Fragmentation of α- and β-alanine molecules by ions at Bragg-peak energies

The interaction of keV He(+), He(2+), and O(5+) ions with isolated alpha and beta 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 H(3)(+) was found. The measured kinetic energies of ionic alanine fragments can be sufficient to induce secondary damage to DNA in a biological environment. (C) 2008 American Institute of Physics

Ionization and fragmentation modes of nucleobases after collisions with multiply charged ions

We studied multiply charged ion (MCI) induced ionization, excitation and fragmentation of the nucleobases uracil and thymine. Ions of different charge state at velocities between 0.2 and 0.4 atomic units were used as projectiles. By means of time-of-flight spectrometry of the collision products in a statistically representative mode as well as in triple coincidence mode, three different interaction types could be identified. Large impact parameters lead to "gentle'' ionization of the molecules, whereas in close collisions mainly multifragmentation occurs. This gives rise to a bimodal mass-spectrum as found in fullerene fragmentation studies. An additional two-body breakup channel leading to intermediate fragment sizes was found for both nucleobases. From the coincidence data, the kinetic energy release of this channel could be obtained

IONIZATION AND FRAGMENTATION OF ANTHRACENE UPON INTERACTION WITH keV PROTONS AND alpha PARTICLES

The interaction of keV ions with polyaromatic hydrocarbons is dominated by charge exchange and electronic stopping. We have studied the response of the polyaromatic hydrocarbon anthracene (C(14)H(10)) upon keV H(+) and He(2+) impact using high-resolution time-of-flight mass spectrometry. Extensive fragmentation into small C(n)H(m)(q+) as well as formation of up to triply charged parent ions is observed. Ab initio electron densities are used to calculate the molecular excitation due to electronic stopping. Fragment yields increase with the increase of electronic stopping as a function of projectile velocity. For equal electronic stopping, He(2+) is found to induce more fragmentation than H(+). The difference in fragmentation is concluded to be due to two electron processes, which are relevant channels only for He(2+)