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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 3P2 level is located and the lifetime of this sate is found to be longer than the storage time of the ion beam. We also find that a state exists higher in energy than the previously known level with a lifetime in the range of hundreds of milliseconds.

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.

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 through the rotational barrier. For storage times exceeding 100 ms, however, VAD is dominating. This process is driven by the very weak direct coupling between nuclear and electronic degrees of freedom.

The correlated Tunneling Transfer Ionization (TuTI) channel in fast 4-body processes p + He → H0 + He2+ + e is utilized to probe the highly correlated asymptotic parts of the He ground-state momentum space wave function. In this reaction, predominantly at large nuclear impact parameters, one electron in the He ground state is captured by the proton by tunneling through the two-center barrier when electron and proton velocity vectors resonantly match. The measured 3-particle final-state momentum distributions show characteristic features that we trace back to the highly correlated non-s2 components of the He ground-state momentum wave function. This conclusion is supported by a simple heuristic model.

We present the results of an experiment in which electrons have been scattered on CN- ions, over a collision energy range 0–60 eV. The experiment was performed at the heavy ion storage ring CRYRING. The CN- ions were stored in the ring and merged with a monoenergetic electron beam that was guided in to and out of the ring using strong magnetic fields. Both neutral and positive fragments from the collision process were detected with surface barrier detectors. It was found that pure detachment completely dominates over those channels which involves breaking the molecular bond. The threshold energy for the detachment process was found to be 7 eV. The cross section rose from zero to a maximum of about 5 · 10-16 cm2 just below 30 eV, after which it remained essentially constant. The threshold region was carefully investigated in an attempt to find resonance structure arising from the possible existence of the doubly charged ion, CN2-. The statistical uncertainty in the data was, however, too large to conclusively prove or disprove the existence of such a resonance.

Electrons have been scattered on in the energy range from 0 - 35 eV. A resonance structure in the detachment channel was observed at an energy of about 10 eV. To explain the structure, a potential curve was constructed from the isoelectronic ground-state potential curve and the repulsive Coulomb potential, and it is argued that the structure may be related to the population of a state. The state is predicted to decay primarily by electron emission since a large potential barrier prevents dissociation into .

We report on measurements of dissociative recombination of ions populated in a range of initial vibrational levels with free electrons in the energy range of 0 - 20 eV. A photodis-sociation technique was applied to modify the vibrational distribution, and the influence on the dissociative-recombination (DR) spectrum was studied. To estimate the vibrational distribution in the experiment, the results of a simple model calculation describing a part of the measured spectrum are presented. From the comparison between the experimental data and the model calculation, we conclude that when laser photodissociation is not applied, our result is consistent with a Franck - Condon vibrational distribution from the ion source. When laser photodissociation is applied, a dramatic change of the DR spectrum is observed, which is consistent with the expected effect, based on theoretical photodissociation cross sections.

We used the world's first hard x-ray FEL to investigate the response of molecular systems to the ultra-intense, femtosecond x-ray radiation. We report sequential multiphoton ionization, frustrated absorption and double core hole production mechanisms.

We use extremely intense, ultrashort soft X-Ray pulses generated by the LCLS X-Ray Free Electron Laser to investigate the production of molecular double core-hole states by sequential two-photon X-Ray absorption. The effect of critical LCLS parameters such as the number of photons per pulse, the pulse duration, and the focal spot size on the photoelectron and Auger spectra is modeled in detail and the results of these simulations are used as an aid in the interpretation of the experimental spectra obtained. The emphasis is on double core-hole formation in small polyatomic molecules such as CO2.

A merged-beams technique has been used to measure the rate coefficient ( nu sigma ) for radiative recombination (RR) as well as dielectronic recombination (DR) with C-like F3+ ions at relative energies up to 74 eV. The RR measurement is compared to a theory based on the hydrogenic approximation with an effective charge Zeff. The data indicate that Zeff is larger than the full ionic charge. This is believed to be due to incomplete screening. DR with Delta n=0 core excitations as well as DR with Delta n=1 core excitations is observed. Structures associated with all three terms of the ground-state configuration of F3+ are found in our spectra, whereas no sign is seen of the metastable 1s22s2p3 5S state.

The rate coefficient ( nu sigma ) for radiative recombination between free electrons and highly charged Si6+ and Si11+ ions has been measured in the energy region from 0 to 1 eV. The experimental results were obtained with a merged-beams technique. Knowledge about the relative velocity distribution allowed a direct comparison with theory. It was found that for Li-like Si11+, the effective charge to be used in a calculation developed for bare ions is the total ion charge, Zeff approximately=11. This is in agreement with earlier findings for H-like ions and other Li-like ions. For O-like Si6+, the effective charge is found to be Zeff approximately=9. For Si6+, the measured rate coefficient is more than a factor of two larger than calculations based on the total ion charge (Zeff=6). This shows evidence for significant incomplete screening in the case of Si6+.

Dielectronic recombination cross sections from the ground and metastable states of the Be-like ions C2+, O4+ and F5+, and the B-like ions O3+ and F4+, have been calculated and compared with experimental results obtained by a merged-beams technique. The comparison of theory and experiment is complicated by the presence of weak electric fields in the interaction region. However, the authors qualitatively explain the main features of their experimental results. In particular, for Be-like ions they find evidence of a large contribution from the initial 2s2p 3P metastable state recombining into an Auger metastable final state.

The high electrical resistance of a microchannel plate at cryogenic temperatures presents a severe limitation on the detection count rate at low temperatures. We are currently investigating the detector properties of a novel atomic layer deposition activated MCP developed by Gorelikov et al [1]. This is of particular interest to us as MCPs are used for particle detection at the cryogenic DESIREE facility at Stockholm University.

The study is focused on investigation of stereospecific interaction of amino acid enantiomers with chiral targets in collisions of 1 keV and ~ 1 eV energy using tandem mass spectrometry.

We have measured the rates of neutrals produced from 10 keV Cn− or CnH− (n=2, 4, 6, 8, and 10) ion beams stored in one of DESIREE's 14 K storage rings. For n=4, 6, and 8 we observe marked differences between Cn− and CnH− cooling rates as inverse internal conversion [cf. S. Martin et al (2013) Phys. Rev. Lett. 110, 063003] processes are effective for the Cn− ions only. Knowledge of the cooling rates of these ions are important for estimates of their formation and destruction rates in cold interstellar environments.

We have measured the spontaneous neutral particle emission from beams of copper cluster anions (Cu−N, N = 3 − 6) stored in an electrostatic storage ring. These experiments have show that multiple structural isomers may be present in the beam.

We investigate collisions of Polycyclic Aromatic Hydrocarbon cations with noble gases at center-of- mass energies close to 100 eV and below. Charged fragments are stored in a new version of the electrostatic ion beam trap ConeTrap. After storage for different well-defined times we extract the ions and use a reflectron based time-of-flight mass spectrometer to analyse the ion mass distributions. This will give information on secondary decay channels and the lifetime of the initially trapped fragment.

We have used one of the cryogenic ion storage rings of DESIREE to measure the lifetime of the 2P°1/2 level in the sulfur anion to be 503 ± 43 seconds. This is orders of magnitude longer than any previously measured lifetime in a negatively charged ion.

We have studied the fragmentation of Pyrene or hydrogenated Pyrene cations (C16H+10+x with x = 0, 5, 6 and 16) in collision with He. We find that the carbon backbone fragmentation cross section increases with the number of H atoms added. This suggests that hydrogenation does not protect PAHs in, e.g., harsh interstellar environments.

Experimental studies of the radiative lifetime of the sole excited state in the nickel anion are presented. Beams of Ni- stored in DESIREE at cryogenic temperatures were subject to photodetachment at different photon energies and the resulting neutrals collected. Preliminary analysis of the decay in neutral production yields a radiative lifetime of approximately 15 seconds for the 3d94s2 2D3/2 excited state.

We have measured the total cross sections and kinetic energy distributions of the neutral fragments for the mutual neutralization of C− and O− with C+, N+ and O+ by using a merged beam apparatus. A fine resolution in the kinetic energy spectra of the product neutral atoms has allowed us to uniquely identify the atomic states which are participating in the mutual neutralization process. A detailed analysis of the branching ratios sheds new light on these charge transfer processes.

In this work we study statistical fragmentation of Polycyclic Aromatic Hydrocarbon (PAH) molecules following collisions with keV ions. Dissociation and transition state energies for H- and H2-emissions from PAHs have been calculated and a simple electronic stopping model has been used to calculate collision-induced internal PAH temperatures. We find that H2 may be formed efficiently from pristine PAHs for internal ion temperatures above 2200 K.

We have performed an extensive set of experiments with focus on collisions between PAH or biomolecular cations and He atoms at center-of-mass energies around 100 eV. In this energy range, non-statistical fragmentation processes are important.

We have stored the first beams in one of the rings of the double electrostatic ion-storage ring, DESIREE at cryogenic and at room temperature conditions. At cryogenic operations the following parameters are found. Temperature; T= 13K, pressure; p 10(7) and storage lifetime of a C-2(-) beam; tau = 450 S.

We report on the ongoing commissioning of the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. Beams of atomic carbon anions (C‑) and smaller carbon anion molecules (C‑2, C‑3, C‑4 etc.) have been produced in a sputter ion source, accelerated to 10 keV or 20 keV, and stored successfully in the two electrostatic rings. The rings are enclosed in a common vacuum chamber cooled to below 13 Kelvin. The DESIREE facility allows for studies of internally relaxed single isolated atomic, molecular and cluster ions and for collision experiments between cat- and anions down to very low center-of-mass collision energies (meV scale). The total thermal load of the vacuum chamber at this temperature is measured to be 32 W. The decay rates of stored ion beams have two components: a non-exponential component caused by the space charge of the beam itself which dominates at early times and an exponential term from the neutralization of the beam in collisions with residual gas at later times. The residual gas limited storage lifetime of carbon anions in the symmetric ring is over seven minutes while the 1/e lifetime in the asymmetric ring is measured to be about 30 seconds. Although we aim to improve the storage in the second ring, the number of stored ions are now sufficient for many merged beams experiments with positive and negative ions requiring milliseconds to seconds ion storage.

We have investigated nonlinear processes in small molecules by x-ray photoelectron spectroscopy using the Linac Coherent Light Source free electron laser, and by simulations. The main focus of the experiments was the formation of the two-site double core-hole (tsDCH) states in the molecules CO2, N2O and N-2. These experiments are described in detail and the results are compared with simulations of the photoelectron spectra. The double core-hole states, and in particular the tsDCH states, have been predicted to be highly sensitive to the chemical environment. The theory behind this chemical sensitivity is validated by the experiments. Furthermore, our simulations of the relative integrated intensities of the peaks associated with the nonlinear processes show that this type of simulation, in combination with experimental data, provides a useful tool for estimating the duration of ultra-short x-ray pulses.

We have experimentally investigated electron transfer processes in collisions between 1.04 MeV protons stored in the electron-cooler ion-storage ring, CRYRING and molecular nitrogen in a supersonic gas jet. We report distributions of kinetic energies of molecular nitrogen ions in charge states 1-3 detected in coincidence with neutralized projectiles. Further, we investigate the influence of the relative orientation of the target molecular axis and the direction of the incoming projectile.

We have investigated collisions between Xe20+ ions and the isolated polycyclic aromatic hydrocarbon (PAH) C16H10 isomers pyrene and fluoranthene or pure clusters of either pyrene or fluoranthene. We show fragment distributions and intensities for both cases and rationalize the results by means of a classical over-the-barrier (COB) model in conjunction with quantum chemistry calculations of vertical ionization energies of pyrene and fluoranthene monomers. We find that comparatively small differences in the first and second ionization energies for these isomers have significant effects on both the monomer and cluster fragment distributions.

We report the result of a correction-free measurement of the lifetime of the metastable atomic negative helium ion. For all previous experimental investigations of the lifetime of the most long lived level of the He− ion, 1s2s2p 4P5/2, it was necessary to correct for systematic effects of the experimental environment as magnetically induced mixing with more short-lived fine structure components and/or photo detachment by the thermal radiation. In the present experiment any such influence on the measured lifetime has been effectively eliminated by performing the measurement in a cryogenic electrostatic ion-beam trap. With this technique we have reached a higher accuracy than earlier obtained. Our result with one standard deviation error is τ5/2 = (359.0±0.7)μs.

We describe the status of the DESIREE facility, which is an electrostatic ion-storage device consisting of two storage rings with a common section, where ion beams of opposite charges stored in the two rings are merged. The electrostatic storage rings are mounted in a single common vacuum vessel, which is isolated inside an outer vacuum chamber and cooled by means of four cryogenerators. This unique system will allow for studies of interaction among ions of opposite charges at well controlled conditions both in terms of internal degrees of freedom and relative velocity. An advanced ion-beam production system for intense pulses of cold complex molecular ions is also presented.