| 1. |
- Eklund, Gustav, et al.
(författare)
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Cryogenic merged-ion-beam experiments in DESIREE : Final-state-resolved mutual neutralization of Li+ and D-
- 2020
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 102:1
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Tidskriftsartikel (refereegranskat)abstract
- We have developed an experimental technique to study charge-and energy-flow processes in sub-eV collisions between oppositely charged, internally cold, ions of atoms, molecules, and clusters. Two ion beams are stored in separate rings of the cryogenic ion-beam storage facility DESIREE, and merged in a common straight section where a set of biased drift tubes is used to control the center-of-mass collision energy locally in fine steps. Here, we present measurements on mutual neutralization between Li+ and D- where a time-sensitive imaging-detector system is used to measure the three-dimensional distance between the neutral Li and D atoms as they reach the detector. This scheme allows for direct measurements of kinetic-energy releases, and here it reveals separate populations of the 3s state and the (3p + 3d) states in neutral Li while the D atom is left in its ground state 1s. The branching fraction of the 3s final state is measured to be 57.8 +/- 0.7% at a center-of-mass collision energy of 78 +/- 13 meV. The technique paves the way for studies of charge-, energy-, and mass-transfer reactions in single collisions involving molecular and cluster ions in well-defined quantum states.
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| 2. |
- Gatchell, Michael, 1988-, et al.
(författare)
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Stability of C59 Knockout Fragments from Femtoseconds to Infinity
- 2024
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 966:2
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the stability of C59 anions as a function of time, from their formation on femtosecond timescales to their stabilization on second timescales and beyond, using a combination of theory and experiments. The C-59 fragments were produced in collisions between C60 fullerene anions and neutral helium gas at a velocity of 90 km s−1 (corresponding to a collision energy of 166 eV in the center-of-mass frame). The fragments were then stored in a cryogenic ion beam storage ring at the DESIREE facility, where they were followed for up to 1 minute. Classical molecular dynamics simulations were used to determine the reaction cross section and the excitation energy distributions of the products formed in these collisions. We find that about 15% of the C-59 ions initially stored in the ring are intact after about 100 ms and that this population then remains intact indefinitely. This means that C60 fullerenes exposed to energetic atoms and ions, such as stellar winds and shock waves, will produce stable, highly reactive products, like C59, that are fed into interstellar chemical reaction networks.
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| 3. |
- Kristiansson, Moa K., 1989-, et al.
(författare)
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High-precision electron affinity of oxygen
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Negative ions are important in many areas of science and technology, e.g., in interstellar chemistry, for accelerator-based radionuclide dating, and in anti-matter research. They are unique quantum systems where electron-correlation effects govern their properties. Atomic anions are loosely bound systems, which with very few exceptions lack optically allowed transitions. This limits prospects for high-resolution spectroscopy, and related negative-ion detection methods. Here, we present a method to measure negative ion binding energies with an order of magnitude higher precision than what has been possible before. By laser-manipulation of quantum-state populations, we are able to strongly reduce the background from photodetachment of excited states using a cryogenic electrostatic ion-beam storage ring where keV ion beams can circulate for up to hours. The method is applicable to negative ions in general and here we report an electron affinity of 1.461 112 972(87) eV for O-16. High-precision measurements are useful to find isotopic shifts and electron correlation. Here the authors measure electron affinity and hyperfine splitting of atomic oxygen with higher precision than previous studies.
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| 4. |
- Najeeb, P. K., 1986-, et al.
(författare)
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Stability and Cooling of the C72- Dianion
- 2023
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 131:11
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the stability of the smallest long-lived all carbon molecular dianion (C72-) in new time domains and with a single ion at a time using a cryogenic electrostatic ion-beam storage ring. We observe spontaneous electron emission from internally excited dianions on millisecond timescales and monitor the survival of single colder C72- molecules on much longer timescales. We find that their intrinsic lifetime exceeds several minutes - 6 orders of magnitude longer than established from earlier experiments on C72-. This is consistent with our calculations of vertical electron detachment energies predicting one inherently stable isomer and one isomer which is stable or effectively stable behind a large Coulomb barrier for C72-→C7-+e- separation.
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| 5. |
- Najeeb, P. K., 1986-, et al.
(författare)
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Stability and Cooling of the C2−7 Dianion
- 2023
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 131:11
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the stability of the smallest long-lived all carbon molecular dianion () in new time domains and with a single ion at a time using a cryogenic electrostatic ion-beam storage ring. We observe spontaneous electron emission from internally excited dianions on millisecond timescales and monitor the survival of single colder molecules on much longer timescales. We find that their intrinsic lifetime exceeds several minutes—6 orders of magnitude longer than established from earlier experiments on . This is consistent with our calculations of vertical electron detachment energies predicting one inherently stable isomer and one isomer which is stable or effectively stable behind a large Coulomb barrier for →+e− separation.
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| 6. |
- Poline, Mathias, et al.
(författare)
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Mutual neutralisation of O+ with O− : investigation of the role of metastable ions in a combined experimental and theoretical study
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:43, s. 24607-24616
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Tidskriftsartikel (refereegranskat)abstract
- The mutual neutralisation of O+ with O− has been studied in a double ion-beam storage ring with combined merged-beams, imaging and timing techniques. Branching ratios were measured at the collision energies of 55, 75 and 170 (± 15) meV, and found to be in good agreement with previous single-pass merged-beams experimental results at 7 meV collision energy. Several previously unidentified spectral features were found to correspond to mutual neutralisation channels of the first metastable state of the cation (O+(2Do), τ ≈ 3.6 hours), while no contributions from the second metastable state (O+(2Po), τ ≈ 5 seconds) were observed. Theoretical calculations were performed using the multi-channel Landau–Zener model combined with the anion centered asymptotic method, and gave good agreement with several experimentally observed channels, but could not describe well observed contributions from the O+(2Do) metastable state as well as channels involving the O(3s 5So) state.
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| 7. |
- Poline, Mathias, et al.
(författare)
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Mutual Neutralization of NO plus with O-
- 2024
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 132:2
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Forskningsöversikt (refereegranskat)abstract
- We have studied the mutual neutralization reaction of vibronically cold NO+ with O- at a collision energy of approximate to 0.1 eV and under single-collision conditions. The reaction is completely dominated by production of three ground-state atomic fragments. We employ product-momentum analysis in the framework of a simple model, which assumes the anion acts only as an electron donor and the product neutral molecule acts as a free rotor, to conclude that the process occurs in a two-step mechanism via an intermediate Rydberg state of NO which subsequently fragments.
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| 8. |
- Poline, Mathias, et al.
(författare)
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Storage-ring study of the mutual neutralization of N plus with O minus
- 2022
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 105:6
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Tidskriftsartikel (refereegranskat)abstract
- The double ion storage ring DESIREE has been used in combination with position- and time-sensitive detectors to study the mutual neutralization of N+ with O- at 40 meV collision energy. Several previously unassigned spectral features observed in a recent single-pass merged-beams experiment at 7 meV collision energy [Phys. Rev. Lett. 121, 083401 (2018)], were also observed in the present experiment. It was found that neutralization channels of the first metastable state of the cation [N+(1D), τ≈ 256 s] could explain the majority of these features, while the second metastable state [N+(1S), τ≈ 0.9 s] was not found to contribute significantly. The branching ratios into the different electronically excited states of N were determined and found to be in good agreement between the two experiments. Theoretical calculations using the multichannel Landau-Zener model were found to yield good results for a number of channels, but could not describe some observed contributions, possibly due to the presence of other processes not accounted for in the model.
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| 9. |
- Poline, Mathias, et al.
(författare)
-
Storage-ring study of the mutual neutralization of N+ with O−
- 2022
-
Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 105:6
-
Tidskriftsartikel (refereegranskat)abstract
- The double ion storage ring DESIREE has been used in combination with position- and time-sensitive detectors to study the mutual neutralization of N+ with O− at 40 meV collision energy. Several previously unassigned spectral features observed in a recent single-pass merged-beams experiment at 7 meV collision energy [Phys. Rev. Lett. 121, 083401 (2018)], were also observed in the present experiment. It was found that neutralization channels of the first metastable state of the cation [N+(1D),τ≈256s] could explain the majority of these features, while the second metastable state [N+(1S),τ≈0.9s] was not found to contribute significantly. The branching ratios into the different electronically excited states of N were determined and found to be in good agreement between the two experiments. Theoretical calculations using the multichannel Landau-Zener model were found to yield good results for a number of channels, but could not describe some observed contributions, possibly due to the presence of other processes not accounted for in the model.
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| 10. |
- Schmidt-May, Alice F., 1988-, et al.
(författare)
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State-resolved mutual neutralization of 16O+ with 1H− and 2H− at collision energies below 100 meV
- 2024
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 109:5
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Tidskriftsartikel (refereegranskat)abstract
- We measured the product-state distribution and its dependence on the hydrogen isotope for the mutual neutralization between 16O+ and 1,2H− at the double electrostatic ion-beam storage ring DESIREE for center-of-mass collision energies below 100 meV. We find at least six product channels into ground-state hydrogen and oxygen in different excited states. The majority of oxygen products populate terms corresponding to 2?22?3(4?∘)4? with 5S∘ as the main reaction product. We also observe product channels into terms corresponding to 2?22?3(4?)3?. Collisions with the heavier hydrogen isotope yield a branching into these lower excited states smaller than collisions with 1H−. The observed reaction products agree with the theoretical predictions. The detailed branching fractions, however, differ between the theoretical results, and none of them fully agree with the experiment.
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