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.
Experimental and theoretical studies of one-electron capture in collisions of He 2+ ions with H 2 O molecules have been carried out in the range 0.025-12 keV amu −1 corresponding to typical solar wind velocities of 70-1523 km s −1 . Translational energy spectroscopy ͑TES͒, photon emission spectroscopy ͑PES͒, and fragment ion spectroscopy were employed to identify and quantify the collision mechanisms involved. Cross sections for selective single electron capture into n = 1, 2, and 3 states of the He + ion were obtained using TES while PES provided cross sections for capture into the He + ͑2p͒ and He + ͑3p͒ states. Our model calculations show that He + ͑n =2͒ and He + ͑n =3͒ formation proceeds via a single-electron process governed by the nucleus-electron interaction. In contrast, the He + ͑1s͒ formation mechanism involves an exothermic two-electron process driven by the electron-electron interaction, where the potential energy released by the electron capture is used to remove a second electron thereby resulting in fragmentation of the H 2 O molecule. This process is found to become increasingly important as the collision energy decreases. The experimental cross sections are found to be in reasonable agreement with cross sections calculated using the Demkov and Landau-Zener models.
Ion-induced fragmentation of H2O molecules was investigated experimentally by 3He2+ impact as a function of the energy in the range from 1 to 5 keV, as well as a function of the charge state of 20 keV 20Neq+ projectiles (q = 3 and 7). The fragments were detected in the angular range from 25° to 135° with respect to the incident beam direction. Particular emphasis is given to protons originating from collisions at large impact parameters involving a Coulomb explosion mechanism. Absolute cross sections dσ/dΩ, differential in the emission angle, are found to be anisotropic. Protons are preferentially emitted at angles near 90°, with cross sections being ∼50% larger than those at forward and backward angles. Possible mechanisms causing anisotropic emission of protons from fragmenting H2O are discussed.
The fragmentation in the collision system 3He2++H2O has been investigated experimentally at projectile energies ranging from 1 keV to 5 keV. The fragments were detected at angles from 25° to 130°. The experimental spectra exhibit two groups of peaks. The first one, which extends up to ∼30 eV, is interpreted in terms of a Coulomb explosion mechanism. A second group observed at higher energies, corresponds to fragments and scattered projectiles produced in quasi-binary collisions. In the analysis, particular attention is paid to these energetic ions. Absolute cross sections dσ/dΩ, differential in the observation angle, are found to be in good agreement with calculations assuming that the interaction of the screened nuclei is described by the ZBL (Ziegler, Biersack and Littmark) potential.
Angular distributions of recoiling He2+ and He+ ions following collisions of slow O5+ ions and He atoms were measured, for projectile energies in the range 100–2500 eV. The recoil ions were detected at angles from 20° to 130°. Two groups of peaks are clearly visible, corresponding to single and double electron capture. Highly energetic He2+ and He+ ions were observed at forward angles. It has already been shown in previous works on the C5+ and B5+ + He collisions that recoiling He+ targets mainly originate from a single electron capture on the n = 2 or 3 orbitals of the projectile, whereas He2+ ions are due to a double electron capture on 2ℓnℓ′(n ≥ 2) configurations. The population of such configurations is confirmed by our model calculations based on classical kinematics equations. From this model, charge exchange probabilities P (b), where b is the impact parameter, were deduced for the explored projectile energies. To explain the large kinetic energies for recoil targets, we had to invoke electron capture processes under small impact parameter conditions (b < 1 au). At 2500 eV, while the capture events occurring at large impact parameters are not detected in the present measurements, electron capture in collisions at small impact parameters is evidenced. At the lowest projectile energy (100 eV) we have access to the whole range of impact parameters. The contribution of small impact parameters is shown to be dominant at this energy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.