The structure of small molecules with the Coulomb Explosion method

The content of this paper is divided into two parts: (1) achievements of the last two years in studying molecular ion structure with the aid of the newly developed Coulomb-Explosion (CE) method, and (2) the understanding of the modern CE data in terms of an invariant density of nuclear coordinates of the studied molecule

Coulomb explosion of 173-MeV HeH+ ions traversing carbon foils

The Coulomb explosion of 173-MeV HeH1 molecular ions traversing thin carbon foils has been measured for foil thicknesses ranging from 2 to 200 mg/cm2. In contrast with measurements at lower energies, the energy spectra for protons observed emerging in the incident beam direction show distinct components that correspond to the partner helium ions being in charge states 0, 1, and 2. From an analysis of the variation of the yields of these components as functions of the target thickness, we extract electron-loss cross sections that are in good agreement with theoretical estimates. ‘‘Wake effects’’ that increase with increasing target thickness are observed as asymmetries in the yields and energy shifts for ‘‘backward-going’’ as compared to ‘‘forward-going’’ protons

Rhetoric But Whose Reality? The Influence of Employability Messages on Employee Mobility Tactics and Work Group Identification

Over the last decade, employability has been presented by its advocates as the solution to employment uncertainty, and by its critics as a management rhetoric possessing little relevance to the experiences of most workers. This article suggests that while employability has failed to develop into a key research area, a deeper probing of its message is warranted. In particular, it is suggested that employability may have resonance with employees as workers rather than as employees of their immediate employing organisation. This demands a slightly different approach to studying employability than some other related phenomena such as employee commitment which has resonance only in relation to the employing organization. In adopting a social identity approach, the significance of the employability message is shown not only to lie in employees’ willingness to disassociate from their existing work groups and pursue individual mobility, but also in its capacity to undermine workers’ collective responses to grievances and unwanted organizational changes. A future research agenda is presented which highlights the need to address recent attempts to develop employability expectations among graduate career entrants, and for a closer critical engagement with management writings that attempt to justify the unnecessary espousal of the self development message

Physics with fast molecular-ion beams

Fast (MeV) molecular-ion beams provide a unique source of energetic projectile nuclei which are correlated in space and time. The recognition of this property has prompted several recent investigations of various aspects of the interactions of these ions with matter. High-resolution measurements on the fragments resulting from these interactions have already yielded a wealth of new information on such diverse topics as plasma oscillations in solids and stereochemical structures of molecular ions as well as a variety of atomic collision phenomena. The general features of several such experiments will be discussed and recent results will be presented

Interactions of fast atomic and molecular ions with matter

Brief discussions are presented of research performed in the following areas: microwave field ionization of fast Rydberg atoms; electric field ionization of foil-excited Rydberg states of fast heavy ions; post-foil interaction in foil-induced molecular dissociation; and angular distributions of foil-excited ions bearing inner shell vacancies. 19 references. (GHT

Interactions of fast atomic and molecular ions with matter

Argonne's 5-MV Dynamitron accelerator is used to study the interactions of fast (MeV) atomic and molecular ions with matter. A unique feature of the apparatus is the exceptionally high resolution, in angle and time-of-flight, obtained in detecting particles emerging from the target. New imaging detector systems have been developed which allow detection of multiparticle events consisting of up to 12 particles. The work has as its main objective a general study of the interactions of fast charged particles with matter, but with the emphasis on those aspects that take advantage of the unique features inherent in employing molecular-ion beams (e.g., the feature that each molecular ion incident upon a solid target forms a tight cluster of atomic ions that remain correlated in space and time as they penetrate the target). In particular, these techniques have allowed the direct determination of the geometrical structures of the molecular ions entering the target, providing the first direct measure of the fully correlated nuclear densities within small molecules

What can Coulomb explosions teach us about clusters

Although C/sub 3//sup +/ is considered to be the fundamental building block of the larger carbon clusters, the geometry of this molecule is unknown. Several authors have reported results of ab initio calculations in which the optimized geometry of the ion is deduced, assuming a linear configuration, in agreement with the structure of the neutral C/sub 3/ molecule. We report here the results of a series of measurements exploiting the Coulomb Explosion Method (CEM) to study the geometric structure of the C/sub 3//sup +/ ion. Our results indicate a cyclic structure for this ion. For comparison, measurements were also made of the carbon geometries of small hydrocarbon cations of the form C/sub 3/H/sub n//sup +/ (n = 1-4). Ring structures, of varying rigidities, are observed for all of these except C/sub 3/H/sub 4//sup +/ which exhibits a linear geometry. We also present results for doubly-charged species. 21 refs., 2 figs

MUPPATS: a multiparticle 3D imaging detector system

It has long been recognized that the foil-induced dissociation of fast molecular ions is a potentially powerful method to determine the stereochemical structures of the molecular projectiles. We have recently developed a detector system specifically designed for such experiments. The MUPPATS detector is a large-area multistep low pressure gas counter. The requirements of multiparticle detection with good position and time resolution leads to a rather complex data-readout and reduction scheme. The system relies on several state-of-the-art techniques, developed in high-energy physics during recent years, to dramatically reduce the cost of the MUPPATS detector. Preliminary results for several polyatomic molecular ions have already been obtained. Some new avenues of research opened up by this detector are also described

Model for charge state distributions of heavy Coulomb explosion fragment ions

We have conclusively demonstrated the systematic shift of the distributions of final charge states, for Coulomb explosion fragments compared to isotachic monatomic ion beams. This shift includes both an enhanced yield of lower charge states (below the equilibrium mean) concomitant with a decrease in the yield of charge states above the mean and thus essentially preserves the shapes of the distributions. From the trends of the data, it was shown that this shift is attributable to an enhanced electron capture probability for ions emerging from the target foil as spatially correlated diatomic clusters. A simple model was presented relating the charge state distributions measured for molecular-ion impact to the equilibrium distribution measured for the case of impact by a monatomic ion beam. This model describes the apparent nonequilibration of the molecular-ion charge state distributions as a simple consequence of electron capture cross sections dependent upon the internuclear separations of the exiting cluster fragments. Because this separation is large compared to the orbital radius of captured electrons, the enhancement of the electron capture cross sections can be treated as a weak perturbation of the potential at the position of the electron. Such an approximation allows the estimation of this enhancement. This model, though admittedly overly simplified, resolves the long-standing problem of understanding the distributions of final charge states when heavy diatomic molecular ions exit from solids