G. Eklund's research while affiliated with Stockholm University and other places

Publications (31)

Article
Full-text available
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 optical...
Article
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By repeatedly probing the a1Δ excited state and the X3Σ− ground-state populations in a beam of CH− ions stored in a cryogenic ion-beam storage ring for 100 s, we extract an intrinsic lifetime of 14.9±0.5 s for this excited state. This is far longer than all earlier experimental and theoretical results, exposing large difficulties in measuring and c...
Article
Full-text available
We present experimental final-state distributions for Mg atoms formed in Mg++D− mutual neutralization reactions at center-of-mass collision energies of 59±12 meV by using the merged-beams method. Comparisons with available full-quantum results reveal large discrepancies and a previously underestimated total rate coefficient by up to a factor of 2 i...
Article
Full-text available
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...
Article
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The properties of atomic negative ions are to a large extent determined by electron-electron correlation which makes them an ideal testing ground for atomic many-body physics. In this paper, we present a detailed experimental and theoretical study of excited states in the negative ion of iridium. The ions were stored at cryogenic temperatures using...
Article
Full-text available
The present paper reports on a merged-beam experiment on mutual neutralization between Na+ and D−. For this experiment, we have used the DESIREE ion-beams storage-ring facility. The reaction products are detected using a position- and time-sensitive detector, which ideally allows for determination of the population of each individual quantum state...
Preprint
Advances in merged-beams instruments have allowed experimental studies of the mutual neutralisation (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 modelling of...
Article
Full-text available
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...
Article
Full-text available
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...
Preprint
Full-text available
'Cookbook' style laboratory tasks have long been criticised for the lack of critical and independent thought that students need in order to complete them. We present an account of how we transformed a 'cookbook' lab to a genuine inquiry experiment in first year physics. Crucial features of the work were visits to see other teaching laboratories, un...
Article
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We report the first experimental evidence of spontaneous electron emission from a homonuclear dimer anion through direct measurements of Ag2−→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 do...
Article
Full-text available
Synopsis The electronic structure and the fragmentation dynamics of a series of isolated cyclic-dipeptides (cyclo-Ala-Ala; cyclo-Gly-Ala; cyclo-Gly-Gly) have been studied by mass spectrometry, photoemission and photoelectron-photoion coincidence spectroscopy.
Article
Full-text available
An overview of recent experimental results of studies of negative atomic and molecular ions in the Double ElectroStatic Ion-Ring ExpEriment, DESIREE is given. Metastable level lifetimes in atomic negative ions have been measured by time-dependent laser photodetachment. Rotational relaxation of diatomic anions is studied by near-threshold photodetac...
Article
Full-text available
Synopsis The decay of hot copper dimer anions is studied in a cryogenic storage ring. We detect atomic anion and neutral products and determine the fragmentation and vibrational autodetachment (VAD) rates separately. For short storage times the dimer anions predominantly decay by fragmentation of highly rotationally excited ions by tunneling throug...
Article
Full-text available
Synopsis Anions of iridium were stored in the cryogenic storage ring, DESIREE [1, 2, 3] and investigated using laser photodetachment. The ions were stored for up to 2000 seconds and the relaxation of several metastable states were studied by selecting different photon energies. The threshold of the previously not observed ³ P 2 level is located and...
Article
Full-text available
Synopsis We have performed a merged beam experiment on mutual neutralization of Li ⁺ and D ⁻ , at center of mass energies close to 0 eV using the DESIREE storage rings. The final state channels Li(3s) and Li(3p+3d) are resolved and the branching ratio is found to be more equal than predicted from theoretical models.
Article
Full-text available
Synopsis We have studied the stabilities of small carbon dianion clusters, C n 2 − (n = 7 – 11) in the cryogenic electrostatic ion storage ring, DESIREE. We observe spontaneous electron emission for tens of milliseconds, where dianions containing an even number of carbons decay slower in comparison to their neighbouring cluster sizes. For all the s...
Preprint
We report the first experimental evidence of spontaneous electron emission from a homonuclear dimer anion through direct measurements of $\rm{Ag}_2^- \rightarrow \rm{Ag}_2 + \rm{e}^-$ decays on milliseconds and seconds time scales. This observation is very surprising as there is no avoided crossing between adiabatic energy curves to mediate such a...
Article
Ultraslow radiative cooling lifetimes and adiabatic detachment energies for three astrochemically relevant anions, Cn− (n = 3–5), are measured using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) infrastructure at Stockholm University. DESIREE maintains a background pressure of ≈10⁻¹⁴ mbar and temperature of ≈13 K, allowing storage of mass-...
Preprint
Ultraslow radiative cooling lifetimes and adiabatic detachment energies for three astrochemically relevant anions, C$_n^-$ ($n=3-5$), are measured using the Double ElectroStatic Ion Ring ExpEriment (DESIREE) infrastructure at Stockholm University. DESIREE maintains a background pressure of $\approx$10$^{-14}$\,mbar and temperature of $\approx$13\,K...
Article
Spontaneous decays of small, hot silver-cluster anions Agn−, n=4–7, have been studied using one of the rings of the Double ElectroStatic Ion Ring ExpEriment (DESIREE). Observation of these decays over very long time scales is possible due to the very low residual gas pressure (∼10−14) and cryogenic (13 K) operation of DESIREE. The yield of neutral...
Preprint
Full-text available
Spontaneous decays of small, hot silver cluster anions Ag$_{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 ($\sim10^{-14}$) and cryogenic (13 K) operation of DESIREE. The yiel...
Preprint
A sputter ion source with a solid graphite target has been used to produce dianions with a focus on carbon cluster dianions, $\text{C}_{n}^{2-}$, 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 sto...
Article
A sputter ion source with a solid graphite target has been used to produce dianions with a focus on carbon cluster dianions, Cn2−, 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 t...
Conference Paper
Full-text available
We store a 10 keV OH⁻ ion-beam at 13.5 ± 0.5 K in one of the DESIREE storage rings. Using photodetachment thermometry we measure the effective relative photodetachment cross section at different storage times and determine the rotational temperature of the ions to be 13.4 ± 0.2 K in agreement with the macroscopic temperature. A model cross section...
Article
Full-text available
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...
Article
Full-text available
Measurements of the radiative lifetimes of the two excited states of the platinum anion Pt⁻ are presented. Pt⁻ ions stored in the cryogenic ion storage ring DESIREE were photodetached at different photon wavelengths and the resulting yield of neutral Pt measured as a function of time was recorded. Analysis of the neutral decay curves show a 2.54 ±...
Article
Full-text available
We have measured the spontaneous neutral particle emission from copper-cluster anions (Cun−, 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 Cu3− ions follows a single power-law decay...
Article
The intrinsic radiative lifetimes of the 5d106sS1/22 and 5d96s2 D3/22 bound excited states in the platinum anion Pt− have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5d106s S1/22 state was measured to be 2.54±0.10s, whil...

Citations

... This method would be particularly powerful for long-lived metastable states along with complementary studies such as the recent lifetime measurement of metastable CH − (>10 s) at DESIREE. 52) At RICE, we are currently working towards the photodetachment spectroscopy of C À 2 using a laser ablation source to see the difference between the initial temperatures. Experiments with extended storage times to more than several seconds are also in preparation. ...
... Here, E c.m. is the center-of-mass kinetic energy before the interaction, and E K is the kinetic energy released in the specific reaction channel. This particular three-dimensional imaging technique of two particles was first introduced by Amitay and Zajfman [21] for the study of the dissociative recombination reaction [22][23][24] but has since been employed for a number of MN systems, such as Li + /D − [19,25], Mg + /D − [26], and O + /O − [27,28]. The resulting spectrum represents a distribution of the final-state center-of-mass kinetic energy over the longitudinal extension of the interaction region and the collision-energy spread. ...
... Here, E c.m. is the center-of-mass kinetic energy before the interaction, and E K is the kinetic energy released in the specific reaction channel. This particular three-dimensional imaging technique of two particles was first introduced by Amitay and Zajfman [21] for the study of the dissociative recombination reaction [22][23][24] but has since been employed for a number of MN systems, such as Li + /D − [19,25], Mg + /D − [26], and O + /O − [27,28]. The resulting spectrum represents a distribution of the final-state center-of-mass kinetic energy over the longitudinal extension of the interaction region and the collision-energy spread. ...
... This allows the ions to decay to the vibrational ground state and relax their rotational excitations [14]. The lifetime is measured by repeatedly probing the stored ion beam through photodetachment by laser pulses [15][16][17]. DESIREE consists of two electrostatic ion-beam storage rings with a common straight section for merged-beams studies of sub-eV ion-ion collisions [12,13]. The storage rings are enclosed in a single vacuum chamber and cryogenically cooled to a temperature of 13.5 ± 0.5 K. Beams of CH − are produced in a cesium-sputter ion source, using ethanol vapor. ...
... The resulting spectrum represents a distribution of the final-state center-of-mass kinetic energy over the longitudinal extension of the interaction region and the collision-energy spread. By simulating these distributions using the Monte Carlo method and fitting them to the data, the branching ratios can be extracted [19,29]. They are corrected for the energy-dependent efficiency related to the angular acceptance of the detectors (for more details see Ref. [28]). ...
... For the MN of Mg þ with H − , the electronic structure of the Mg þ ground state [Ne]3s 2 S with its unpaired valence electron leads to a large number of available channels. Thus the complexity of the theoretical descriptions increases significantly in comparison with cases where the positive ion has a closed outer shell, such as for, e.g., Li þ or Na þ colliding with H − [13][14][15]45]. For closed-shell systems, rate coefficients determined with the FQ method have so far been extensively used for collisional-radiative modeling of astrophysical spectra. ...
... The experiments were carried out at the double electrostatic ion-beam storage-ring facility Double ElectroStatic Ion Ring ExpEriment (DESIREE) (Stockholm University, Sweden), an ultrahigh-vacuum device operated at cryogenic temperatures of about 13 K. This experimental setup was described previously by Thomas et al. [17] (design and technical description), Schmidt et al. [18] (first commissioning), and Eklund et al. [19] (first mutual neutralization experiment) and is only briefly discussed here. ...
... Photodetachment from very highly excited rotational states of the X 3 − state is energetically possible as well (see Fig. 1). High rotational states are known to be populated in sputter ion sources, which has been seen in experiments on long timescales by infrared inactive metal dimer anions [20,21]. However, photodetachment from such states is unlikely in the present experiment on CH − as energy conservation would require large changes of rotational quantum numbers. ...
... The development of cryogenic storage rings has opened the possibility to study cooling processes on very long time scales in the laboratory. [3][4][5][6][7][8] The extension of feasible storage times to thousands of seconds in these devices places a special emphasis on the understanding of this long time emission of thermal infrared photons from stored ions 4, [6][7][8][9][10][11][12] Before embarking on such a calculation of rate constants and energy distributions, it is worthwhile to consider two aspects of the thermal description of the vibrational degrees of freedom of a molecule or cluster. One is the question of ergodicity. ...
... The lines in Fig. 4 show fits to this functional form. Powerlaw decay curves over time are commonly observed from the spontaneous decay of ensembles of hot molecular ions or clusters with broad internal energy distributions and have been reported for a wide range of systems 39,[42][43][44][45][46][47][48] . This typically occurs when a diverse ensemble of decaying units with many different time constants coexist. ...