Using resonant two-photon ionization of metastable rare gas atoms Rg(mp 5(m + 1)s 3P2,0) in a collimated beam by two transverse cw dye lasers, we have performed a comprehensive high resolution study of the odd Rg(ns',J =0,1) autoionization resonances of all the heavier rare gases Rg--Ne, Ar, Kr and Xe. In this way, we have determined the variation of the nearly n-independent reduced resonance widths F, = n*3. Fn (n*= effective quantum number) with atomic size andfor the first time -with the angular momentum J for all Rg. The reduced widths for the Rg(ns', J = 1) resonances vary by about a factor of three, being lowest for Ne(371 cm -1) and largest for Kr(l185 cm-1). Compared to J = 1, the Rg(ns', J =0) resonances are three times narrower for Ne, but up to two times broader for Ar, Kr, and Xe. The results of ab initio calculations for the widths are reported, in which the relevant transition matrix elements are carefully evaluated. Good overall agreement of the calculated widths with the experimental data is achieved. For Rg(ns', J = 0), the first order s'-d coupling amplitude provides a satisfactory description only for Rg = Ne, whereas for Rg = Ar-Xe, correlation effects are important. For Rg(ns', J = 1), the additional amplitudes due to s'-d exchange coupling and due to s'-s decay are found to be of varying importance with atomic number. Destructive interference between the different amplitudes and the influence of Rg(ns', J = i)-Rg(nd', J --t) coupling are responsible for the fact that the (ns', J = 1) resonances are narrower than the (ns', J = 0) resonances for Ar, Kr, and Xe.

The alignment, ordering, and rotation of elongated granular particles was studied in shear flow. The time evolution of the orientation of a large number of particles was monitored in laboratory experiments by particle tracking using optical imaging and x-ray computed tomography. The experiments were complemented by discrete element simulations. The particles develop an orientational order. In the steady state the time- and ensemble-averaged direction of the main axis of the particles encloses a small angle with the streamlines. This shear alignment angle is independent of the applied shear rate, and it decreases with increasing grain aspect ratio. At the grain level the steady state is characterized by a net rotation of the particles, as dictated by the shear flow. The distribution of particle rotational velocities was measured both in the steady state and also during the initial transients. The average rotation speed of particles with their long axis perpendicular to the shear alignment angle is larger, while shear aligned particles rotate slower. The ratio of this fast/slow rotation increases with particle aspect ratio. During the initial transient starting from an unaligned initial condition, particles having an orientation just beyond the shear alignment angle rotate opposite to the direction dictated by the shear flow.

Granular gases are convenient model systems to investigate the statistical physics of nonequilibrium systems. In the literature, one finds numerous theoretical predictions, but only few experiments. We study a weakly excited dilute gas of rods, confined in a cuboid container in microgravity during a suborbital rocket flight. With respect to a gas of spherical grains at comparable filling fraction, the mean free path is considerably reduced. This guarantees a dominance of grain-grain collisions over grain-wall collisions. No clustering was observed, unlike in similar experiments with spherical grains. Rod positions and orientations were determined and tracked. Translational and rotational velocity distributions are non-Gaussian. Equipartition of kinetic energy between translations and rotations is violated.

We introduce smectic freely floating microbubbles and report their unusual dynamic properties. In equilibrium, they form minimal surfaces like soap films, but shape transformations of closed smectic membranes not in contact with menisci involve complex layer rearrangements. Very small distortions of the spherical equilibrium shape can relax by damped oscillations, driven by surface tension. Larger film area changes require the creation and motion of islands and layer dislocations. Then, film area changes are slow compared to natural oscillation frequencies. Quasistationary intermediate shapes evolve on the time scale of dislocation dynamics. These shape transformations are reminiscent of vesicles, in which the surface tension is effectively zero. We prepare smectic shells from collapsing catenoids and analyze their behavior with optical highspeed imaging.

Simple model calculations have been performed to gain new insight into the dynamics of the electron transfer process; for BC=SF6, our results at tow n(5<_n< 10) suggest that internal energy conversion in the Coulombic complex Ne ÷ -S F g is important for the formation of the detected ions.