Atomic and Molecular Physics

Atoms in highly excited Rydberg states are the focus of the research program of Barry Dunning, which investigates the behavior of matter at the interface between the quantum and classical worlds. Such atoms form the basis of experiments designed to control and manipulate atomic wave functions through application of a series of carefully designed electric field pulses whose duration is much shorter than the classical electron orbital period. This work is also permitting study of the behavior of impulsively driven or "kicked" atoms, which provide a new approach to studies of nonlinear dynamics and quantum and classical theories of chaos. Rydberg atoms are being used as a tool to probe electronmolecule interactions at ultra-low electron energies and to create new classes of weakly-bound negative ion species. The interaction of Rydberg atoms with surfaces is being investigated to better understand electron tunneling processes at surfaces, which form the basis of many practical surface analytical techniques.

In conjunction with King Walters, Dunning has pioneered a powerful array of spectroscopies based on spin-polarized electron, ion and atom beam techniques for probing surface geometric, electronic and magnetic properties and the dynamics of particle-surface interactions and to investigate the surface magnetic properties of bulk materials and thin film structures.

The focus of the research program of Bernard Lindsay and Ronald Stebbings is atomic collision processes of interest to aeronomic modelers and to NASA. Recent experiments have included the first measurements of differential charge transfer cross sections for an atomic oxygen target and a technique has been developed to measure state-selected differential charge transfer cross sections for oxygen ion projectiles. A number of highly quantitative electron-impact ionization studies have also been performed.

Ion distributions from electon impact on CF₄

One example is 160 eV electron impact on CF₄. Arrival positions and time-of-flight distributions of ions produced are shown in the figure. Each ion is identified by its flight time, the time between initiation of the extraction pulse and its arrival at the detectort. The position axis indicates the displacement of the ions perpendicular to the axis of the ionizing electron beam and gives some qualitative information about their relative kinetic energies.