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Rotationally cold molecular ions in DESIREE: Threshold photodetachment thermometry of OH and OD
Stockholm University, Faculty of Science, Department of Physics.
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In experiments on molecular ions it is highly beneficial if the ions are in the electronic, vibrational and rotational ground state. Previous studies on these systems in ion traps or storage rings have been successful in preparing the molecular ions in the electronic and vibrational ground states, but the rotational degrees of freedom are experimentally more challenging due to their long relaxation times and the relatively small amounts of energy required for rotational excitations. Recent developments in electrostatic cryogenic storage devices have opened up possibilities of studying and controlling the rotational relaxation of molecular ions. This thesis presents experiments performed on the molecularions OH ̄ and OD ̄ stored in the cryogenic storage ring DESIREE at Stockholm University. The molecular ions are studied using a technique known as photodetachment thermometry, relying on detection of molecules neutralized through photodetachment as they are stored in the ring. By modeling the photodetachment cross section, we are able to measure the relative populations of rotational states and monitor the rotational relaxation of the molecular ions. The long storage times of DESIREE allow us to observe the rotational relaxation on timescales up to several relaxation lifetimes. From these measurements we are able to extract the intrinsic lifetime of the first excited rotational state of OH ̄ to be 183 ± 35 s. In addition to measuring the spontaneous rotational relaxation, we have also applied a selective photodetachment method to prepare an ensemble of ions at even lower internal temperature than what occurs spontaneously.

Place, publisher, year, edition, pages
Stockholm University, 2018.
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-162302OAI: oai:DiVA.org:su-162302DiVA, id: diva2:1265220
Presentation
2018-12-13, FA31, Roslagstullsbacken 21, Stockholm, 10:15 (English)
Opponent
Supervisors
Available from: 2019-06-11 Created: 2018-11-22 Last updated: 2019-06-11Bibliographically approved
List of papers
1. Rotationally Cold OH- Ions in the Cryogenic Electrostatic Ion-Beam Storage Ring DESIREE
Open this publication in new window or tab >>Rotationally Cold OH- Ions in the Cryogenic Electrostatic Ion-Beam Storage Ring DESIREE
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2017 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 7, article id 073001Article in journal (Refereed) Published
Abstract [en]

We apply near-threshold laser photodetachment to characterize the rotational quantum level distribution of OH- ions stored in the cryogenic ion-beam storage ring DESIREE at Stockholm University. We find that the stored ions relax to a rotational temperature of 13.4 +/- 0.2 K with 94.9 +/- 0.3% of the ions in the rotational ground state. This is consistent with the storage ring temperature of 13.5 +/- 0.5 K as measured with eight silicon diodes but in contrast to all earlier studies in cryogenic traps and rings where the rotational temperatures were always much higher than those of the storage devices at their lowest temperatures. Furthermore, we actively modify the rotational distribution through selective photodetachment to produce an OH- beam where 99.1 +/- 0.1% of approximately one million stored ions are in the J = 0 rotational ground state. We measure the intrinsic lifetime of the J = 1 rotational level to be 145 +/- 28 s.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-147089 (URN)10.1103/PhysRevLett.119.073001 (DOI)000407557300003 ()
Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2019-12-04Bibliographically approved

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