Fragmentation of high energy mass-selected ionic hydrogen clusters (original) (raw)
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Fragmentation of high-energy ionic hydrogen clusters by single collision with helium
International Journal of Mass Spectrometry and Ion Processes, 1994
Fragmentation of mass-selected 60-keV us'-Hz induced by single collision with helium has been studied for various cluster sizes (n = 9, 13,21,25 and 31). The absolute cross sections of the charged fragments Hi are measured fromp = 3 to n-2. The deduced mass distributions are markedly different to those obtained at lower collision energy (where molecular evaporation is mainly involved) due to a strong production of ionic fragments with a size of p/n (0.5. Moreover, the distributions for p/n 5 0.5 are found to have scaling properties and to follow a power law A-', where A is the normalized fragment mass (p/n) and T an exponent close to 2.6.
Physical Review A, 2006
Absolute dissociation cross sections are reported for H n + clusters of varied mass (n = 3, 5, …, 35) following collisions with He atoms at 60 keV / amu. Initial results have been published in a previous brief report for a smaller range of cluster sizes [Ouaskit et al., Phys. Rev. A 49, 1484 (1994)]. The present extended study includes further experimental results, reducing the statistical errors associated with the absolute cross sections. The previously suggested quasi-linear dependence of the H n + dissociation cross sections upon n is developed with reference to expected series of geometrical shells of H 2 molecules surrounding an H 3 + core. Recent calculations identify n = 9 as corresponding to the first closed H 2 shell [e.g. Štich et al., J. Chem. Phys. 107, 9482 (1997)]. Recurrence of the distinct characteristics observed in the dissociation cross section dependence upon cluster size around n = 9 provides the basis for the presently proposed subsequent closed shells at n = 15, 21, 27, and 33, in agreement with the calculations of Nagashima et al. [J. Phys. Chem. 96, 4294 (1992)].
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
Electron capture cross sections of hydrogen cluster ions H n colliding with atomic helium have been measured in a large range of cluster size (5 T n T 35) for the same velocity (1.5v 0 , 60 keV/u). While the electron capture cross section decreases from the H ion to the H 3 one, the cluster electron capture cross section is found to be independent of the cluster size and nearly equal to the capture cross section of the H 3 ion. Electron capture by hydrogen clusters on a helium atom is a process involving only the H 3 core of the cluster where the positive charge is localized. It appears that this very localized electron capture is not disturbed by the presence of molecules, up to sixteen, around the H 3 core.
Chemical Physics Letters, 1996
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Target fragmentation in intermediate energy heavy ion collisions
Nuclear Physics A, 1986
Radiochemical measurements of target fragment isobaric yields, excitation functions, fission cross sections, fragment angular distributions, etc. are presented for the interaction of 10-100 A MeV light (C-Ne) heavy ions with heavy targets (Sm-U). The characteristics of various aspects of target fragmentation are summarized and the possibility of a new "fast fission .. mechanis"m is suggested. r This report was done with support from the Department of Energy. Any conclusions or opinions expressed in this report represent solely those of the author(s) and not necessarily those of The Regents of the University of California, the Lawrence Berkeley Laboratory or the Department of Energy. Reference to a company or product name does not imply approval or recommendation of the product by the University of California or the U.S. Department of Energy to the exclusion of others that may be suitable.
Charge localization and fragmentation dynamics of ionized helium clusters
The Journal of Chemical Physics, 1998
The dynamics of He n ϩ , nϭ3-13, clusters formed by electron impact ionization of the neutral is studied theoretically using mixed quantum/classical dynamics by both mean-field and surface hopping methods. Potential energy surfaces and nonadiabatic couplings among them are determined from a semiempirical, minimal basis DIM Hamiltonian. The dynamics of hole hopping, hole localization, and cluster fragmentation are described through trajectory data. He 3 ϩ clusters, with initial conditions given by the zero-energy quantum distribution of nuclear coordinates, dissociate through two-channels, HeϩHeϩHe ϩ and HeϩHe 2 ϩ with relative yields of 20% and 80%. The motif of hole localization on a pair of atoms, and subsequent dissociation of the initial pair with hole hop to a new pair is observed in trimers, and repeats in larger clusters. In the larger clusters, hole hopping among He 2 pairs provides an additional, less important mechanism of charge migration. The coupled electronic-nuclear dynamics of triatomic units describes the mechanism of energy loss, by transfer of vibrational to translational energy. This leads to ejection of energetic neutral atoms as well as the ejection of He 2 ϩ prior to evaporative cooling of the cluster. He 2 ϩ is the exclusive charged unit produced in the fragmentation of He 13 ϩ clusters. In bulk He the same dynamics should lead to fast vibrational relaxation tϽ10 ps and formation of He 3 ϩ as the positive ion core.
On the projectile fragmentation in heavy-ion reactions at intermediate energies
Nucl. Phys. A 466 139, 1987
The two-body fragmentation of the projectile in the target field is described within a three-body dynamic model. Four types of reaction emerge: fusion at low energies and low impact parameters b, elastic and inelastic reactions at high b and two types of fragmentation in peripheral collisions. For high b the two projectile parts are emitted while for low 6 one fragment fuses with the target and only the other one can be detected. In the first case the part which has grazed the target has been strongly slackened and has a velocity of 0.7 V beam for small emission angles to 0.5 V beam for large angles. It might be a contribution to the relaxed fragment events detected at intermediate angles. In agreement with experimental data, the b2 window for this kind of fragmentation is very narrow for heavy quasi-projectiles and widens with decreasing masses. This model allows to reproduce semi-quantitatively the mass distribution of the quasi-projectiles, the position of the maximum in the one-and two-peak energy spectra and the relative importance of the two types of fragmentation.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2000
The energy distributions of H + fragments produced in 345 keV Xe 23+ +H 2 and 75 keV O 5+ +H 2 collisions have been investigated experimentally as a function of the detection angle. For both systems, the experiment shows strong deviations from the molecular Coulomb explosion. Two-and three-body model calculations have also been performed to understand the energy spectra. In the collisions involving the heaviest projectile Xe 23+ , the two-body calculations reproduce the experimental data satisfactorily, indicating that the recoil energy transferred to the target plays an important role in the fragment-energy distributions. On the other hand, for the system O 5+ +H 2 , the deviations between calculations and experiment suggest that the interaction between the outgoing projectile and each fragment plays the major role.