Aspects of low energy electron scattering--the role of temporary negative ions in dissociative electron attachment and in total scattering from laser pumped molecules, and orientation effects in electron impact excitation

An understanding of the formation and decay of temporary negative ions is essential in studies of the electronic excitation of atoms near threshold and the vibrational excitation and dissociation of molecules. For molecular targets, certain decay channels of the temporary negative ion are known to depend on the internal energy of the molecule. However, very little is known of the influence of the internal energy of the molecular target on the total scattering. For this purpose, the changes in the total electron scattering cross section of SF$\sb6$ when vibrationally pumped by a CO$\sb2$ laser are examined. Changes of both signs were observed in the cross section as a function of the electron impact energy. The energies at which the observed changes occur correspond to those at which the temporary negative ions states of SF$\sb6$ are formed. Measurement of the negative ion yield following electron attachment to several types of molecules was carried out to characterize the intermediate temporary negative ion. These studies in ammonia led to the assignment of the electronic configuration of the anion state responsible for the dissociative electron attachment yield as well as evidence for the nature of the electron correlation in this state. The effect of geometry on ion yield was examined in several chlorine bearing compounds in which the halogen atom could be positioned in or out of the $\pi$ nodal plane. A trapped electron technique is used to study the total inelastic cross sections in Ne, Ar, Kr, and Xe from onset to 2 eV above threshold. Finally, in a separate study, the time evolution of an excited state in an external magnetic field is demonstrated. The initial alignment of an excited atomic state, produced by electron impact parallel to a magnetic field, evolves into an orientation with finite angular momentum along the magnetic field direction and thus gives rise to a circularly polarized component in the radiation propagating parallel to the magnetic field