We present a study into the collision-induced dissociation (possibly including electron stripping) of O-3(+) and N-3(+) with rest gas molecules (predominantly H-2) in the heavy-ion storage ring CRYRING. The projectile ions had kinetic energies of 1.96 MeV (O-3(+)) and 2.25 MeV (N-3(+)) and from the experimental data we could derive the relative importance of the channels that produce at least one neutral product fragment. The dominant type of fragmentation for both ions involves the production of a single neutral fragment, namely an individual atom. We also find pronounced dissimilarities when comparing the O-3(+) and N-3(+) results, which we link to the stronger chemical bonds in the nitrogen system.

Absolute cross sections for heavy ion fragment production due to electron-impact dissociation of XH2+ (X = B, C, N, O, F), N2D+ and O3+ have been investigated with the crossed electron-ion beams technique in the energy range 3 – 100 eV. This energy regime covers the dissociative excitation and ionization processes. Two and three-body dissociation channels are observed in these systems and marked resonant-like structure is also observed in the dissociative excitation channels of some systems. It is unclear if direct excitation or resonant capture processes lead to these enhanced dissociative excitation cross sections.

Absolute cross sections for electron-impact dissociation of N2D+ producing N-2(+), ND+, and N+ 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-2(+) production dominates. The N-2(+) + 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-2(+), ND+, and N+ ion fragment production are comparable. The observance of the ND+ and N+ ion fragments indicate breaking of the N-N bond along certain dissociation channels.

Absolute cross sections for electron-impact dissociation of XH2+ (X = B, C, N, O, F) producing XH+ and X+ ion fragments were measured in the 3- to 100-eV range using a crossed-electron-ion beams technique. Dissociative excitation of BD2+ and CH2+ producing B+ and C+, respectively, show a propensity toward a two-body dissociation while the remaining species all tend to show a three-body dissociation dynamic. The BD+ and CH+ dissociative excitation channels show a large resonant-type contribution to the cross sections at similar to 10eV. For the X+ 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.

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+.

We present recent measurements of absolute electron-impact ionization cross sections for Be-like C III, N IV, and O V forming Li- like C IV, N V, and O VI. The measurements were taken using the crossed-beams apparatus at Oak Ridge National Laboratory. A gas cell beam attenuation method was used to independently measure the metastable fractions present in the ion beams. The measured ionization cross sections were compared with calculations using the R-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.

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 presented.

Absolute cross sections for electron-impact dissociation of CH2+ producing CH+ and C+ fragment ions were measured in the 3-100 eV range using a crossed electron-ion beams technique with total uncertainties of about 11% near the cross section peak. The cross sections are nearly identical for energies above 15 eV, but they are dramatically different at lower energies. The CH+ channel exhibits a strong peak rising from an observed threshold of about 6 eV; the C+ channel is relatively flat down to the lowest measured energy. Ionization cross sections for the CH2+ ion are also presented.

Absolute cross sections for electron-impact dissociation of D13CO+ ions have been measured over a collision energy range from 4 to 100 eV with a crossed electron–ion beams method. Total experimental uncertainties are about 16% near the cross section peak. The role of resonant and direct dissociative excitation for energies below 21 eV is discussed in light of the energy levels and photo-dissociation cross sections of the HCO+ formyl cation predicted by ab initio multi-reference configuration interaction calculations.

The paper reports an investigation of the dissociative recombination of PD2+ at the heavy-ion storage ring CRYRING. The absolute cross-section has been measured as a function of centre-of-mass energy ranging from 1 meV to 0.1 eV. The experiment performed has shown the dissociative recombination of PD2+ to be dominated by three-body break-up, with a branching ratio of about 78%. Competition between the available three-body channels producing the ground state, P(S-4), and the. first two excited states, P(D-2) and P(P-2), is observed. The formation of the first excited state dominates over the other two almost equally probable channels with about 75% of all three-body events. The results indicate that the kinetic energy released in the three-body break- up of PD2+ is randomly shared between the deuterium atoms. The intra-molecular angle on dissociation has also been investigated. A comparative analysis of the dissociative recombination dynamics for the two isovalent systems, PD2+ and NH2+, is undertaken.

Absolute cross sections for electron-impact dissociation of D13CO+ ions have been measured over a collision energy range from 4 to 100 eV with a crossed electron–ion beams method. Total experimental uncertainties are about 16% near the cross section peak. The role of resonant and direct dissociative excitation for energies below 21 eV is discussed in light of the energy levels and photo-dissociation cross sections of the HCO+ formyl cation predicted by ab initio multi-reference configuration interaction calculations.

The paper reports an investigation of the dissociative recombination of at the heavy-ion storage ring CRYRING. The absolute cross-section has been measured as a function of centre-of-mass energy ...

First absolute cross sections for electron impact single ionization of H3O+, HD2O+ and D3O+ and for dissociative excitation (DE) producing H+ and D+ are reported. The animated crossed electron-ion beam method has been employed in the energy range from threshold to 2500 eV. The maxima of these cross sections are found to be unusually small (<1 x 10(-17) cm(2)). The ionization threshold energies are determined to be 24.7 +/- 0.5, 24.4 +/- 0.5 and 24.0 +/- 0.5 eV for H3O+, HD2O+ and D3O+, respectively. The observed DE threshold energies lie in the range 10-12.5 eV and the maximum kinetic energies released are between 3 and 4 eV. Significant differences are observed between the results obtained for the three isotopomers.

Absolute cross sections for electron impact ionization and dissociation of CO2+ to form C+ and O+ fragments are measured in the energy range from threshold to 2500 eV. The animated crossed-beams method has been employed. The ionization cross section shows a maximum of 4.79 x 10(-17) cm(2) at 130 eV and the corresponding threshold is found in good agreement with previous measurements. Both dissociation cross sections are shown to exhibit wide plateaux which are of the same order of magnitude. In addition, these cross sections almost coincide above 100 eV. The threshold energy and kinetic energy released are determined for both the production of C+ and O+. They are found in good agreement with the previously published data obtained in electron impact ionization experiments of neutral CO2.

Absolute cross sections for electron impact ionization, dissociative excitation (DE) and dissociative ionization of N-2(+) ions are measured in the energy range from threshold to 2500 eV. The animated crossed electron-ion beam method has been employed. The individual contributions of ionization products (N-2(2+)) and dissociation fragments (N+), which have both identical mass-to-charge ratio and average velocity, are deduced from the analysis of product velocity distributions. Particular attention was paid to determining the transmission efficiency for dissociation fragments, since their collection was incomplete during the measurements. Threshold energies and kinetic energy released to dissociation fragments are measured. The role of states contributing to different reactions is discussed. For DE, the present results are found to be much smaller than the results of Peterson et al (1998). For ionization (single and dissociative), a satisfactory agreement with their result is obtained as well as with the prediction of Kim et al (2000) obtained in the binary-encounter Bethe approximation.