M. Fogle

Electron-Impact Ionization of Be-like C III, N IV, and O V

We present recent measurements of absolute electron-impact ionization cross sections for Be-like C iii ,N iv, and O vformingLi-likeCiv,Nv,andOvi.Themeasurementsweretakenusingthecrossed-beamsapparatusatOakRidge National Laboratory. A gas cell beam attenuation method was used to independently measure the metastable fractions present in theion beams. The measuredionization cross sections were compared with calculations usingtheR-matrix with pseudostates and distorted-wave theoretical methods. Best agreement is found with the R-matrix with pseudostates cross sections results that account for the metastable fractions inferred from the gas attenuation measurements. We present a set of recommended rate coefficients for electron-impact single ionization from the ground state and metastable term of each ion. Subject headingg atomic data — atomic processes — methods: laboratory

Electron-impact dissociative excitation and ionization of N{sub 2}D{sup +}

Absolute cross sections for electron-impact dissociation of N{sub 2}D{sup +} producing N{sub 2}{sup +}, ND{sup +}, and N{sup +} ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N{sub 2}{sup +} production dominates. The N{sub 2}{sup +} + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas, and V. Zhaunerchyk, Phys. Rev. A 82, 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N{sub 2}{sup +}, ND{sup +}, and N{sup +} ion fragment production are comparable. The observance of the ND{sup +} and N{sup +} ion fragments indicate breaking of the N - N bond along certain dissociation channels.

Electron-impact dissociation of XH{sub 2}{sup +} (X=B, C, N, O, F): Absolute cross sections for production of XH{sup +} and X{sup +} fragment ions

Absolute cross sections for electron-impact dissociation of XH{sub 2}{sup +} (X= B, C, N, O, F) producing XH{sup +} and X{sup +} ion fragments were measured in the 3- to 100-eV range using a crossed-electron-ion beams technique. Dissociative excitation of BD{sub 2}{sup +} and CH{sub 2}{sup +} producing B{sup +} and C{sup +}, respectively, show a propensity toward a two-body dissociation while the remaining species all tend to show a three-body dissociation dynamic. The BD{sup +} and CH{sup +} dissociative excitation channels show a large resonant-type contribution to the cross sections at {approx}10 eV. For the X{sup +} fragment ion production cross sections, a clear dependence on the threshold energy, as it relates to the rate of rise in the cross section above threshold, is observed.

Electron-impact dissociation of CD{sub 3}{sup +} and CH{sub 3}{sup +} ions producing CD{sub 2}{sup +}, CH{sup +}, and C{sup +} fragment ions

Using a crossed electron-ion beams method, we measured absolute cross sections for electron-impact dissociation of the CD3+ molecular ions producing CD2+ fragment ions and CH3+ ions yielding CH+ and C+ fragment ions over a collision energy range from a few eV up to 100 eV. The total experimental uncertainties are about 12% at the maximum of the curves of cross sections (peak of the cross section, for the CH+ channel). The obtained results suggest important roles played by pre-dissociation of bound states in the production of both the CH+ and C+ fragment ions. Good agreement is found with other results reported for the CH+ fragment, but some differences are found for the CD2+ and C+.

Experiments on Interactions of Electrons with Molecular Ions in Fusion and Astrophysical Plasmas

Through beam‐beam experiments at the Multicharged Ion Research Facility (MIRF) at Oak Ridge National Laboratory (ORNL) and at the CRYRING heavy ion storage ring at Stockholm University, we are seeking to formulate a more complete picture of electron‐impact dissociation of molecular ions. These inelastic collisions play important roles in many low temperature plasmas such as in divertors of fusion devices and in astrophysical environments. An electron‐ion crossed beams experiment at ORNL investigates the dissociative excitation and dissociative ionization of molecular ions from a few eV up to 100 eV. Measurements on dissociative recombination (DR) experiments are made at CRYRING, where chemical branching fractions and fragmentation dynamics are studied. Taking advantage of a 250‐kV acceleration platform at the MIRF, a merged electron‐ion beams energy loss apparatus is employed to study DR down to zero energy. Recent results on the dissociation of molecular ions of importance in fusion and astrophysics are ...