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Paulo Limão-vieira - One of the best experts on this subject based on the ideXlab platform.
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Electron Transfer Induced Decomposition in Potassium–Nitroimidazoles Collisions: An Experimental and Theoretical Work
International Journal of Molecular Sciences, 2019Co-Authors: M. Mendes, M.-c. Bacchus-montabonel, Gustavo García, Paulo Limão-vieiraAbstract:Electron transfer induced decomposition mechanism of nitroimidazole and a selection of analogue molecules in collisions with neutral Potassium (K) Atoms from 10 to 1000 eV have been thoroughly investigated. In this laboratory collision regime, the formation of negative ions was time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant anions have been assigned to the parent molecule and the nitrogen oxide anion (NO2–) and the electron transfer mechanisms are comprehensively discussed. This work focuses on the analysis of all fragment anions produced and it is complementary of our recent work on selective hydrogen loss from the transient negative ions produced in these collisions. Ab initio theoretical calculations were performed for 4-nitroimidazole (4NI), 2-nitroimidazole (2NI), 1-methyl-4- (Me4NI) and 1-methyl-5-nitroimidazole (Me5NI), and imidazole (IMI) in the presence of a Potassium Atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process.
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Ion-Pair Formation in Neutral Potassium-Neutral Pyrimidine Collisions: Electron Transfer Experiments
Frontiers in Chemistry, 2019Co-Authors: M. Mendes, S. Kumar, M.-c. Bacchus-montabonel, Gustavo García, Beatriz Pamplona, Filipe Ferreira Da Silva, Antonio Aguilar, Paulo Limão-vieiraAbstract:We report novel data on ion-pair formation in hyperthermal (30–800 eV) neutral Potassium collisions with neutral pyrimidine (Pyr, C4H4N2) molecules. In this collision regime, negative ions formed by electron transfer from the alkali Atom to the target molecule were time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant product anions have been assigned to CN− and C2H− and the electron transfer mechanisms are comprehensively discussed. Particular importance is also given to the efficient loss of integrity of the pyrimidine ring in the presence of an extra electron, which is in contrast to dissociative electron attachment experiments yielding the dehydrogenated parent anion. Theoretical calculations were performed for pyrimidine in the presence of a Potassium Atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process. In order to further our knowledge about the collision dynamics, Potassium cation (K+) energy loss spectrum has been obtained and within this context, we also discuss the role of the accessible electronic states. A vertical electron affinity of (−5.69 ± 0.20) eV was obtained and may be assigned to a π3*(b1) state that leads to CN− formation.
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Negative ion chemistry of Deoxyribose and THF upon Potassium Atom collisions
Journal of Physics: Conference Series, 2014Co-Authors: Diogo Almeida, F. Ferreira Da Silva, Gustavo García, Paulo Limão-vieiraAbstract:Negative ion formation in collisions of Potassium Atoms with tetrahydrofuran (THF) and D-Ribose (DR) were performed in a crossed molecular beam setup equipped with a time- of-flight (TOF) mass spectrometer. Owing to the role of these molecules as possible representations of the sugar unit in the DNA/RNA, the fragmentation patterns obtained for different collision energies were compared and the role of K+ post-collision interaction with the molecular is evaluated.
M.-c. Bacchus-montabonel - One of the best experts on this subject based on the ideXlab platform.
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Combined Experimental and Theoretical Studies on Electron Transfer in Potassium Collisions with CCl 4
Journal of Physical Chemistry A, 2020Co-Authors: K. Regeta, S. Kumar, T. Cunha, M. Mendes, A. Lozano, P. Pereira, G. Garcia, A. Moutinho, M.-c. Bacchus-montabonel, P. Limão-vieiraAbstract:Negative ion formation in electron transfer experiments from fast neutral Potassium (K) Atom collisions with neutral tetrachloromethane (CCl4) molecules has been investigated in the laboratory frame range of 8–1000 eV. Comprehensive calculations on the electronic structure were performed for CCl4 in the presence of a Potassium Atom and used to help analyze the lowest unoccupied molecular orbitals participating in the collision process. Additionally, K+ energy loss produced in the forward direction has served to further our knowledge on the electronic state spectroscopy of CCl4. A vertical electron affinity of −0.79 ± 0.20 eV has been obtained and assigned to a purely repulsive transition from CCl4 ground state to the 2T2 state of the temporary negative ion yielding Cl– formation. Other features in the energy loss spectrum were observed for the first time and related to Cl2–, CCl2–, and CCl3– formation. Special attention is also given to the unresolved feature corresponding to a positive electron affinity of 0.24 ± 0.2 eV, assigned to a vibrationally hot transition from CCl4 ground state into the triply degenerate 2T2 excited state of the negative ion. The combined time-of-flight mass spectrometry together with K+ energy loss data represents the most comprehensive assignment of the tetrachloromethane anion yields and the role of CCl4 electronic states in collision induced dissociation to date.
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Electron Transfer Induced Decomposition in Potassium–Nitroimidazoles Collisions: An Experimental and Theoretical Work
International Journal of Molecular Sciences, 2019Co-Authors: M. Mendes, M.-c. Bacchus-montabonel, Gustavo García, Paulo Limão-vieiraAbstract:Electron transfer induced decomposition mechanism of nitroimidazole and a selection of analogue molecules in collisions with neutral Potassium (K) Atoms from 10 to 1000 eV have been thoroughly investigated. In this laboratory collision regime, the formation of negative ions was time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant anions have been assigned to the parent molecule and the nitrogen oxide anion (NO2–) and the electron transfer mechanisms are comprehensively discussed. This work focuses on the analysis of all fragment anions produced and it is complementary of our recent work on selective hydrogen loss from the transient negative ions produced in these collisions. Ab initio theoretical calculations were performed for 4-nitroimidazole (4NI), 2-nitroimidazole (2NI), 1-methyl-4- (Me4NI) and 1-methyl-5-nitroimidazole (Me5NI), and imidazole (IMI) in the presence of a Potassium Atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process.
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Ion-Pair Formation in Neutral Potassium-Neutral Pyrimidine Collisions: Electron Transfer Experiments
Frontiers in Chemistry, 2019Co-Authors: M. Mendes, S. Kumar, M.-c. Bacchus-montabonel, Gustavo García, Beatriz Pamplona, Filipe Ferreira Da Silva, Antonio Aguilar, Paulo Limão-vieiraAbstract:We report novel data on ion-pair formation in hyperthermal (30–800 eV) neutral Potassium collisions with neutral pyrimidine (Pyr, C4H4N2) molecules. In this collision regime, negative ions formed by electron transfer from the alkali Atom to the target molecule were time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant product anions have been assigned to CN− and C2H− and the electron transfer mechanisms are comprehensively discussed. Particular importance is also given to the efficient loss of integrity of the pyrimidine ring in the presence of an extra electron, which is in contrast to dissociative electron attachment experiments yielding the dehydrogenated parent anion. Theoretical calculations were performed for pyrimidine in the presence of a Potassium Atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process. In order to further our knowledge about the collision dynamics, Potassium cation (K+) energy loss spectrum has been obtained and within this context, we also discuss the role of the accessible electronic states. A vertical electron affinity of (−5.69 ± 0.20) eV was obtained and may be assigned to a π3*(b1) state that leads to CN− formation.
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Electron transfer driven decomposition of adenine and selected analogs as probed by experimental and theoretical methods
Journal of Chemical Physics, 2018Co-Authors: T. Cunha, G. Garcia, M.-c. Bacchus-montabonel, M. Mendes, F. Ferreira Da Silva, S. Eden, P. Limão-vieiraAbstract:We report on a combined experimental and theoretical study of electron-transfer-induced decomposition of adenine (Ad) and a selection of analog molecules in collisions with Potassium (K) Atoms. Time-of-flight negative ion mass spectra have been obtained in a wide collision energy range (6–68 eV in the centre-of-mass frame), providing a comprehensive investigation of the fragmentation patterns of purine (Pu), adenine (Ad), 9-methyl adenine (9-mAd), 6-dimethyl adenine (6-dimAd), and 2-D adenine (2-DAd). Following our recent communication about selective hydrogen loss from the transient negative ions (TNIs) produced in these collisions [T. Cunha et al., J. Chem. Phys. 148, 021101 (2018)], this work focuses on the production of smaller fragment anions. In the low-energy part of the present range, several dissociation channels that are accessible in free electron attachment experiments are absent from the present mass spectra, notably NH2 loss from adenine and 9-methyl adenine. This can be understood in terms of a relatively long transit time of the K+ cation in the vicinity of the TNI tending to enhance the likelihood of intramolecular electron transfer. In this case, the excess energy can be redistributed through the available degrees of freedom inhibiting fragmentation pathways. Ab initio theoretical calculations were performed for 9-methyl adenine (9-mAd) and adenine (Ad) in the presence of a Potassium Atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process.
M. Mendes - One of the best experts on this subject based on the ideXlab platform.
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Combined Experimental and Theoretical Studies on Electron Transfer in Potassium Collisions with CCl 4
Journal of Physical Chemistry A, 2020Co-Authors: K. Regeta, S. Kumar, T. Cunha, M. Mendes, A. Lozano, P. Pereira, G. Garcia, A. Moutinho, M.-c. Bacchus-montabonel, P. Limão-vieiraAbstract:Negative ion formation in electron transfer experiments from fast neutral Potassium (K) Atom collisions with neutral tetrachloromethane (CCl4) molecules has been investigated in the laboratory frame range of 8–1000 eV. Comprehensive calculations on the electronic structure were performed for CCl4 in the presence of a Potassium Atom and used to help analyze the lowest unoccupied molecular orbitals participating in the collision process. Additionally, K+ energy loss produced in the forward direction has served to further our knowledge on the electronic state spectroscopy of CCl4. A vertical electron affinity of −0.79 ± 0.20 eV has been obtained and assigned to a purely repulsive transition from CCl4 ground state to the 2T2 state of the temporary negative ion yielding Cl– formation. Other features in the energy loss spectrum were observed for the first time and related to Cl2–, CCl2–, and CCl3– formation. Special attention is also given to the unresolved feature corresponding to a positive electron affinity of 0.24 ± 0.2 eV, assigned to a vibrationally hot transition from CCl4 ground state into the triply degenerate 2T2 excited state of the negative ion. The combined time-of-flight mass spectrometry together with K+ energy loss data represents the most comprehensive assignment of the tetrachloromethane anion yields and the role of CCl4 electronic states in collision induced dissociation to date.
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Electron Transfer Induced Decomposition in Potassium–Nitroimidazoles Collisions: An Experimental and Theoretical Work
International Journal of Molecular Sciences, 2019Co-Authors: M. Mendes, M.-c. Bacchus-montabonel, Gustavo García, Paulo Limão-vieiraAbstract:Electron transfer induced decomposition mechanism of nitroimidazole and a selection of analogue molecules in collisions with neutral Potassium (K) Atoms from 10 to 1000 eV have been thoroughly investigated. In this laboratory collision regime, the formation of negative ions was time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant anions have been assigned to the parent molecule and the nitrogen oxide anion (NO2–) and the electron transfer mechanisms are comprehensively discussed. This work focuses on the analysis of all fragment anions produced and it is complementary of our recent work on selective hydrogen loss from the transient negative ions produced in these collisions. Ab initio theoretical calculations were performed for 4-nitroimidazole (4NI), 2-nitroimidazole (2NI), 1-methyl-4- (Me4NI) and 1-methyl-5-nitroimidazole (Me5NI), and imidazole (IMI) in the presence of a Potassium Atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process.
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Ion-Pair Formation in Neutral Potassium-Neutral Pyrimidine Collisions: Electron Transfer Experiments
Frontiers in Chemistry, 2019Co-Authors: M. Mendes, S. Kumar, M.-c. Bacchus-montabonel, Gustavo García, Beatriz Pamplona, Filipe Ferreira Da Silva, Antonio Aguilar, Paulo Limão-vieiraAbstract:We report novel data on ion-pair formation in hyperthermal (30–800 eV) neutral Potassium collisions with neutral pyrimidine (Pyr, C4H4N2) molecules. In this collision regime, negative ions formed by electron transfer from the alkali Atom to the target molecule were time-of-flight mass analyzed and the fragmentation patterns and branching ratios have been obtained. The most abundant product anions have been assigned to CN− and C2H− and the electron transfer mechanisms are comprehensively discussed. Particular importance is also given to the efficient loss of integrity of the pyrimidine ring in the presence of an extra electron, which is in contrast to dissociative electron attachment experiments yielding the dehydrogenated parent anion. Theoretical calculations were performed for pyrimidine in the presence of a Potassium Atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process. In order to further our knowledge about the collision dynamics, Potassium cation (K+) energy loss spectrum has been obtained and within this context, we also discuss the role of the accessible electronic states. A vertical electron affinity of (−5.69 ± 0.20) eV was obtained and may be assigned to a π3*(b1) state that leads to CN− formation.
Tom Efthimiopoulos - One of the best experts on this subject based on the ideXlab platform.
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control of the emission channels energy flow in a nonlinear laser Potassium Atom interaction
Journal of Physics B, 2012Co-Authors: D Pentaris, N. Merlemis, Tom Efthimiopoulos, Andreas LyrasAbstract:A numerical study of the emissions of a four-level Potassium Atom excited either by a single pulse or by a pair of temporally separated pulses is presented. For a low-intensity single-pulse two-photon excitation (|4S1/2〉↔|6S1/2〉), parametric emissions along path-1 (|6S1/2〉↔|5P3/2〉↔|4S1/2〉) are generated while along path-2 (|6S1/2〉↔|4P3/2〉↔|4S1/2〉) are essentially inactive. But for high single-pulse excitation, the path-1 emissions saturate and delayed path-2 amplified spontaneous emissions appear. It is shown that in the case of a double-pulse excitation scheme, proper temporal separation of the pulses and saturation of path-1 emissions caused by the first pulse can be applied to selectively transfer the excitation energy from path-1 to path-2 emissions.
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Control of the emission channels energy flow in a nonlinear laser–Potassium Atom interaction
Journal of Physics B: Atomic Molecular and Optical Physics, 2012Co-Authors: D Pentaris, N. Merlemis, Tom Efthimiopoulos, Andreas LyrasAbstract:A numerical study of the emissions of a four-level Potassium Atom excited either by a single pulse or by a pair of temporally separated pulses is presented. For a low-intensity single-pulse two-photon excitation (|4S1/2〉↔|6S1/2〉), parametric emissions along path-1 (|6S1/2〉↔|5P3/2〉↔|4S1/2〉) are generated while along path-2 (|6S1/2〉↔|4P3/2〉↔|4S1/2〉) are essentially inactive. But for high single-pulse excitation, the path-1 emissions saturate and delayed path-2 amplified spontaneous emissions appear. It is shown that in the case of a double-pulse excitation scheme, proper temporal separation of the pulses and saturation of path-1 emissions caused by the first pulse can be applied to selectively transfer the excitation energy from path-1 to path-2 emissions.
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Temporal dynamics of the internally generated radiations in a two-photon excited four-level Potassium Atom
Journal of Modern Optics, 2012Co-Authors: D Pentaris, N. Merlemis, Tom Efthimiopoulos, Andreas LyrasAbstract:A numerical study, stimulated by existing experimental results concerning the temporal dynamics of internally generated radiations, is presented for a four-level system of the Potassium Atom. An intense nanosecond duration laser pulse excites the two-photon transition and initiates the generation of internal radiations from quantum noise. It is shown that the temporal profiles of the generated radiations along the Atomic path-1, ( ) and path-2, ( ), evolve differently as a function of certain system parameters. It is also shown that the excitation laser intensity affects the parametric emissions along path-1 and the population of the states. The path-2 emissions, which also depend on the excitation laser intensity, are most probably due to amplified spontaneous emission (ASE), without population inversion, in the case of strong excitation. We finally examine the radiation dynamics under the effect of the elastic dephasing collisions between the Potassium Atoms with the buffer gas a...
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Saturation and population transfer of a two-photon excited four-level Potassium Atom
Journal of Physics B: Atomic Molecular and Optical Physics, 2011Co-Authors: A. Armyras, N. Merlemis, Tom Efthimiopoulos, D Pentaris, Andreas LyrasAbstract:A theoretical study of the nonlinearity reduction in a four-level system of a Potassium Atom in the presence of a strong nanosecond laser field, which excites the transition |4S1/2↔|6S1/2 with two photons, is presented. It is shown that the destructive quantum interference between the laser field and the internally generated radiations results in a linear response of the Atomic path-1 (|4S1/2↔|6S1/2↔|5P3/2↔|4S1/2) emitted parametric fields. For sufficiently high laser intensities and/or Atomic densities, the path-1 emitted fields are driven into saturation, a regime accompanied by a substantial population redistribution among the states. Reasonable agreement between earlier experimental results and the theoretical ones is obtained. It is also shown that upon saturation of path-1, for low Atomic density, the path-2 (|4S1/2↔|6S1/2↔|4P3/2↔|4S1/2) is activated. A subtle interplay between laser intensity and Atomic density may determine the activation of path-2. Also, it is shown that the path-2 emission |6S1/2↔|4P3/2 is an amplified spontaneous emission process which induces a |4P3/2↔|4S1/2 emission, without population inversion, in a cascade scheme.
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Stimulated emissions and quantum interference in Potassium Atom-laser interaction
Journal of Physics B: Atomic Molecular and Optical Physics, 2003Co-Authors: N. Merlemis, M. Katharakis, Emmanuel Koudoumas, Tom EfthimiopoulosAbstract:The interaction of a laser with Potassium Atoms is investigated by monitoring the radiation of the 5P–4S transition under the two-photon 4S1/2 –6S1/2 excitation. For low number density and laser intensity the observed radiation is parametric axial or conical, depending on the laser detuning from the two-photon resonance, the number density and the laser intensity. With increasing laser intensities and number densities, an additional delayed component is observed corresponding to a two-step four-wave mixing with the participation of internally generated photons. A two-photon quantum interference effect is observed for the total (axial and conical) parametric four-wave mixing emission. A deviation from the proposed model under certain experimental parameters is attributed to a two-step four-wave mixing and the phase mismatch of the parametric processes.
P. Limão-vieira - One of the best experts on this subject based on the ideXlab platform.
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Combined Experimental and Theoretical Studies on Electron Transfer in Potassium Collisions with CCl 4
Journal of Physical Chemistry A, 2020Co-Authors: K. Regeta, S. Kumar, T. Cunha, M. Mendes, A. Lozano, P. Pereira, G. Garcia, A. Moutinho, M.-c. Bacchus-montabonel, P. Limão-vieiraAbstract:Negative ion formation in electron transfer experiments from fast neutral Potassium (K) Atom collisions with neutral tetrachloromethane (CCl4) molecules has been investigated in the laboratory frame range of 8–1000 eV. Comprehensive calculations on the electronic structure were performed for CCl4 in the presence of a Potassium Atom and used to help analyze the lowest unoccupied molecular orbitals participating in the collision process. Additionally, K+ energy loss produced in the forward direction has served to further our knowledge on the electronic state spectroscopy of CCl4. A vertical electron affinity of −0.79 ± 0.20 eV has been obtained and assigned to a purely repulsive transition from CCl4 ground state to the 2T2 state of the temporary negative ion yielding Cl– formation. Other features in the energy loss spectrum were observed for the first time and related to Cl2–, CCl2–, and CCl3– formation. Special attention is also given to the unresolved feature corresponding to a positive electron affinity of 0.24 ± 0.2 eV, assigned to a vibrationally hot transition from CCl4 ground state into the triply degenerate 2T2 excited state of the negative ion. The combined time-of-flight mass spectrometry together with K+ energy loss data represents the most comprehensive assignment of the tetrachloromethane anion yields and the role of CCl4 electronic states in collision induced dissociation to date.
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Electron transfer driven decomposition of adenine and selected analogs as probed by experimental and theoretical methods
Journal of Chemical Physics, 2018Co-Authors: T. Cunha, G. Garcia, M.-c. Bacchus-montabonel, M. Mendes, F. Ferreira Da Silva, S. Eden, P. Limão-vieiraAbstract:We report on a combined experimental and theoretical study of electron-transfer-induced decomposition of adenine (Ad) and a selection of analog molecules in collisions with Potassium (K) Atoms. Time-of-flight negative ion mass spectra have been obtained in a wide collision energy range (6–68 eV in the centre-of-mass frame), providing a comprehensive investigation of the fragmentation patterns of purine (Pu), adenine (Ad), 9-methyl adenine (9-mAd), 6-dimethyl adenine (6-dimAd), and 2-D adenine (2-DAd). Following our recent communication about selective hydrogen loss from the transient negative ions (TNIs) produced in these collisions [T. Cunha et al., J. Chem. Phys. 148, 021101 (2018)], this work focuses on the production of smaller fragment anions. In the low-energy part of the present range, several dissociation channels that are accessible in free electron attachment experiments are absent from the present mass spectra, notably NH2 loss from adenine and 9-methyl adenine. This can be understood in terms of a relatively long transit time of the K+ cation in the vicinity of the TNI tending to enhance the likelihood of intramolecular electron transfer. In this case, the excess energy can be redistributed through the available degrees of freedom inhibiting fragmentation pathways. Ab initio theoretical calculations were performed for 9-methyl adenine (9-mAd) and adenine (Ad) in the presence of a Potassium Atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process.