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| 2. |
- Sankari, Anna, et al.
(författare)
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Non-radiative decay and fragmentation in water molecules after 1a1-14a1 excitation and core ionization studied by electron-energy-resolved electron–ion coincidence spectroscopy
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:7
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we examine decay and fragmentation of core-excited and core-ionized water molecules combining quantum chemical calculations and electron-energy-resolved electron–ion coincidence spectroscopy. The experimental technique allows us to connect electronic decay from core-excited states, electronic transitions between ionic states, and dissociation of the molecular ion. To this end, we calculate the minimum energy dissociation path of the core-excited molecule and the potential energy surfaces of the molecular ion. Our measurements highlight the role of ultra-fast nuclear motion in the 1a1-14a1 core-excited molecule in the production of fragment ions. OH+ fragments dominate for spectator Auger decay. Complete atomization after sequential fragmentation is also evident through detection of slow H+ fragments. Additional measurements of the non-resonant Auger decay of the core-ionized molecule (1a1-1) to the lower-energy dication states show that the formation of the OH+ + H+ ion pair dominates, whereas sequential fragmentation OH+ + H+ → O + H+ + H+ is observed for transitions to higher dication states, supporting previous theoretical investigations.
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| 3. |
- Gisselbrecht, Mathieu, et al.
(författare)
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Charge migration and decay of doubly charged ammonia clusters
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:2, s. 022112-
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Tidskriftsartikel (refereegranskat)abstract
- The photo-fragmentation of ammonia molecular clusters ionized with soft x-rays is studied for photon energies near the N-1s threshold. The fragmentation is studied with a 3D momentum mass spectrometer to access the energy and angular correlations between fragments. By choosing the cluster sizes below or above the critical size of stable dication, we investigate the coulomb explosion dynamics and the interplay between charge delocalization and mobility of molecules in the clusters.
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| 4. |
- Kettunen, J. A., et al.
(författare)
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Valence electronic structure and photofragmentation of 1,1,1,2-tetrafluoroethane (CF3-CH2F)
- 2012
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 85:6
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and fragmentation of the hydrofluorocarbon compound 1,1,1,2-tetrafluoroethane (CF3-CH2F) were studied using spectroscopical methods and quantum chemical calculations. Valence photoelectron spectra and the ionic fragmentation products were recorded with synchrotron radiation in the vacuum ultraviolet (VUV) region. The geometric and electronic structures of the CF3-CH2F molecule were calculated using the complete active space perturbation theory of second order. The calculated vertical ionization energies were used to interpret the experimental photoelectron spectrum. VUV photodissociation of the sample molecule was studied with photoelectron-photoion coincidence spectroscopy. Coincident ion yields are shown for several cations as a function of electron binding energy. The experimental data are discussed in comparison with theory and previous work.
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| 5. |
- Kivimaki, A., et al.
(författare)
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Field ionization of high-Rydberg fragments produced after inner-shell photoexcitation and photoionization of the methane molecule
- 2015
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 143:11
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the production of neutral high-Rydberg (HR) fragments from the CH4 molecule at the C 1s -> 3p excitation and at the C 1s ionization threshold. Neutral fragments in HR states were ionized using a pulsed electric field and the resulting ions were mass-analyzed using an ion time-of-flight spectrometer. The atomic fragments C(HR) and H(HR) dominated the spectra, but molecular fragments CHx(HR), x = 1-3, and H-2(HR) were also observed. The production of HR fragments is attributed to dissociation of CH4+ and CH42+ ions in HR states. Just above the C 1s ionization threshold, such molecular ionic states are created when the C 1s photoelectron is recaptured after single or double Auger decay. Similar HR states may be reached directly following resonant Auger decay at the C 1s -> 3p resonance. The energies and geometries of the parent and fragment ions have been calculated in order to gain insight into relevant dissociation pathways. (C) 2015 AIP Publishing LLC.
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| 6. |
- Kivimaki, A., et al.
(författare)
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Synchrotron excitation - field ionization studies of high-Rydberg fragments produced after inner-shell ionization of small molecules
- 2015
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 635, s. 112121-112121
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Konferensbidrag (refereegranskat)abstract
- We have studied the production of neutral high-Rydberg (HR) fragments in small molecules after inner-shell excitation and ionization. Such fragments were ionized using a pulsed electric field and resulting ions were mass-analyzed with an ion time-of-flight (TOF) spectrometer. As an example, the results obtained at the C 1s ionization threshold of the methane molecule will be discussed.
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| 7. |
- Laksman, Joakim, et al.
(författare)
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Rapid bond rearrangement in core-excited molecular water.
- 2013
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:44, s. 19322-19329
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Tidskriftsartikel (refereegranskat)abstract
- The angular anisotropy of fragments created in the dissociation of core-electron excited water molecules is studied to probe the correlation between fragmentation channels, kinematics and molecular geometry. We present fragment kinetic measurements for water molecules where the inner-shell oxygen electron is excited to the unoccupied 4a1 and 2b2 valence molecular orbitals. The kinematics of individual fragmentation channels are measured using fully three-dimensional momentum imaging of fragments. The results show that the geometry of the molecule and the kinetic energy of fragments are strongly coupled in the atomisation process. In addition we identify a fragmentation process arising from bond rearrangement evidenced by the H2(+)-O(+) ion pair which is accessible for resonant excitation of the 1s electron. In all of the two-body fragmentation processes the dissociation takes place along the potential-energy surface, while atomisation reveals both dissociation along the potential surface and Coulomb explosion. The angular distribution of fragments suggests that the bond rearrangement is very rapid; likely on a sub 10 fs time scale.
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| 8. |
- Laksman, Joakim, et al.
(författare)
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Role of the Renner-Teller effect after core hole excitation in the dissociation dynamics of carbon dioxide dication.
- 2012
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:10
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation of the doubly-charged carbon dioxide molecule is studied after photoexcitation to the C 1s(1)2π(u) and O 1s(1)2π(u) states using a multicoincidence ion-imaging technique. The bent component of the Renner-Teller split states populated in the 1s→ π∗ resonant excitation at both the carbon and oxygen 1s ionization edges opens pathways to potential surfaces in highly bent geometries in the dication. Evidence for a complete deformation of the molecule is found in the coincident detection of C(+) and O(2) (+) ions. The distinct alignment of this fragmentation channel indicates rapid deformation and subsequent fragmentation. Investigation of the complete atomization dynamics in the dication leading to asymmetric charge separation shows that the primary dissociation mechanisms, sequential, concerted, and asynchronous concerted, are correlated to specific fragment kinetic energies. The study shows that the bond angle in fragmentation can extend below 20°.
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| 9. |
- Oghbaie, Shabnam, et al.
(författare)
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Dissociation of cyclopropane in double ionization continuum
- 2017
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Ingår i: Physical chemistry chemical physics : PCCP. - 1463-9084. ; 19:30, s. 19631-19639
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative double photoionization of cyclopropane is studied in the inner-valence region using tunable synchrotron radiation. With the aid of ab initio quantum chemical calculations the energies of dication states and their favoured fragmentation pathways are determined. These are compared to the experimental appearance energies of two-body fragmentation processes and to the kinetic energy released upon dissociation. Photon energy dependent state-selective dissociation in the 25–35 eV range is found. Calculations of dissociation pathways suggest that cyclopropane ring-deformation is selectively triggered at certain photon energies. The calculations suggest that initial ring deformation essentially determines the population of different dication states that function as gateways for particular dissociation channels. The measurements show that stepwise ionization processes populate dissociative 3e′−2 states via ring-opening and Jahn–Teller active states at photon energies below the double-ionization threshold. For energies above the double-ionization threshold the kinematics indicate that double ionization takes place predominantly within the Franck–Condon region populating 3e′−1 1e′′−1 states.
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| 10. |
- Oghbaie, Shabnam, et al.
(författare)
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Dissociation of cyclopropane in double ionization continuum
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:30, s. 19631-19639
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative double photoionization of cyclopropane is studied in the inner-valence region using tunable synchrotron radiation. With the aid of ab initio quantum chemical calculations the energies of dication states and their favoured fragmentation pathways are determined. These are compared to the experimental appearance energies of two-body fragmentation processes and to the kinetic energy released upon dissociation. Photon energy dependent state-selective dissociation in the 25-35 eV range is found. Calculations of dissociation pathways suggest that cyclopropane ring-deformation is selectively triggered at certain photon energies. The calculations suggest that initial ring deformation essentially determines the population of different dication states that function as gateways for particular dissociation channels. The measurements show that stepwise ionization processes populate dissociative 3e'(-2) states via ring-opening and Jahn-Teller active states at photon energies below the double-ionization threshold. For energies above the double-ionization threshold the kinematics indicate that double ionization takes place predominantly within the Franck-Condon region populating 3e'(-1) 1e ''(-1) states.
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