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In general, radiation-induced fragmentation of small amino acids is governed by the cleavage of the C-C(α) bond. We present results obtained with 300 keV Xe(20+) ions that allow molecules (glycine and valine) to be ionised at large distances without appreciable energy transfer. Also in the present case, the C-C(α) bond turns out to be the weakest link and hence its scission is the dominant fragmentation channel. Intact ionised molecules are observed with very low intensities. When the molecules are embedded in a cluster of amino acids, a protective effect of the environment is observed. The fragmentation pattern changes: the C-C(α) bond becomes more protected and stable amino acid cations are observed as fragments of the molecular clusters. Evidently, the molecular cluster acts as a "buffer" for the excess energy, capable of rapidly redistributing excess energy and charge., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The results from an experimental study of bare and microsolvated peptide monocations in high-energy collisions with cesium vapor are reported. Neutral radicals form after electron capture from cesium, which decay by H loss, NH(3) loss, or N-C(alpha) bond cleavage into characteristic z(*) and c fragments. The neutral fragments are converted into negatively charged species in a second collision with cesium and are identified by means of mass spectrometry. For protonated GA (G = glycine, A = alanine), the branching ratio between NH(3) loss and N-C(alpha) bond cleavage is found to strongly depend on the molecule attached (H(2)O, CH(3)CN, CH(3)OH, and 18-crown-6 ether (CE)). Addition of H(2)O and CH(3)OH increases this ratio whereas CH(3)CN and CE decrease it. For protonated AAA ([AAA+H](+)), a similar effect is observed with methanol, while the ratio between the z(1) and z(2) fragment peaks remains unchanged for the bare and microsolvated species. Density functional theory calculations reveal that in the case of [GA+H](+)(CE), the singly occupied molecular orbital is located mainly on the amide group in accordance with the experimental results.

A large number of studies are devoted to the investigation of the biomolecular ionization and fragmentation dynamics underlying biological radiation damage. Most of these studies have been based on gas-phase collisions with isolated DNA building blocks. The radiobiological significance of these studies is often questioned because of the lack of a chemical environment. To clarify this aspect, we studied interactions of keV ions with isolated nucleobases and with nucleobase clusters by means of coincidence time-of-flight spectrometry. Significant changes already show up in the molecular fragmentation patterns of very small clusters.

Metal–ligand cluster ions are structurally characterized by means of gas-phase infrared multiple photon dissociation spectroscopy. The mass-selected complexes consist of one or two metal cations M3+ (M = Al, Fe, or Ru) and two to five anionic bidentate acetylacetonate ligands. Experimental IR spectra are compared with different density functional theory calculations, namely, PBE/TZVP, B3LYP/6-31G*, and M06/6-31+G**. Frequency analysis was also performed at different levels, namely, scaled static harmonic and unscaled static anharmonic, or with ab initio molecular dynamics simulations at the PBE/TZVP level. All methods lead to simulated spectra that fit rather well with experimental data, and the spectral red shifts of several main bands, in the 1200 cm−1–1800 cm−1 range, are sensitive to the strength of the metal–ligand interaction and to the spin state of the ion. Due to the rigidity of those complexes, first principles molecular dynamics calculations provide spectra similar to that produced by static calculations that are already able to catch the main spectral signatures using harmonic calculations at the B3LYP/6-31G* level. [ABSTRACT FROM AUTHOR]

We find that the most stable fullerene isomers, C70-C94, form efficiently in close-to central collisions between keV atomic ions and weakly bound clusters of more than 15 C60-molecules. We observe extraordinarily high yields of C70 and marked preferences for C78 and C84. Larger even-size carbon molecules, C96-C180, follow a smooth log-normal (statistical) intensity distribution. Measurements of kinetic energies indicate that C70-C94 mainly are formed by coalescence reactions between small carbon molecules and C60, while Cn with n≥96 are due to self-assembly (of small molecules) and shrinking hot giant fullerenes. [ABSTRACT FROM AUTHOR]

The interaction of keV He+, He2+, and O5+ ions with isolated α and β isomers of the amino acid alanine was studied by means of high resolution coincidence time-of-flight mass spectrometry. We observed a strong isomer dependence of characteristic fragmentation channels which manifests in strongly altered branching ratios. Despite the ultrashort initial perturbation by the incoming ion, evidence for molecular rearrangement leading to the formation of H3+ was found. The measured kinetic energies of ionic alanine fragments can be sufficient to induce secondary damage to DNA in a biological environment. [ABSTRACT FROM AUTHOR]

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 + 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]11 + 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]

Clusters of C60 fullerenes are (multi)-ionised in collisions with O5+ projectiles at a collision energy of 100 keV. The dominant fragmentation channels are analysed by time-of-flight mass spectrometry for different cluster size distributions. Singly charged ${\rm C}^+_{60}$, ions are found to be the dominant fragments, in 25% connected with the loss of one or more C2-units. This result is explained by the large charge mobility in fullerene clusters. Doubly charged fragments, in form of ${\rm C}^{2+}_{60}$ and ${\rm C}^{2+}_{60-2m}$, contribute to the observed spectrum with less than 5–10% only and are mainly attributed to the fragmentation of dimers. Singly charged small carbon clusters in the size range n = 7 to 19 are formed with low kinetic energies indicating the importance of thermal dissociation processes. The present experiments confirm earlier conclusions on the charge mobility in fullerene clusters. [ABSTRACT FROM AUTHOR]

Clusters of C60 fullerenes are (multi)-ionised in collisions with O5+ projectiles at a collision energy of 100 keV. The dominant fragmentation channels are analysed by time-of-flight mass spectrometry for different cluster size distributions. Singly charged ${\rm C}^+_{60}$, ions are found to be the dominant fragments, in 25% connected with the loss of one or more C2-units. This result is explained by the large charge mobility in fullerene clusters. Doubly charged fragments, in form of ${\rm C}^{2+}_{60}$ and ${\rm C}^{2+}_{60-2m}$, contribute to the observed spectrum with less than 5–10% only and are mainly attributed to the fragmentation of dimers. Singly charged small carbon clusters in the size range n = 7 to 19 are formed with low kinetic energies indicating the importance of thermal dissociation processes. The present experiments confirm earlier conclusions on the charge mobility in fullerene clusters. [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

Single crystal graphite was irradiated by slow, highly charged ions. The modification of the surface structure was studied by means of Low-Energy Electron Diffraction. The observed damage cross section increases with the potential energy, i.e . the charge state of the incident ion, at a constant kinetic energy. The potential energy is more efficient for the damage production than the kinetic energy by more than a factor of twenty. Comparison with earlier results hints to a strong link between early electron creation and later target atom rearrangement. With increasing ion fluence, the initially large-scale single crystal is first transformed into μ m-sized crystals, before complete amorphisation takes place. [ABSTRACT FROM AUTHOR]

Abstract: The accelerator facilities of GANIL allow studying ion–surface collisions in a wide range of projectile velocities. On the one hand, high velocity heavy ions (MeV/u) where the electronic energy loss is dominant (electronic sputtering), and on the other hand, low velocity highly charged ions (keV/q) are available. In the latter case, nuclear stopping (elastic collision cascades) is more important. Possibly, further effects related to the high projectile charge and corresponding high potential energy can occur (potential sputtering). We use a combination of imaging techniques (XY) and time-of-flight (TOF) spectroscopy to measure the complete velocity vector of emitted secondary ions. We present results on energy and angular distributions of 7Li+ (atomic ions) sputtered from a LiF crystal by Ca17+ (9MeV/u) and Xe21+ (17keV/q =350keV) ions. The energy distributions differ strongly thus clearly showing that the material responds differently to energy deposition by purely electronic stopping (high velocity projectiles) and slow highly charged ions. We also compare the angular distributions of emitted Li+ ions and neutrals in the electronic stopping regime. [Copyright &y& Elsevier]

Abstract: A system of two crystal spectrometers for accurate wavelength measurements of hard X-rays emitted by heavy ions in flight is presently being completed. The configuration is working in the focusing compensated asymmetric laue (FOCAL) mode along with high performance two-dimensional position sensitive micro-strip Ge detectors. Recent tests of the spectrometer have been performed securing quantitatively spectral resolving power and efficiency predicted by numerical simulations. For the proposed application, nearly perfect Silicon single crystals need to be bent cylindrically using a precision crystal-bending device, close to the limit where they start to break. [Copyright &y& Elsevier]