Small tungsten cluster anions Wn− (n=4–9 and 18–20) are stored in a Penning trap and electronically excited by photoabsorption (Ehν=1.815, 2.33, 3.5, and 4.66 eV). Delayed electron emission is observed on the milliseconds time scale by systematic variation of the storage duration between laser excitation and ion detection. Even if the photon energy exceeds the electron detachment energy, electrons are emitted several milliseconds after laser excitation. The electron emission time constant is determined as a function of the laser pulse energy. An Arrhenius analysis suggests that the observed delayed electron emission is a thermal process in analogy to thermionic emission of bulk materials. As shown by these experiments there is a simple rule for the dominating cooling channel of laser excited clusters: thermionic emission generally occurs as long as the electron binding energy is lower than the dissociation energy.

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Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser systems specialized on the specific needs of laser spectroscopy at storage rings is reported.

Recently, intense beams of highly charged ions have become available at heavy ion cooler rings. The obstacle for producing these highly interesting candidates is the large binding energy of K-shell electrons in heavy systems in excess of 100 keV. One way to remove these electrons is to strip them off by passing the ion through material. In the cooler ring, the ions are cooled to a well defined velocity. At the SIS/ESR complex it is possible to produce, store, and cool highly charged ions up to bare uranium with intensities exceeding 108 atoms in the ring. This opens the door for precision laser spectroscopy of hydrogenlike-heavy ions, e.g.209Bi82+, and allows to examine the interaction of the single electron with the large fields of the heavy nucleus, exceeding any artificially produced electric and magnetic fields by orders of magnitude. In the electron cooler the interaction of electrons and highly charged ions otherwise only present in the hottest plasmas can be studied.

Photo fragmentation studies of stored mass selected metal cluster ions of a large size range are reported. The experimental method and the data evaluation are described in detail. Gold cluster ions were produced by laser vaporization and stored in a Penning trap. After size selection they were electronically excited by irradiation with a pulsed laser beam. Relaxation by evaporation of neutral atoms and dimers was observed as a function of photon energy. From these data upper and lower limits for dissociation energies are determined for Au-n(+) (n = 3 to 23).

An electron beam ion trap is used to produce and confine highly-charged atomic ions in an energetic electron beam (electron trapping mode). After switching off the electron beam the ions remain trapped due to the external magnetic and electric fields. We have investigated the properties of this magnetic trapping mode by use of Fourier transform ion cyclotron resonance mass spectrometry. We found that the number of highly charged ions and the relative species abundance is nearly the same just before and just after turning off the electron beam. The electron trapping mode thus represents an ideal method for filling the trap in situ without the losses associated with transferring the ions from external sources. About 105 ions per highly charged species, such as 84Kr35+, were shown to exist in the trap in the magnetic trapping mode. A lower limit of 1.5 s was placed on the ion confinement time. This length is sufficient for a multitude of experiments which may be carried out in the future and which are impossible in the presence of an electron beam. The magnetic trapping mode thus represents a new opportunity for studying the physics of highly charged ions in regimes that have been previously inaccessible.

The delayed electron emission of negatively charged tungsten clusters has been investigated on a time scale from 1 to 500 ms. After being stored in a Penning trap clusters ions [Formula: see text] were heated via multiphoton absorption (hν=1.81 eV). In contrast to alkali and coinage metals no photofragmentation could be detected. Instead, for all cluster sizes studied so far only a decrease in the initial ion intensity as a function of time after excitation was observed. This decrease is not caused by ion loss from the trap, but has to be attributed to neutralization via delayed electron emission. The presented results strongly suggest that this process can be viewed as “thermionic emission” known from bulk-metal surfaces.

A Penning trap system has been set up for storing and investigating cluster ions over time ranges from microseconds up to minutes. This enables studies of cluster reactions with extremely low cross sections and the observation of their time dependence in a new regime. The ions are created externally by laser vaporization, cooled by adiabatic expansion of a supersonic beam, and injected into the Penning trap. Detection of reaction products is achieved by combining the advantages of two complementary approaches, viz. the high resolution of Fourier transform mass spectrometry and the high sensitivity of single-ion counting with a time-of-flight mass spectrometer. The performance of the apparatus is illustrated by results of recent cluster experiments.

An overview is given of experiments with stored metal cluster ions in a Penning trap system. The setup allows axial injection of clusters produced in an external source and a time-of-flight mass analysis of the reaction products after axial ejection. The system's options include the selection of stored ions, the manipulation of their orbits, addition of reactant and buffer gases and axial optical access for laser spectroscopic studies. As described by various examples, investigations have been made with respect to the development of trapping techniques and the characterization of metal clusters in terms of their physical and chemical properties.

Methods are being developed to analyze and control the ionic composition of a confined plasma with use of ion cyclotron modes. Resolving powers much higher than possible with time-of-flight analysis are achieved. Selected heating and removal of a given species from the plasma are demonstrated. The methods have been extended from singly charged ions confined in a Penning trap to very highly charged ions such as bare Kr36+ confined in an electron beam ion trap.

Fourier transform-ion cyclotron mass spectrometry has been applied to the study of highly charged ions produced and confined in an electron beam ion trap. Measurements of the relative ion abundance of hydrogenlike and bare krypton ions were made and compared to the abundance ratios determined with standard X-ray techniques. Good agreement was found establishing the reliability of the method as a new tool in highly charged ion research.

Small metal clusters were produced by laser desorption and transferred into a Penning trap. They were illuminated by a 20‐ns dye‐laser pulse and electronically excited. Relaxation channels were investigated in the case of positively charged gold and silver clusters evaporation of neutral atoms or dimers (depending on photon energy and number of cluster atoms) was observed. Photoabsorption cross section measurements of Au9+. For Au21+ yield a resonance similar to the one already known for Ag9+. For Au21+ and Ag21+ a delayed photofragmentation in the millisecond range has been observed.

In view of increasing use of large-core fiber-optic laser beam delivery systems, especially in high-resolution spectroscopic applications, we report experimental studies on unwanted spectral distortions arising from non-linear optical processes during the propagation of a narrow-band (<0.9 GHz, fwhm) pulsed (9.3 ns) dye laser beam through a large diameter (600 μm), step-index, pure silica core fiber. Large spectral broadening (100 GHz, fwhm) and cascaded stimulated Raman scattering (tilde; 11–13 orders), at low input powers were observed. Enhancement of the spectral distortions due to self-focusing of the input wave is qualitatively discussed. The spectral distortions could be suppressed considerably by disrupting self-focusing by external perturbations at various locations along the length of the fiber.

The dissociation channels of gold cluster ions Aun+ (2 ≤ n ≤ 23) have been investigated via collision induced dissociation in a Penning trap. Excited odd cluster ions with n ≤ 15 decay by evaporation of dimers, all others decay by monomer evaporation. Information on the binding energies is deduced from these dissociation channels.

Reactions between small gold cluster ions, Au1-4+, and N2O were studied in a Penning trap mass spectrometer. Gold clusters were produced by laser vaporization and injected into a Penning trap. After reaction times of 50-7000 ms the products were detected by time-of-flight mass spectrometry. For the major reaction channel, Au1,2+ + N2O --> Au1,2 N + NO+, rates of (0.9+/-0.1) x 10(-12) cm3 s-1 and (2.4+/-0.4) x 10(-12) cm3 s-1 were determined which are about a factor 500 below the collision rate. The corresponding activation energies for N2O decomposition were estimated to lie below 0.6 eV and 0.3 eV. Additional products with small branching ratios were detected, viz. the ions Au1O+, Au1N2O+, Au2N+, Au2NO+, Au2N2O+, Au3O+, Au3N2O+, and Au4N2O+. This indicates a preference for nitrogen-oxygen bond rupture in the case of Au1+ and Au3+, and for nitrogen-nitrogen bond rupture in the case of Au2+.

The stability of gold cluster ions Au n + (2≦n≦23) has been investigated via collision induced dissociation in a Penning trap. Threshold energies and dissociation channels have been determined. The cluster stability exhibits a pronounced odd — even alternation: Clusters with an odd number of atoms,n, are more stable than the even-numbered ones. Enhanced stabilities are found for Au 3 + , Au 9 + , and Au 19 + in accordance with the Clemenger-Nilsson and the deformed jellium model of delocalized valence electrons. Excited odd cluster ions withn≦15 predominantly decay by evaporation of dimers; all others decay by monomer evaporation. From the dissociation channels estimates of the binding energies are deduced.

A pulsed ion beam from an external source is injected into a Penning trap and accumulated by repeatedly lowering during ion capture to prevent the ions already captured from escaping. For the same reason the newly captured ions have to be cooled, which achieved by buffer gas collisions. To prevent radial on loss, the ions are exposed to azimuthal quadrupole excitation. By choosing the appropriate frequency (range) this method (selective quadrupole excitation assisted capture and centering (SQUEACE) allows a mass selection during the capture process and leads to a centering of those ions in the Penning trap. The multiple ion bunch capture results in a significant improvement in signal-to-noise ratio and a decrease in experiment duration.

The hyperfine structure splitting and the isotope shift in the λ=266 nm transition of Pt isotopes within the mass range 183 ≦A≦ 198 have been determined by Resonance Ionization Mass Spectroscopy (RIMS) in combination with Pulsed-Laser Induced Desorption (PLID). The Pt isotopes were obtained at the on-line isotope separator ISOLDE-3/CERN as daugthers of the primarily produced Hg isotopes. Magnetic moments, quadrupole moments, and changes in the mean-square charge radii are deduced and compared with results of a particle-triaxial rotor model and mean field calculations. Good agreement with experimental data (including nuclear level schemes and transition probabilities) can only be obtained if triaxial shape is admitted. The calculations yield a smooth transition in the shape of odd-A Pt nuclei from a slightly deformed, nearly oblate195Pt via triaxial197-187Pt to a strongly deformed nearly prolate177Pt.

A new cooling technique for heavy ions stored in a Penning trap has been developed. The axial and cyclotron motions are cooled by buffer gas collisions. The outward radial diffusion caused by the buffer gas is counteracted by an azimuthal quadrupole rf field at the sum frequency of the magnetron and cyclotron motions. A mass selectivity of 500 in the cooling is achieved while the axial energy distribution is observed to be in equilibrium with the buffer gas temperature (T = 300 K).

Doublet mass measurements of the isobars28Si3 and12C7 are performed by use of a Penning trap mass spectrometer and the Fourier transform ion cyclotron resonance (FT-ICR). The carbon and silicon cluster ions are produced by laser ablation. Results of these preliminary measurements are presented.