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In the collision of electrons with molecules and molecular ions, excitation and dissociation are dominated by resonant processes, where the electron becomes temporarily trapped, changing the forces felt by the nuclei. In this paper, we will outline our method for treating these collision processes, where one or more resonant states exist. We separate the problem into two steps. First we carry out ab initio electron scattering calculations at fixed internuclear geometries to determine the resonant energy surfaces and the corresponding surface of autoionization widths, using the Complex Kohn variational method. These resonance positions and widths are then used as input to a dynamics study to determine the cross section and product distributions for the dissociation or excitation process. We will present results on a number of systems, including HCCH, HCN/HNC and HCCCN as examples of dissociative attachment, and H₂O⁺ for dissociative recombination.

We report vibrational excitation functions and angular distributions for electron scattering from the ground vibrational quantum (000), the bending vibrational quantum (010) and the unresolved first bending overtone (020) and symmetric stretch (100) modes of the ground-electronic state in hot (750 K) carbon dioxide (CO₂) molecules. The excitation function measurements were carried out at incident electron energies in the range of 1–9 eV, and at the electron scattering angles of 30°, 60°, 90° and 120°.

Electron collisions with N₂ are predominant components of the interaction between outer solar-system atmospheres and solar photons, solar wind, and magnetospheric electrons. Our collaboration between the Jet Propulsion Laboratory (JPL) and the California State University, Fullerton (CSUF), has devoted a significant effort over the last few years to improving the knowledge base of electron-N₂ excitation phenomena. Here, we highlight the lack of Franck-Condon behaviour in excitation of the Rydberg-valence states, using excitation of the C³Π_u state as a case in point. Further, we briefly introduce ongoing work measuring vibrationally-resolved emission cross sections for the Lyman-Birge-Hopfield (LBH) band system of the a¹Π_g (v') → X¹Σ⁺_g (v'') transitions. Specifically, we present preliminary results for the relative (3,0) emission cross section, which calls the currently accepted LBH shape function of Ajello and Shemansky (1985 J. Geophys. Res.-Space90 9845) into question.

We present a summary of recent progress in theoretical studies of low-energy dissociative electron attachment (DEA) to halogen molecules and polyatomic molecules based on the resonance R-matrix theory. It explains many observed features in DEA cross sections including low-energy behavior, threshold resonances and cusps. It also gives correct description of the temperature dependence of the attachment rate coefficients. More recently the theory was applied to two molecules of biological interest, formic acid and glycine. DEA mechanisms in these systems are very similar to those in hydrogen halides.

The electron stimulated desorption of anions from self-assembled monolayers of double stranded DNA is reported. Desorption of the oxygen and nitrogen containing anions O⁻, OH⁻, CN⁻, OCN⁻, and OCNH⁻ is induced by the impact of 0.1−20 eV electrons. The anion desorption yields, measured as a function of incident electron energy exhibit pronounced maxima that can be attributed to dissociative electron attachment (DEA) to basic DNA units. Above 15 eV, desorption is attributed to dipolar dissociation (DD). This study further indicates that electrons with energy as low as 2.5 ± 0.3 eV can not only cause damage to DNA but also produce fragments with considerable kinetic energy.

This contribution discusses possible effects of the plasma environment on dissociative recombination (DR) of two ion species, H⁺(H₂O)₄ and H₃⁺, for which afterglow measurements give larger recombination coefficients than beam experiments. This raises the question to what extent the apparent discrepancies reflect differing recombination mechanisms or are simply due other "errors" or "plasma complications". H⁺(H₂O)₄ recombination seems to be a case in which third-body effects are very strong. It also has been suggested that afterglow H₃⁺ recombination coefficients can be reconciled with the lower storage-ring and theoretical results by invoking third-body stabilization of initially formed high Rydberg states, but the estimates presented here indicate that one should be cautious in accepting such conclusions.

Careful analysis of multiple orbiting for collisions in classical mechancis shows that a larger impact parameter does not necessarily result in a larger orbiting separation. To take such possibilities into account, a new computer program has been developed for calculating the transport cross sections when a potential energy curve is supplied as a table of points. It is shown that the new program is superior to those used previously, but that it is not necessary to redo results obtained over the past 25 years in situations where transport cross sections were obtained to the requested accuracy by the previous programs.

The mobilities of a Li⁺ ion attached to 2-butanol in He gas have been measured using a drift tube mass spectrometer at room temperature. We observed a significant reduction in the mobilities over the entire range of E/N.