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Ionisation and ion-induced fragmentation of tetraphenyl iron (III) porphyrin chloride (FeTPPCl) molecules have been studied after slow collisions (v∼ 0.2 a.u.) with multiply charged ions (O3+, Ar8+). Intact molecules and large fragments are observed in charge states up to q=4. For q=1, the intact molecule is the most abundant species, in particular, when projectiles in higher charge states are used. When the internal energy of the singly charged ion is increased by the energy transfer during the collision, the singly charged system de-excites by the emission of a neutral Cl-atom, a free electron or possibly a negative Cl anion. The processes are observed as direct as well as delayed processes on a μs-time scale. For q=2 to 4 the loss of the Cl-atom and some phenyl groups becomes more likely due to the lower stability and the larger energy transfer. The charge state distribution of atomic fragments is found to be very different, in particular, when Cq+ and Clq+ ions are compared. In the first case mainly singly charged ions are detected, whereas in the second case ions in charge states up to q=6 are observed with high intensities. These phenomena are discussed in terms of the intramolecular charge mobility. [ABSTRACT FROM AUTHOR]

We have measured total and coincident (with outgoing charge-state analyzed projectiles) ionization and fragmentation spectra of C60 and C70 following collisions with Xe4+ and Kr4+ at v = 0.06 a.u. Intact positive fullerene ions in charge states up to five (C60 5+ and C70 5+) are produced with both projectiles and for Kr4++C70 collisions we even observe a small C70 6+ peak. The C60/70-2m 3+ (m=1–7) intensity distributions are predominantly associated with the stabilization of three electrons on the projectile (s=3) and are significantly different for Xe4+- and Kr4+-projectiles. On the other hand, we find remarkable similarities in the C3 +-C11 + multi-fragmentation pattern regardless of projectile species (mass) although they are associated with closer encounters in which the projectile is fully neutralized (s=4). Simple Monte Carlo calculations of nuclear and electronic loss processes show that both these contributions are very similar in glancing Xe4++C60 and Kr4++C60 collisions, suggesting that frontal (and more violent) collisions are strongly suppressed under the present experimental conditions. Nevertheless it is surprising that the more distant collisions (s=3) are projectile mass dependent, while the closer collisions (s=4) are not. This indicates that this simple approach (although it reproduces more advanced quantum mechanical calculations for slow collisions with singly charged atomic ions rather well) is not valid for a comprehensive description of the energy transfer processes in the present collision systems involving projectiles of higher charge states. [ABSTRACT FROM AUTHOR]

Measurements of the cluster size (n) distribution of secondary (UOx)+n ions from sputtering of uranium dioxide (UO2) by Ne8+, Ar8+ and Xeq+ ions (q=10, 23) at fixed kinetic energy (81 keV) have been performed with a time-of-flight mass spectrometer. The cluster ion yields Y follow a power law Y(n)~nd with -2.1

We have investigated the time dependence of the fragmentation of protonated amino acids stored at 22 keV in the electrostatic ring ELISA. The ions were produced in an electrospray source and after bunching in a quadrupole trap they were excited by collisions in a Ne gas. As in earlier studies of metal clusters and fullerenes produced in "hot" ion sources we find that the dissociation of metastable molecules follows approximately a 1/t decay law until a time r after which the yield falls off much more rapidly. We interpret this reduction as a result of radiative cooling with a characteristic cooling time, τc ... Gr, where G is the magnitude of the exponent in an Arrhenius expression for the rate of the dominant fragmentation process. The values of τ obtained from fits to the data are in the range 9-17 ms corresponding to cooling times of a few hundred milliseconds, in good accord with the expected rate of cooling by emission from IR-active vibrations. The power-law behaviour for t < τ varies somewhat between the different amino acids, with powers between -0.9 and -1.1. We argue that this may be due to a competition between fragmentation channels with different Arrhenius parameters. [ABSTRACT FROM AUTHOR]

Highly charged sodium clusters produced in collisions between neutral clusters and multiply charged ions are formed within a large range of temperatures and fissilities, and identified by means of a high-resolution reflectron-type time-of-flight mass spectrometer ( m/δm ≈ 14000). The limit of stability of these charged clusters is experimentally investigated, and the time-of-flight spectra are compared with theoretical spectra based on Monte-Carlo simulations. The results indicate that the maximum fissility (X) of stable clusters is approaching the Rayleigh limit (X = 1) for larger clusters sizes. It is mainly limited by the initial neutral cluster temperature ( T ≈ 100 K) and the energy transfer in the ionizing collision. In addition, the comparison between the measured and simulated spectra suggests for high cluster charges a multi-fragmentation process, in which most of charge is emitted, creating low charged residual cluster ions. [ABSTRACT FROM AUTHOR]

An experiment to measure the strong interaction width (Γ1s) and shift (ℇ1s) of the ground state of pionic hydrogen (π-p), in order to determine the isospin separated scattering lengths (a+ and a-) with a relative accuracy of better than 10-2, has been undertaken at the Paul Scherrer Institute (PSI). This measurement is based on high-precision X-ray spectroscopy of the np→1s transitions pionic hydrogen (π-p). A preliminary analysis of the data taken in December 2000 is presented. [ABSTRACT FROM AUTHOR]

The determination of atomic lifetimes offers the possibility to investigate various aspects of the atomic structure. In the case of helium-like 197Au with nuclear spin 3/2, due to hyperfine-quenching, one can determine the 23P0–23P1 fine-structure splitting from the lifetime measurement of the metastable 23P0 state. This lifetime has been measured at the GSI accelerator facility with the beam-foil time-of-flight technique and has taken advantage of particle-X-ray coincidences using a charge state spectrometer in conjuction with a newly developed CVD-diamond particle detector. A preliminary analysis has given a value of 22.45±0.66 ps for the lifetime of the 23P0 state in helium-like gold. This is in good agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

Crystal spectrometry and absorption edge technique have the capability to overcome the gap in accuracy between experiment and theory in the strong field domain of QED. New results are presented which indicate the capacity of these methods to measure the energies of X-rays emitted by highly charged heavy ions at modern storage rings with a precision sensitive to second order corrections to the Lambshift in H-like very heavy ions. [ABSTRACT FROM AUTHOR]

A new experiment for a high-precision measurement of the pion mass at a 1 ppm level is presented. It combines an improved cyclotron trap that produces pionic and muonic atoms in a small volume with a doubly focusing crystal spectrometer to measure the corresponding exotic X-ray transitions with high accuracy and a novel type of CCD detector. The muonic X-rays lines serve as highly accurate calibration lines. The measurement has been accomplished recently. A detailed analysis of the data is on the way. [ABSTRACT FROM AUTHOR]