Electrostatic Storage Ring Research Articles

An electrostatic storage ring with a merging electron beam device at KEK

Biomolecular ions have been stored in an electrostatic storage ring at KEK. The lifetimes and intensities of these ions are suitable for research on atomic collisions. In order to study electron-biomolecular ion collisions, an electron target was constructed and installed in one of the straight sections of the ring. The structure of the device is the same as that of an electron cooler with an adiabatically expanded electron beam. The design of the electron target and the experimental results are presented.

Dynamics of neutral molecules stored in a ring

A decelerated beam of neutral ammonia molecules is injected into an electrostatic storage ring. Electrostatic lenses are used to map the emittance of the decelerator onto the acceptance of the ring. The tangential velocity spread of the package of molecules in the ring is set to less than $1\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$. The package of molecules can be observed for more than 50 distinct round trips, corresponding to $40\phantom{\rule{0.3em}{0ex}}\mathrm{m}$ in circular orbit and almost $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ storage time, sufficiently long for a first investigation of its transversal motion in the ring.

MONO1001: A source for singly charged ions applied to the production of multicharged fullerene beams

The present article reports on a recent study of the production of multiply charged fullerene beams based on an electron cyclotron resonance (ECR) ion source (ECRIS). As collision studies in fundamental physics are demanding intense beams of multiply charged ions of small molecules, clusters, and particularly of fullerenes, we have further developed the ion source ECRIS MONO1000 [P. Jardin et al., Rev. Sci. Instrum. 73, 789 (2002)], originally devoted to produce singly charged ions, towards the production of multiply charged fullerene beams. In this article, the test measurements performed at the Electrostatic Ion Storage Ring Århus rf power (ELISA) facility will be described. Typical mass spectra (from pure C60 and C70 powder) will be shown and the influence of several source parameters (rf power, support gas, gas pressure,…) will be discussed specifying the conditions necessary for an optimum ion source operation.

FIRE—the Frankfurt Ion stoRage Experiments

Existing electrostatic storage rings have proven to be a valuable tool for molecular and atomic physics in the low-energy regime. At the new Stern-Gerlach Center of Frankfurt University a small machine for ion energies up to 50 keV will be build up. It will serve as a tool to analyze the structure and dynamics of many particle systems from atoms to complex organic biomolecules. It will be possible to prepare the particle beams of interest in novel and unique ways. In direct comparison to traditional setups, the luminosity of the measurements will be improved by many orders of magnitude. In combination with the newest reaction microscopes, the F rankfurt I on sto R age E xperiments (FIRE) will allow analysis of many particle fragmentation processes of atoms and molecules with unrivaled resolution and completeness. In contrast to experiments with traps, an electrostatic storage ring has the advantage of being able to record the momenta of all neutral fragments. This paper gives an overview of the design parameters, the optical elements used and the project status.

Electron–Biomolecular Ion Collisions in an Electrostatic Storage Ring

Electron–biomolecular ion collisions were studied using an electrostatic storage ring with a merging beam technique for singly protonated peptides and multiply deprotonated DNA ions. The neutral-particle production rates according to collisions were measured. For peptides, resonant neutral-particle emissions were observed at a relative energy of 6.5 eV with a shoulder at around 9 eV. These resonances are deduced to come from electron capture and a subsequent cleavage of peptide bonds. For DNAs, neutral-particle emissions start from definite threshold energies, which depend on the ion charges. The neutrals come from a break of DNAs, rather than electron detachment.

Experimental studies of the photophysics of gas-phase fluorescent protein chromophores

To better understand the photophysics of photoactive proteins, the absorption bands of several gas-phase biomolecules have been studied recently at the electrostatic heavy-ion storage ring ELISA by a photo-fragmentation technique. In the present paper we discuss the involved photophysics and photochemistry for protonated and deprotonated model chromophores of the Green Fluorescent Protein (GFP) and the Red Fluorescent Protein (RFP). We show specifically that the delayed dissociation after photoabsorption can be understood in terms of a thermally activated process of the Arrhenius type. The rate of dissociation as a function of time after laser excitation is modeled in a calculation which is based on calculated heat capacities of the chromophores. Absorption of only one photon is enough to dissociate the deprotonated GFP chromophore on a time scale of milliseconds whereas absorption of two to three photons occurs for other chromophore ions. The difference is attributed to different activation energies, pre-exponential factors and locations of the absorption bands. We obtain activation energies for the dissociation that are of the order of 1–3 eV. Collision-induced dissociation experiments were performed to help identifying the fragmentation channels. Loss of methyl is found to be the dominant fragmentation channel for the deprotonated GFP chromophore and is also likely to be important for the protonated GFP chromophore at high temperatures. Other channels are open for the RFP chromophores. For the deprotonated RFP chromophore there is evidence that dissociation occurs through a non-trivial dissociation with substantial rearrangement.

Photodissociation of protonated amino acids and peptides in an ion storage ring. Determination of Arrhenius parameters in the high-temperature limit

We have measured the time dependence of the fragmentation of protonated amino acids and peptides upon UV excitation in an electrostatic ion storage ring. After absorption of a 266 nm photon, protonated Trp (TrpH+) has a lifetime of 10–20 μs but also a component with a millisecond lifetime is present. The long lifetime may be due to fluorescence, which leads to ions with lower excitation energy, or to the decay of the Trp+˙ radical cation formed after prompt hydrogen loss in the laser interaction region. Only one component with a lifetime of about 10 μs was detected for TyrH+. The lifetime of photoexcited PheH+ is even shorter with an upper limit of a few microseconds. For the singly protonated tripeptides (LysTrpLysH+ and LysTyrLysH+), the decay curves are found to consist of a single component that can be reproduced with an assumption of statistical decay after equilibration of the photon energy among all vibrational modes. The rate constant is expressed in the Arrhenius form in terms of the microcanonical temperature, and the decay rate is obtained by integration over the energy distribution, which has a spread corresponding to the canonical energy distribution at room temperature. The resulting deviation from exponential decay makes it possible to determine the decay parameters from a measurement at a single photon wavelength. Activation energies of Ea = 1.24 ± 0.07 and 1.5 ± 0.4 eV were determined for LysTrpLysH+ and LysTyrLysH+, respectively, with pre-exponential factors of Ad = 1011.1±0.5 and 1012.9±2.6 s−1.

Gas-Phase Studies of Chromophore Molecules in an Electrostatic Storage Ring

The use of an electrostatic storage ring for the study of chromophore ions in the gas phase is demonstrated. In this way the intrinsic photophysics and photochemistry of “naked” chromophore ions without the “disturbance” of a solvation shell is elucidated. The ring is combined with an electrospray ion source which enables the production of large molecular ions. Experiments described here involve absorption spectroscopy of protein chromophores and measurements of lifetimes for dissociation processes and excited states of nucleotide and protoporphyrin ions. Comparisons with solution phase experiments allow us to address the perturbation of a solvent or a protein environment on the electronic structure of chromophores.

Gas-phase absorption properties of a green fluorescent protein-mutant chromophore: The W7 clone

The gas-phase absorption properties of a blue GFP-mutant chromophore have been investigated in an electrostatic heavy-ion storage ring combined with an electrospray ion source. From the production of neutral photofragments, the gas-phase absorption profiles of both protonated and deprotonated forms have been obtained and compared with their homologues in the liquid phase and in the protein. Maximum absorption for the anion is found around 456 nm in solution and in the gas phase. It matches one absorption maximum in the W7 protein, which suggests that this is due to an anionic form of the chromophore—similar to the case of the GFP. For the W7 chromophore cation, the gas-phase absorption band exhibits a doublet feature in the gas-phase with maxima at 454 and 477 nm. Solvation effects are more pronounced for the cation than for the anion and the observed shifts in the absorption maxima may be explained by charge delocalization.

Resonant neutral-particle emission in collisions of electrons with peptide ions in a storage ring.

Electron-biomolecular ion collisions were studied using an electrostatic storage ring with a merging beam technique for singly protonated peptides (angiotensin I, II, and III). A strong neutral-particle emission at around 6.5 eV was found in addition to neutrals from recombination at low energies. The rates of the high-energy peak greatly decreased with a slight decrease in the number of amino-acid residues from angiotensin I to III. These results suggest that some peptide bonds were selectively cleaved.

Vibrationally resolved photoabsorption spectroscopy of red fluorescent protein chromophore anions.

Photoabsorption studies of red fluorescent protein chromophore anions have been performed at the ELISA electrostatic heavy-ion storage ring. The broad absorption band due to electronic excitation of the chromophores is tuned to a longer wavelength (redshifted) by extending the electronic conjugation of the molecule. A clear vibrational progression is resolved with E(vib) approximately 380 and 520 cm(-1) for two different forms of the chromophore. The vibrational modes correspond to collective motions of the entire molecular structure. It is argued that the excited electronic state has an equilibrium configuration far from that of the electronic ground state, i.e., poor Franck Condon overlap.

Possibilities of Electron Cooling in Low Energy Electrostatic Storage Rings

The application of an electrostatic ring for storage of ions with energies of several tens of keV is attractive for atomic and molecular science. The main goal of the KEK electrostatic ring is the storage of bio-molecular ions with atomic numbers of A ≈ 1000–10,000. An electron-beam cooler/target was installed in the KEK electrostatic ring for electron cooling and studying of electron-ion collisions. In accordance with simulations application of an electron cooler permits one to suppress multiple scattering of the stored ions with the residual gas atoms and thereby to increase the ion lifetime several times.

Design Studies of an Electrostatic Storage Ring

The design of a small electrostatic storage ring for all different kinds of ions at energies up to 50 keV is presented in this paper. One quarter of such a ring is presently being build up at IAP to study injection, optimize the optical elements and integrate the diagnostic system.

Storage of bio-molecular ions in the electrostatic storage ring

Abstract Singly or multiply charged bio-molecular ions produced with an electrospray ion source are stored in an electrostatic storage ring after being bunched and mass-analyzed. The measured 1/e-lifetimes of stored ions are from 12–20 s. These lifetimes are long enough to cool vibrationally excited molecular ions, and their intensities are tolerable for practical use, like atomic-collision experiments.

Lifetime measurement of the metastable Be- ion usingan electrostatic ion storage ring

The lifetime of the metastable Be-(2s2p2 4P3/2)ion has been measured to be 43.40±0.10 µs by means ofan electrostatic heavy-ion storage ring. This value is ingood agreement with the previously reported lifetime obtainedusing a magnetic storage ring, but more than 3% longer than thelifetime recently measured utilizing a newly constructedelectrostatic ion trap.

An electrostatic storage ring for atomic and molecular science

An electrostatic storage ring with a circumference of 8.1 m was designed for the research of atomic and molecular science. The race-track ring consists of two 160° deflectors, four 10° deflectors and four quadrupole doublets. For the 160° deflectors, a cylindrical shape has been adopted. In this ring, there are four types of stable regions with and without waists of the beam envelope in the middle of the deflectors. A beam test was performed with 20-keV ion beams from an ECR ion source. The observed lifetimes of beams stored in each stable region were different under the same conditions, except for the tune values. The lifetimes did not depend much on the injected beam intensity for a current of less than about 100 nA. The design and performance of the electrostatic storage ring are presented.

The combination of an electrospray ion source and an electrostatic storage ring for lifetime and spectroscopy experiments on biomolecules

An electrospray ion source has been coupled to an accelerator that injects ions into an electrostatic heavy-ion storage ring. Since the dc ion current produced by electrospray ionization is low (∼106 ions/s), ions are accumulated in a cylindrical ion trap filled with a helium buffer gas. The ions are collisionally damped in the buffer gas and confined to the central trap region by a rf field. Extraction from the trap occurs within a few microseconds and after acceleration through 22 kV, the ions of interest are selected by a magnet according to their mass to charge ratio. The ion bunch is subsequently injected into the ring. Both positive and negative ions have been stored, with masses ranging over 3 orders of magnitude (∼102–104 Da). From a pickup signal in the ring, the number of ions in a bunch is estimated to be of the order of 103–104 when the accumulation time is 0.1 s. Our first measurements show that we can store a sufficient number of ions to study the decay of metastable ions and to determine relative destruction cross sections. The technique could be useful to probe conformers differing only in size. Furthermore, our setup can be used for spectroscopic measurements of the ion-photon interaction such as the excitation of [Cytochrome c+17H]17+ protein ions with 532 nm photons.

Absorption spectrum of the green fluorescent protein chromophore anion in vacuo.

A sensitive photoabsorption technique for studies of gas-phase biomolecules has been used at the ELISA electrostatic heavy-ion storage ring. We show that the anion form of the chromophore of the green fluorescent protein in vacuo has an absorption maximum at 479 nm, which coincides with one of the two absorption peaks of the protein. Its absorption characteristics are therefore ascribed to intrinsic chemical properties of the chromophore. Evidently, the special beta-can structure of the protein provides shielding of the chromophore from the surroundings without significantly changing the electronic structure of the chromophore through interactions with amino acid side chains.

Radiative cooling of fullerene anions in a storage ring

Thermionic emission from hot fullerene anions, CN , has been measured in an electrostatic storage ring for evenN values from 36 to 96. The decay is quenched by radiative cooling and hence the observations give information on the intensity of thermal radiation from fullerenes. The experiments are analysed by comparison with a simulation which includes the quantisation of photon energy and the statistics of emission. Experiments with heating of the molecules with a laser beam conrm the interpretation of the observations in terms of radiative cooling and give an independent estimate of the cooling rate for C60. The measured cooling rates agree in general within a factor of two with the prediction from a classical dielectric model of a thermal radiation intensity of 300 eV/s for C60 at 1 400 K, scaling approximately with the 6th power of the temperature and with the number of atoms in the molecule. PACS. 36.40.-c Atomic and molecular clusters { 36.40.Cg Electronic and magnetic properties of clusters { 36.40.Qv Stability and fragmentation of clusters { 36.40.Wa Charged clusters { 39.10.+j Atomic and molecular beam sources and techniques

Observation of a 1/t decay law for hot clusters and molecules in a storage ring.

The exponential law is valid both for decay from a single quantum state into a continuum and for an ensemble maintained in thermal equilibrium. For statistical decay of an ensemble of isolated systems with a broad energy distribution, the exponential decay is replaced by a 1/t distribution. We present confirmation of this decay law by experiments with cluster anions in a small electrostatic storage ring. Deviations from the 1/t law for such an ensemble give important information on the dynamics of the systems. As examples, we present measurements revealing strong radiative cooling of anions of both metal clusters and fullerenes.