COLLISIONAL ALIGNMENT AND ORIENTATION OF ATOMIC OUTER SHELLS .2. QUASI-MOLECULAR EXCITATION, AND BEYOND

We present a comprehensive and critical review on atomic alignment and orientation after collisional excitation including a full reevaluatio n and discussion of data published to date in the literature. The pres ent Vol. II focuses on the quasimolecular low-energy regime in ion-ato m and atom-atom processes. The discussion centers on experimental and theoretical data for planar scattering geometry in which the alignment and orientation parameters are determined as a function of scattering angle (particle-photon coincidence or scattering from laser-excited a toms, the so-called third-generation of experiments). In addition, ali gnment studies with cylindrical symmetry (second-generation experiment s) and integral cross sections (first-generation experiments) are also discussed wherever this clarifies the understanding of the relevant p rocesses. A unified set of parameters is used with reference to the so -called natural coordinate frame (having its z-axis perpendicular to t he collision plane): the angular momentum transfer L perpendicular to, the alignment angle gamma, the linear polarization P+ and the symmetr y-changing probability rho(00). This parametrization allows one an int uitive interpretation of these otherwise somewhat abstract quantities. After reviewing the theoretical framework the individual model system s are described, starting with excitation and charge transfer in the g enuine one-electron system H++H and ending with He++Rg (Rg = raregas a tom) collisions involving many electrons and demonstrating the explici t influence of spin-orbit coupling. In several appendices a compilatio n of the relevant classical deflection functions and many useful formu lae for the interpretation of alignment and orientation parameters are reported.