| 1. |
- Anderson, Emma K., et al.
(författare)
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Decays of excited silver-cluster anions Agn, n=4 to 7, in the Double ElectroStatic Ion Ring ExpEriment
- 2018
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 98:2
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Tidskriftsartikel (refereegranskat)abstract
- Spontaneous decays of small, hot silver-cluster anions Ag-n(-), n = 4-7, have been studied using one of the rings of the Double ElectroStatic Ion Ring ExpEriment (DESIREE). Observation of these decays over very long time scales is possible due to the very low residual gas pressure (similar to 10(-14)) and cryogenic (13 K) operation of DESIREE. The yield of neutral particles from stored beams of Ag-6(-) and Ag-2(-) anions were measured for 100 milliseconds and were found to follow single power-law behavior with millisecond time-scale exponential cutoffs. The Ag-4(-) and Ag-5(-) anions were stored for 60 s and the observed decays show two-component power-law behaviors. We present calculations of the rate constants for electron detachment from and fragmentation of Ag-4(-) and Ag-5(-). In these calculations, we assume that the internal energy distribution of the clusters are flat and with this we reproduce the early steep parts of the experimentally measured decay curves for Ag-4(-) and Ag-5(-) which extends to tens and hundreds of milliseconds, respectively. The fact that the calculations reproduce the early slopes of Ag-4(-) and Ag-5(-), which differ for the two cases, suggests that it is the changes in fragmentation rates with internal cluster energies of Ag-4(-) and Ag-5(-) rather than conditions in the ion source that determine this behavior. Comparisons with the measurements strongly suggest that the neutral particles detected in these time domains originate from Ag-4(-) -> Ag-3(-) + Ag and Ag-5(-) -> Ag-3(-) +Ag-2 fragmentation processes.
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| 2. |
- Anderson, Emma K., 1986-
(författare)
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DESIREE: Instrumentation Developments and Hot Metal Cluster Decays
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents instrumentation developments and measurements performed at the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. DESIREE operates at cryogenic temperatures ~13 K, with very low background pressures of ~10-14mbar, allowing the observation of stored ions to long times of tens of seconds and longer.Investigations into improving the count rate capability of the DESIREE detectors are presented. Microchannel plate (MCP) detectors are used for position sensitive particle counting in the DESIREE detector assemblies. In a cryogenic environment the operational resistance of MCPs is orders of magnitude higher than at room temperature and this limits the possible count rates. Novel low-resistance MCP detectors were investigated and resulted in the replacement of the MCPs in the DESIREE detector assemblies.DESIREE was used to measure spontaneous decays of hot, small cluster anions. The decays of small silver, copper and gold cluster anions are presented and compared to statistical model calculations. An experiment that is able to measure the proportion of spontaneous decay due to fragmentation or electron detachment in dimer anions of silver and copper is presented and significant, previously overlooked, contributions from electron detachment to the decay is identified. Furthermore, measurements of the stability and decay of small carbon cluster dianions are presented. These experiments utilised the aforementioned low-resistance MCPs.
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| 3. |
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| 4. |
- Anderson, Emma K., 1986-, et al.
(författare)
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Fragmentation of and electron detachment from hot copper and silver dimer anions : A comparison
- 2023
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 107:6
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Tidskriftsartikel (refereegranskat)abstract
- We measured the spontaneous decays of internally hot copper and silver dimer anions, and , stored in one of the two ion-beam storage rings of the Double Electrostatic Ion Ring Experiment (DESIREE) at Stockholm University. A coincidence detection technique was utilized enabling essentially background-free measurements of -> Cu + Cu- and -> Ag + Ag- fragmentation rates. Furthermore, the total rates of neutral decay products (monomers and dimers) were measured and the relative contributions of fragmentation and electron emission ( -> Cu2 + e- and -> Ag2 + e-) were deduced as functions of storage time. Fragmentation is completely dominant at early times. However, after about 20 ms of storage, electron emission is observed and becomes the leading decay path after 100 ms for both dimer anions. The branching ratios between fragmentation and electron emission (vibrationally assisted autodetachment processes) are very nearly the same for and Ag-2 throughout the present storage cycle of 10 seconds. This is surprising considering the difference between the electron affinities of the neutral dimers, Cu2 and Ag2, and the difference between the and the dissociation energies.
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| 5. |
- Anderson, Emma K., et al.
(författare)
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Spontaneous electron emission from hot silver dimer anions: Breakdown of the Born-Oppenheimer approximation
- 2020
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 124
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Tidskriftsartikel (refereegranskat)abstract
- We report the first experimental evidence of spontaneous electron emission from a homonuclear dimer anion through direct measurements of Ag−2 → Ag2 + e− decays on milliseconds and seconds timescales. This observation is very surprising as there is no avoided crossing between adiabatic energy curves to mediate such a process. The process is weak, yet dominates the decay signal after 100 ms when ensembles of internally hot Ag−2 ions are stored in the cryogenic ion-beam storage ring, DESIREE, for 10 s. The electron emission process is associated with an instantaneous, very large reduction of the vibrational energy of the dimer system. This represents a dramatic deviation from a Born-Oppenheimer description of dimer dynamics.
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| 6. |
- Aumayr, Friedrich, et al.
(författare)
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Roadmap on photonic, electronic and atomic collision physics : III. Heavy particles
- 2019
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 52:17
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Tidskriftsartikel (refereegranskat)abstract
- We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zero to relativistic speeds. Modern theoretical and experimental approaches provide detailed insight into the wide range of many-body interactions involving projectiles and targets of varying complexity ranging from simple atoms, through molecules and clusters, complex biomolecules and nanoparticles to surfaces and crystals. These developments have been driven by technological progress and future developments will expand the horizon of the systems that can be studied. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting nineteen contributions from leading scientists in the field.
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| 7. |
- Barklem, Paul, et al.
(författare)
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Mutual Neutralization in Li++H−/D− and Na++H−/D− Collisions : Implications of Experimental Results for Non-LTE Modeling of Stellar Spectra
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 908:2
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Tidskriftsartikel (refereegranskat)abstract
- Advances in merged-beams instruments have allowed experimental studies of the mutual neutralization (MN) processes in collisions of both Li+ and Na+ ions with D− at energies below 1 eV. These experimental results place constraints on theoretical predictions of MN processes of Li+ and Na+ with H−, important for non-LTE modeling of Li and Na spectra in late-type stars. We compare experimental results with calculations for methods typically used to calculate MN processes, namely the full quantum (FQ) approach, and asymptotic model approaches based on the linear combination of atomic orbitals (LCAO) and semiempirical (SE) methods for deriving couplings. It is found that FQ calculations compare best overall with the experiments, followed by the LCAO, and the SE approaches. The experimental results together with the theoretical calculations, allow us to investigate the effects on modeled spectra and derived abundances and their uncertainties arising from uncertainties in the MN rates. Numerical experiments in a large grid of 1D model atmospheres, and a smaller set of 3D models, indicate that neglect of MN can lead to abundance errors of up to 0.1 dex (26%) for Li at low metallicity, and 0.2 dex (58%) for Na at high metallicity, while the uncertainties in the relevant MN rates as constrained by experiments correspond to uncertainties in abundances of much less than 0.01 dex (2%). This agreement for simple atoms gives confidence in the FQ, LCAO, and SE model approaches to be able to predict MN with the accuracy required for non-LTE modeling in stellar atmospheres.
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| 8. |
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| 9. |
- Bernard, Jérôme, et al.
(författare)
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Efficient radiative cooling of tetracene cations C18H12+ : absolute recurrent fluorescence rates as a function of internal energy
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 25:15, s. 10726-10740
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Tidskriftsartikel (refereegranskat)abstract
- We have measured recurrent fluorescence (RF) cooling rates of internally hot tetracene cations, C18H12+, as functions of their storage times and internal energies in two different electrostatic ion-beam storage rings – the cryogenic ring DESIREE with a circumference of 8.6 meters in Stockholm and the much smaller room temperature ring Mini-Ring in Lyon, which has a circumference of 0.71 meters. The RF rates were measured to be as high as 150 to 1000 s−1 for internal energies in the 7 to 9.4 eV energy range, where we have probed the time evolution of the internal energy distribution with nanosecond laser pulses with a 1 kHz repetition rate. These RF rates are found to be significantly higher than those of previously investigated smaller PAHs such as e.g. anthracene and naphthalene, for which the lowest non-forbidden electronic excited state, the D2 state, is populated with a smaller probability by inverse internal conversion. Furthermore, the D2–D0 transition rate is smaller for these smaller molecules than for tetracene. The complementary features of the two storage rings allow for RF rate measurements in a broader internal energy range than has been possible before. The smaller sampling period of about 6 μs in Mini-Ring is ideal to study the cooling dynamics of the hotter ions that decay fast, whereas DESIREE with a sampling period of about 60 μs is better suited to study the colder ions that decay on longer timescales ranging up to hundreds of milliseconds. The excellent agreement between the two series of measurements in the region where they overlap demonstrates the complementarity of the two electrostatic ion-beam storage rings.
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| 10. |
- Bernigaud, Virgile, et al.
(författare)
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Electron capture-induced dissociation of AK dipeptide dications : Influence of ion velocity, crown-ether complexation and collision gas
- 2008
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Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 276:2-3, s. 77-81
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation of doubly protonated AK dipeptide ions has been investigated after collisional electron transfer. Electron capture leads to three dominant channels, H loss, NH3 loss, and N–Cα bond breakage to give either c+ or z+ fragment ions. The relative importance of these channels has been explored as a function of ion velocity, the degree of complexation with crown ether, and collision gas. Our results indicate that H loss and NH3 loss are competing channels whereas the probability of N–Cα bond breakage is more or less constant.
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