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DESIREE: Instrumentation Developments and Hot Metal Cluster Decays
Stockholm University, Faculty of Science, Department of Physics.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2019. , p. 84
Keywords [en]
DESIREE, microchannel plate, clusters, spontaneous decay, small metal cluster anions, silver, copper, gold, carbon dianions, fragmentation, vibrational autodetachment
Keywords [sv]
DESIREE, mikrokanalplattor, kluster, spontana sönderfall, små metallklusteranjoner, silver, koppar, guld, kol di-anjoner, fragmentering
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-167321ISBN: 978-91-7797-634-9 (print)ISBN: 978-91-7797-635-6 (electronic)OAI: oai:DiVA.org:su-167321DiVA, id: diva2:1298976
Public defence
2019-05-10, FP41, hus 1, AlbaNova universitetscentrum, Roslagstullbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2019-04-15 Created: 2019-03-25 Last updated: 2019-05-03Bibliographically approved
List of papers
1. Decays of excited silver-cluster anions Ag-n, n=4 to 7, in the Double ElectroStatic Ion Ring ExpEriment
Open this publication in new window or tab >>Decays of excited silver-cluster anions Ag-n, n=4 to 7, in the Double ElectroStatic Ion Ring ExpEriment
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2018 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 98, no 2, article id 022705Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-160075 (URN)10.1103/PhysRevA.98.022705 (DOI)000442804000005 ()
Available from: 2018-09-28 Created: 2018-09-28 Last updated: 2019-03-29Bibliographically approved
2. Spontaneous decay of small copper-cluster anions Cu-n(-) (n=3-6), on long time scales
Open this publication in new window or tab >>Spontaneous decay of small copper-cluster anions Cu-n(-) (n=3-6), on long time scales
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2017 (English)In: Physical Review A, ISSN 2469-9926, Vol. 95, no 2, article id 022511Article in journal (Refereed) Published
Abstract [en]

We have measured the spontaneous neutral particle emission from copper-cluster anions ( Cu-n(-), n = 3-6) stored at cryogenic temperatures in one of the electrostatic ion storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The measured rate of emission from the stored Cu-3(-) ions follows a single power-law decay for about 1 ms but then decreases much more rapidly with time. The latter behavior may be due to a decrease in the density of available final states in Cu-3 as the excitation energies of the decaying ions approach the electron detachment threshold. The emissions from Cu-4(-), Cu-5(-), and Cu-6(-) are well described by sums of two power laws that are quenched by radiative cooling of the stored ions with characteristic times between a few and hundreds of milliseconds. We relate these two-component behaviors to populations of stored ions with higher and lower angular momenta. In a separate experiment, we studied the laser-induced decay of Cu-6(-) ions that were excited by 1.13- or 1.45-eV photons after 46 ms of storage.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-142490 (URN)10.1103/PhysRevA.95.022511 (DOI)000395979500009 ()
Available from: 2017-05-15 Created: 2017-05-15 Last updated: 2019-03-29Bibliographically approved
3. Fragmentaion and detachemnt of hot silver and copper dimer anions
Open this publication in new window or tab >>Fragmentaion and detachemnt of hot silver and copper dimer anions
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(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-167320 (URN)
Available from: 2019-03-25 Created: 2019-03-25 Last updated: 2019-03-29Bibliographically approved
4. Dianion diagnostics in DESIREE: High-sensitivity detection of C-n(2-) from a sputter ion source
Open this publication in new window or tab >>Dianion diagnostics in DESIREE: High-sensitivity detection of C-n(2-) from a sputter ion source
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2018 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 89, no 3, article id 033112Article in journal (Refereed) Published
Abstract [en]

A sputter ion source with a solid graphite target has been used to produce dianions with a focus on carbon cluster dianions, C-n(2-), with n = 7-24. Singly and doubly charged anions from the source were accelerated together to kinetic energies of 10 keV per atomic unit of charge and injected into one of the cryogenic (13 K) ion-beam storage rings of the Double ElectroStatic Ion Ring Experiment facility at Stockholm University. Spontaneous decay of internally hot C-n(2-) dianions injected into the ring yielded C-n(2-) anions with kinetic energies of 20 keV, which were counted with a microchannel plate detector. Mass spectra produced by scanning the magnetic field of a 90 degrees analyzing magnet on the ion injection line reflect the production of internally hot C-7(2-) - C-24(2-) dianions with lifetimes in the range of tens of microseconds to milliseconds. In spite of the high sensitivity of this method, no conclusive evidence of C-6(2-) was found while there was a clear C-7(2-) signal with the expected isotopic distribution. This is consistent with earlier experimental studies and with theoretical predictions. An upper limit is deduced for a C-6(2-) signal that is two orders-of-magnitude smaller than that for C-7(2-). In addition, CnO2- and CnCu2- dianions were detected.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-155975 (URN)10.1063/1.5010077 (DOI)000428988300013 ()29604753 (PubMedID)
Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2019-03-29Bibliographically approved

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