Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to 4π and superior momentum resolutions around a few per cent of an atomic unit (a.u.) are typically reached in state-of-the art machines, so-called reaction-microscopes. Evolving from recoil-ion and cold target recoil-ion momentum spectroscopy (COLTRIMS), reaction-microscopes—the `bubble chambers of atomic physics'—mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields. This paper concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of high-intensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using reaction-microscopes. Third, for electron and ion-impact, the investigation of two-electron reactions has matured to a state such that the first fully differential cross sections (FDCSs) are reported. Fourth, comprehensive sets of FDCSs for single ionization of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is briefly envisaged.

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Recoil-ion and electron momentum spectroscopy: reaction-microscopes

Collective electronic excitations at metal surfaces are well known to play a key role in a wide spectrum of science, ranging from physics and materials science to biology. Here we focus on a theoretical description of the many-body dynamical electronic response of solids, which underlines the existence of various collective electronic excitations at metal surfaces, such as the conventional surface plasmon, multipole plasmons and the recently predicted acoustic surface plasmon. We also review existing calculations, experimental measurements and applications.

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Theory of surface plasmons and surface-plasmon polaritons

The motion of energetic charged particles inside a monocrystalline solid can be strongly influenced by channeling and blocking effects. The present article reviews the theory, the experimental studies, and some of the applications of these effects. The coverage of the published literature extends through June 1973.

Channeling and related effects in the motion of charged particles through crystals

Energy levels of A = 21−44 nuclei (V)

We review the theory of the electromagnetic interactions between rapidly moving charged particles and the matter through which they pass. The emphasis will be on very massive electric ($\ensuremath{-}100\ensuremath{\le}{Z}_{1}100$) and magnetic ($|g|=137e \mathrm{and} \frac{137e}{2}$) particles moving with relativistic velocities ($\ensuremath{\beta}g0.2$, $\ensuremath{\gamma}l100$). Consideration will be given to both the stopping power of the projectile and to the response of the absorbing medium to the excitation caused by the projectile.

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Theoretical and experimental aspects of the energy loss of relativistic heavily ionizing particles

A theoretical description is given of the polarization charge-density distribution induced in a solid by the passage of a fast charged particle. The stopping power of the solid (including the effects of close collisions) is well accounted for by the braking effect of the polarization charges. Calculations based on this model for the polarization give good agreement with the results of recent experiments on the dissociation of fast molecular ions in foils. (AIP)

Polarization induced in a solid by the passage of fast charged particles

Ionization and multifragmentation have been observed in C[sub 60] molecules bombarded by Xe[sup 35+] and Xe[sup 18+] ions with energies in the range 420--625 MeV. The c.m. energies exceeded those used in previous studies by several orders of magnitude. We present the observed mass distribution of positively charged fragments together with a theoretical model indicating that the total interaction cross section contains roughly equal contributions from (a) excitation of the giant plasmon resonance, and (b) large-energy-transfer processes that lead to multiple fragmentation of the molecule.

Ionization and Multifragmentation of C 60 by High-Energy, Highly Charged Xe Ions

The authors report measurements of the joint distributions in energy and angle for fragments arising from the dissociation of 1.2-MeV ${\mathrm{H}}_{2}^{+}$ and 3.0-MeV He${\mathrm{H}}^{+}$ in thin carbon foils and in a variety of gases at several pressures. From the foil measurements the distribution of initial internuclear separations in the incident projectiles is derived. These distributions are then used in conjunction with the results for gas targets to determine the role of excited electronic states of the projectile in collisionally induced dissociation. Finally, it is shown how these states also play a vital role in some other phenomena that occur in the interactions of fast molecular ions with foils.

Role of excited electronic states in the interactions of fast (MeV) molecular ions with solids and gases

Three different measurements on the structure of the H/sub 3//sup +/ molecular ion are reported. The measurements all make use of a new technique: the foil-induced dissociation of a fast molecular-ion beam. It is shown that the structure is equilaterally triangular in shape. The most probable length of side of the triangle is determined by the three measurements to be 0.97 +- 0.03 A, 0.95 +- 0.06 A, and 1.2 +- 0.2 A, respectively.

Donald S. Gemmell

Papers

Channeling and related effects in the motion of charged particles through crystals

Polarization induced in a solid by the passage of fast charged particles

Ionization and Multifragmentation of C 60 by High-Energy, Highly Charged Xe Ions

Role of excited electronic states in the interactions of fast (MeV) molecular ions with solids and gases

Experimental determination of the structure of H 3