemistry, University of Chemistry and Technology, Technická 5, Prague 6, Czech Republic
| | - Zdeněk Mašín
- Faculty of Mathematics and Physics, Charles University, Institute of Theoretical Physics, V Holešovičkách 2, 18000 Prague, Czech Republic
| | - Nykola C Jones
- ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
| | - Søren Vrønning Hoffmann
- ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
| | - Miloš Ranković
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague 8, Czech Republic
| | - Juraj Fedor
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague 8, Czech Republic
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2
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Pereira-da-Silva J, Rodrigues R, Ramos J, Brígido C, Botnari A, Silvestre M, Ameixa J, Mendes M, Zappa F, Mullock SJ, Araújo JMM, Varella MTDN, Cornetta LM, da Silva FF. Electron Driven Reactions in Tetrafluoroethane: Positive and Negative Ion Formation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2021; 32:1459-1468. [PMID: 33998788 DOI: 10.1021/jasms.1c00057] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
In the search for alternatives to chlorine-containing gases, tetrafluoroethane, CF3CH2F (R134a), a widely used refrigerant gas, has been recognized as a promising substitute for dichlorodifluoromethane, CCl2F2 (R12). When R12 is replaced by R134a, the global warming potential drops from 8100 to 1430, the ozone depletion potential changes from 1 to 0, and the atmospheric lifetime decreases from 100 to 14 years. Electron interactions in the gas phase play a fundamental role in the atmospheric sciences. Here, we present a detailed study on electron-driven fragmentation pathways of CF3CH2F, in which we have investigated processes induced by both electron ionization and electron attachment. The measurements allow us to report the ion efficiency curves for ion formation in the energy range of 0 up to 25 eV. For positive ion formation, R134a dissociates into a wide assortment of ions, in which CF3+ is observed as the most abundant out of seven ions with a relative intensity above 2%. The results are supported by quantum chemical calculations based on bound state techniques, electron-impact ionization models, and electron-molecule scattering simulations, showing a good agreement. Moreover, the experimental first ionization potential was found at 13.10 ± 0.17 eV and the second at around 14.25 eV. For negative ion formation, C2F3- was detected as the only anion formed, above 8.3 eV. This study demonstrates the role of electrons in the dissociation of R134a, which is relevant for an improvement of the refrigeration processes as well as in atmospheric chemistry and plasma sciences.
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Affiliation(s)
- João Pereira-da-Silva
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - Rodrigo Rodrigues
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - João Ramos
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - Carlos Brígido
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - Alexandru Botnari
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - Miguel Silvestre
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - João Ameixa
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - Mónica Mendes
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - Fábio Zappa
- Departamento de Física-ICE, Universidade Federal de Juiz de Fora, Campus Universitário, 36036-900 Juiz de Fora, MG, Brazil
| | - Stephen J Mullock
- Kore Technology Ltd., Cambridge Science Park, Cambridge CB4 4WF, U.K
| | - João M M Araújo
- LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
| | - Márcio T do N Varella
- Instituto de Física, Universidade de São Paulo, Rua do Matão 1371, 05508-090 São Paulo, Brazil
| | - Lucas M Cornetta
- Instituto de Física Gleb Wataghin da Universidade Estadual de Campinas, 13083-859 Campinas, Brazil
| | - Filipe Ferreira da Silva
- CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal
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Chen Y, Yu T, Wu X, Zhou X, Liu S, Liu F, Dai X. C–F and C–H bond cleavage mechanisms of trifluoromethane ions in low-lying electronic states: threshold photoelectron–photoion coincidence imaging and theoretical investigations. Phys Chem Chem Phys 2020; 22:13808-13817. [DOI: 10.1039/d0cp01793k] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Dissociative ionization of trifluoromethane (CHF3) is investigated in the 13.9–18.0 eV energy range using the threshold photoelectron–photoion coincidence (TPEPICO) technique coupled to a vacuum ultraviolet synchrotron radiation source.
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Affiliation(s)
- Yan Chen
- National Institute of Metrology
- Beijing 100013
- China
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
| | - Tongpo Yu
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Xiangkun Wu
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Xiaoguo Zhou
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Shilin Liu
- Hefei National Laboratory for Physical Sciences at the Microscale
- Department of Chemical Physics
- University of Science and Technology of China
- Hefei 230026
- China
| | - Fuyi Liu
- National Synchrotron Radiation Laboratory
- University of Science and Technology of China
- Hefei 230029
- China
| | - Xinhua Dai
- National Institute of Metrology
- Beijing 100013
- China
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Kundu S, Prabhudesai VS, Krishnakumar E. Electron induced reactions in condensed mixtures of methane and ammonia. Phys Chem Chem Phys 2017; 19:25723-25733. [PMID: 28913527 DOI: 10.1039/c7cp04490a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We demonstrate the efficient formation of carbon-nitrogen bonds starting from CH4 and NH3 on a metal surface at cryogenic temperatures. Electrons in the energy range of 1-90 eV are used to initiate chemical reactions in mixed molecular films of CH4 and NH3 at ∼15 K, and the products are detected by performing temperature programmed desorption (TPD). Extensive dehydrogenation occurs at all energies giving the products CH2NH and HCN in preference to CH3NH2. This is likely to do with the energetics of the reactions and the subsequent stability of these species in the condensed film. Thermal processing of the irradiated mixture favours dehydrogenation as indicated by the results of using different desorption rates. Electron impact excitation and subsequent dissociation into radicals is the reaction-initiating step rather than ionization of CH4 and NH3, as inferred from the yield of products as a function of electron energy. This could give insight into the important catalytic process of the industrial scale synthesis of HCN from CH4 and NH3 over Pt. This may also be a relevant pathway in the astrochemical environment where CN and HCN are abundant and low-energy electrons are found ubiquitously.
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Affiliation(s)
- Sramana Kundu
- Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Colaba, Mumbai-400005, India.
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5
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Karwasz G, Fedus K. Some Systematics in Electron Scattering Cross Sections. FUSION SCIENCE AND TECHNOLOGY 2017. [DOI: 10.13182/fst13-a16440] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Grzegorz Karwasz
- Nicolaus Copernicus University, Institute of Physics Grudziadzka 507, 87-100 Torun, Poland
| | - Kamil Fedus
- Nicolaus Copernicus University, Institute of Physics Grudziadzka 507, 87-100 Torun, Poland
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