Showing papers by "H. G. Berry published in 1996"

Ionization and fragmentation of C60 by highly charged, high-energy xenon ions.

Abstract: ${\mathrm{C}}_{60}$ vapor was bombarded by $^{136}\mathrm{Xe}^{35+}$ and $^{136}\mathrm{Xe}^{18+}$ ions in the energy range 420--625 MeV to study the various ionization and fragmentation processes that occur. Since the center-of-mass energies used in this work exceeded those of previous studies by several orders of magnitude, new excitation and dissociation modes were expected and indeed found. Positive ions were extracted from the interaction region and their times of flight were measured both singly and in coincidence with other ionic fragments. A wide range of stable charge states and cluster sizes from monatomic carbon up to ${\mathrm{C}}_{60}$ was observed. Even-numbered carbon fragments dominated the heavier mass range but both even and odd carbon numbers occurred at lower masses. Evidence was found for three qualitatively different ionization and fragmentation channels suggesting different ranges of collision impact parameters: ionization of the parent ${\mathrm{C}}_{60}$ molecule, loss of even numbers of carbon atoms, and ``multifragmentation'' into many small fragments. This latter mode included the production of singly charged ${\mathrm{C}}_{\mathit{n}}^{+}$ fragments with all values of n being observed from n=1 up to at least n=19. We interpret our results in terms of a theoretical model that indicates that the total interaction cross section contains comparable contributions from (a) excitation of the giant dipole plasmon resonance, and (b) large-energy-transfer processes that lead to multiple fragmentation of the molecule. The distribution of fragment cluster masses for n\ensuremath{\lesssim}20 is reproduced by a ``percolation theory'' description analogous to that used to describe multifragmentation of nuclei by high-energy protons. \textcopyright{} 1996 The American Physical Society.

The X-ray photoabsorption spectrum of potassium near the K-edge

Abstract: The authors have used a heat-pipe target in an X-ray beam to obtain photoabsorption spectra of potassium at the K- and KM-edges, in the photon energy range 3,600 to 3,650 eV. Preliminary identifications of most of the peaks observed are made using Dirac Hartree-Fock calculations. They compare these results with those obtained previously in closed-shell rare gas absorption spectra.

The VUV spectrum from fast heavy-ion induced excitation of

Abstract: We have measured the spectrum of vacuum ultraviolet radiation (500 - 1700 A) arising from the impact of 625 MeV xenon ions with . The spectral features are due primarily to emission from neutral and ionized carbon atoms. These photons mask sensitivity to either the giant dipole resonance or to excited dimers. We compare with data obtained in collisions of xenon ions with methane and isobutane. Decay times of several of the lines were also measured. Some of the lines persist for times long compared to the lifetimes of the corresponding states in neutral and ionized carbon.