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Falkowski AG, da Costa RF, Lima MAP, de A Cadena A, Pocoroba R, Jones R, Mathur M, Childers JG, Khakoo MA, Kossoski F. Electron impact electronic excitation of benzene: Theory and experiment. J Chem Phys 2023; 159:194301. [PMID: 37966005 DOI: 10.1063/5.0173024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2023] [Accepted: 10/03/2023] [Indexed: 11/16/2023] Open
Abstract
We report experimental differential cross sections (DCSs) for electron impact excitation of bands I to V of benzene at incident energies of 10, 12.5, 15, and 20 eV. They are compared to calculations using the Schwinger multichannel method while accounting for up to 437 open channels. For intermediate scattering angles, the calculations reveal that the most intense band (V) emerges from surprisingly similar contributions from all its underlying states (despite some preference for the dipole-allowed transitions). They further shed light on intricate multichannel couplings between the states of bands I to V and higher-lying Rydberg states. In turn, the measurements support a vibronic coupling mechanism for excitation of bands II and IV and also show an unexpected forward peak in the spin-forbidden transition accounting for band III. Overall, there is decent agreement between theory and experiment at intermediate angles and at lower energies and in terms of the relative DCSs of the five bands. Discrepancies between the present and previous experiment regarding bands IV and V draw attention to the need of additional experimental investigations. We also report measured DCSs for vibrational excitation of combined C-H stretching modes.
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Affiliation(s)
- Alan G Falkowski
- Instituto de Física "Gleb Wataghin," Universidade Estadual de Campinas, Campinas, Brazil
| | - Romarly F da Costa
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-580 Santo André, São Paulo, Brazil
| | - Marco A P Lima
- Instituto de Física "Gleb Wataghin," Universidade Estadual de Campinas, Campinas, Brazil
| | - Alexi de A Cadena
- Physics Department, California State University, Fullerton, California 92831, USA
| | - Ronald Pocoroba
- Physics Department, California State University, Fullerton, California 92831, USA
| | - Regan Jones
- Physics Department, California State University, Fullerton, California 92831, USA
| | - Mahak Mathur
- Troy High School, 2200 Dorothy Lane, Fullerton, California 92831, USA
| | - J G Childers
- Physics Department, California State University, Fullerton, California 92831, USA
| | - Murtadha A Khakoo
- Physics Department, California State University, Fullerton, California 92831, USA
| | - Fábris Kossoski
- Laboratoire de Chimie et Physique Quantiques (UMR 5626), Université de Toulouse, CNRS, UPS, 31062 Toulouse, France
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2
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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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Thodika M, Matsika S. Projected Complex Absorbing Potential Multireference Configuration Interaction Approach for Shape and Feshbach Resonances. J Chem Theory Comput 2022; 18:3377-3390. [PMID: 35622933 DOI: 10.1021/acs.jctc.1c01310] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Anion resonances are formed as metastable intermediates in low-energy electron-induced reactions. Due to the finite lifetimes of resonances, applying standard Hermitian formalism for their characterization presents a vexing problem for computational chemists. Numerous modifications to conventional quantum chemical methods have enabled satisfactory characterization of resonances, but specific issues remain, especially in describing two-particle one-hole (2p-1h) resonances. An accurate description of these resonances and their coupling with single-particle resonances requires a multireference approach. We propose a projected complex absorbing potential (CAP) implementation within the multireference configuration interaction (MRCI) framework to characterize single-particle and 2p-1h resonances. As a first application, we use the projected-CAP-MRCI approach to characterize and benchmark the 2Πg shape resonance in N2-. We test its performance as a function of the size of the subspace and other parameters, and we compute the complex potential energy surface of the 2Πg shape resonance to show that a smooth curve is obtained. One key benefit of MRCI is that it can describe Feshbach resonances (most common examples of 2p-1h resonances) at the same footing as shape resonances. Therefore, it is uniquely positioned to describe mixing between the different channels. To test these additional capabilities, we compute Feshbach resonances in H2O- and anions of dicyanoethylene isomers. We find that CAP-MRCI can efficiently capture the mixing between the Feshbach and shape resonances in dicyanoethylene isomers, which has significant consequences for their lifetimes.
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Affiliation(s)
- Mushir Thodika
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, United States
| | - Spiridoula Matsika
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, United States
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Mendes M, Pamplona B, Kumar S, da Silva FF, Aguilar A, García G, Bacchus-Montabonel MC, Limao-Vieira P. Ion-Pair Formation in Neutral Potassium-Neutral Pyrimidine Collisions: Electron Transfer Experiments. Front Chem 2019; 7:264. [PMID: 31058139 PMCID: PMC6482480 DOI: 10.3389/fchem.2019.00264] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2019] [Accepted: 04/01/2019] [Indexed: 11/13/2022] Open
Abstract
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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Affiliation(s)
- Mónica Mendes
- Atomic and Molecular Collisions Laboratory, Centre of Physics and Technological Research (CEFITEC), Department of Physics, Universidade NOVA de Lisboa, Costa de Caparica, Portugal.,Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - Beatriz Pamplona
- Atomic and Molecular Collisions Laboratory, Centre of Physics and Technological Research (CEFITEC), Department of Physics, Universidade NOVA de Lisboa, Costa de Caparica, Portugal
| | - Sarvesh Kumar
- Atomic and Molecular Collisions Laboratory, Centre of Physics and Technological Research (CEFITEC), Department of Physics, Universidade NOVA de Lisboa, Costa de Caparica, Portugal
| | - Filipe Ferreira da Silva
- Atomic and Molecular Collisions Laboratory, Centre of Physics and Technological Research (CEFITEC), Department of Physics, Universidade NOVA de Lisboa, Costa de Caparica, Portugal
| | - Antonio Aguilar
- Departament de Ciència de Materials i Química Física, Universitat de Barcelona, Barcelona, Spain
| | - Gustavo García
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | | | - Paulo Limao-Vieira
- Atomic and Molecular Collisions Laboratory, Centre of Physics and Technological Research (CEFITEC), Department of Physics, Universidade NOVA de Lisboa, Costa de Caparica, Portugal
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Li Z, Ryszka M, Dawley MM, Carmichael I, Bravaya KB, Ptasińska S. Dipole-Supported Electronic Resonances Mediate Electron-Induced Amide Bond Cleavage. PHYSICAL REVIEW LETTERS 2019; 122:073002. [PMID: 30848645 DOI: 10.1103/physrevlett.122.073002] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2018] [Revised: 10/11/2018] [Indexed: 05/28/2023]
Abstract
Dissociative electron attachment (DEA) plays a key role in radiation damage of biomolecules under high-energy radiation conditions. The initial step in DEA is often rationalized in terms of resonant electron capture into one of the metastable valence states of a molecule followed by its fragmentation. Our combined theoretical and experimental investigations indicate that the manifold of states responsible for electron capture in the DEA process can be dominated by core-excited (shake-up) dipole-supported resonances. Specifically, we present the results of experimental and computational studies of the gas-phase DEA to three prototypical peptide molecules, formamide, N-methylformamide (NMF), and N,N-dimethyl-formamide (DMF). In contrast to the case of electron capture by positively charged peptides in which amide bond rupture is rare compared to N─C_{α} bond cleavage, fragmentation of the amide bond was observed in each of these three molecules. The ion yield curves for ions resulting from this amide bond cleavage, such as NH_{2}^{-} for formamide, NHCH_{3}^{-} for NMF, and N(CH_{3})_{2}^{-} for DMF, showed a double-peak structure in the region between 5 and 8 eV. The peaks are assigned to Feshbach resonances including core-excited dipole-supported resonances populated upon electron attachment based on high-level electronic structure calculations. Moreover, the lower energy peak is attributed to formation of the core-excited resonance that correlates with the triplet state of the neutral molecule. The latter process highlights the role of optically spin-forbidden transitions promoted by electron impact in the DEA process.
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Affiliation(s)
- Zhou Li
- Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA
- Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Michal Ryszka
- Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - M Michele Dawley
- Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Ian Carmichael
- Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA
| | - Ksenia B Bravaya
- Department of Chemistry, Boston University, Boston, Massachusetts 02215, USA
| | - Sylwia Ptasińska
- Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, USA
- Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA
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Loupas A, Lozano AI, Blanco F, Gorfinkiel JD, García G. Cross sections for electron scattering from thiophene for a broad energy range. J Chem Phys 2018; 149:034304. [DOI: 10.1063/1.5040352] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Alexandra Loupas
- Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus de Caparica, 2829-516 Lisbon, Portugal
- School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
| | - Ana. I. Lozano
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas, Serrano 113-bis, 28006 Madrid, Spain
| | - Francisco Blanco
- Departamento de Física Atómica, Molecular y Nuclear, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain
| | - Jimena D. Gorfinkiel
- School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
| | - Gustavo García
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas, Serrano 113-bis, 28006 Madrid, Spain
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Is there substituent cross-interaction effect in all the conjugated systems containing C N polar bond? The substituent effects on the NMR chemical shifts of 2,5-disubstituted pyrimidines. J Mol Struct 2018. [DOI: 10.1016/j.molstruc.2017.10.111] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Loupas A, Regeta K, Allan M, Gorfinkiel JD. Shape and Core-Excited Resonances in Thiophene. J Phys Chem A 2018; 122:1146-1155. [DOI: 10.1021/acs.jpca.7b11865] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alexandra Loupas
- Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus
de Caparica, Lisboa, 2829-516 Portugal
- School of Physical Sciences, The Open University,
Walton Hall, Milton Keynes MK7 6AA, United Kingdom
| | - Khrystyna Regeta
- Department of Chemistry, University of Fribourg, Fribourg 1700, Switzerland
| | - Michael Allan
- Department of Chemistry, University of Fribourg, Fribourg 1700, Switzerland
| | - Jimena D. Gorfinkiel
- School of Physical Sciences, The Open University,
Walton Hall, Milton Keynes MK7 6AA, United Kingdom
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9
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Brunger MJ. Electron scattering and transport in biofuels, biomolecules and biomass fragments. INT REV PHYS CHEM 2017. [DOI: 10.1080/0144235x.2017.1301030] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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10
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Regeta K, Allan M, Winstead C, McKoy V, Mašín Z, Gorfinkiel JD. Resonance effects in elastic cross sections for electron scattering on pyrimidine: Experiment and theory. J Chem Phys 2016; 144:024301. [PMID: 26772565 DOI: 10.1063/1.4937790] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We measured differential cross sections for elastic (rotationally integrated) electron scattering on pyrimidine, both as a function of angle up to 180(∘) at electron energies of 1, 5, 10, and 20 eV and as a function of electron energy in the range 0.1-14 eV. The experimental results are compared to the results of the fixed-nuclei Schwinger variational and R-matrix theoretical methods, which reproduce satisfactorily the magnitudes and shapes of the experimental cross sections. The emphasis of the present work is on recording detailed excitation functions revealing resonances in the excitation process. Resonant structures are observed at 0.2, 0.7, and 4.35 eV and calculations for different symmetries confirm their assignment as the X̃(2)A2, Ã(2)B1, and B̃(2)B1 shape resonances. As a consequence of superposition of coherent resonant amplitudes with background scattering the B̃(2)B1 shape resonance appears as a peak, a dip, or a step function in the cross sections recorded as a function of energy at different scattering angles and this effect is satisfactorily reproduced by theory. The dip and peak contributions at different scattering angles partially compensate, making the resonance nearly invisible in the integral cross section. Vibrationally integrated cross sections were also measured at 1, 5, 10 and 20 eV and the question of whether the fixed-nuclei cross sections should be compared to vibrationally elastic or vibrationally integrated cross section is discussed.
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Affiliation(s)
- Khrystyna Regeta
- Department of Chemistry, University of Fribourg, Chemin du Musée 9, CH-1700 Fribourg, Switzerland
| | - Michael Allan
- Department of Chemistry, University of Fribourg, Chemin du Musée 9, CH-1700 Fribourg, Switzerland
| | - Carl Winstead
- A. A. Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
| | - Vincent McKoy
- A. A. Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
| | - Zdeněk Mašín
- Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Strasse 2A, 12489 Berlin, Germany
| | - Jimena D Gorfinkiel
- Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
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