Asymmetrical dissociative ionization of N-2(+) and O-2(+) by electron impact

Absolute cross sections for electron impact formation of N2+ from N-2(+) and O-2(+) from O-2(+) have been measured in the energy range from below threshold to approximately 2000 eV. The animated crossed beams method has been employed. The cross sections at the maximum are found robe 8.4 x 10(-19) cm(2) and 12.1 x 10(-19) cm(2), respectively and the corresponding threshold energies are determined to be 43.7 +/- 0.5 eV and 36.8 +/- 0.5 eV. From an energy analysis of the collected dissociation products (N2+ and O2+), the maximum centre of mass energy available is found to be 13.0 +/- 1 eV and 14.6 +/- 1 eV, respectively

Ionization and dissociative ionization of CO+ by electron impact

Absolute cross sections for CO2+, C2+ and O2+ formation from CO+ by electron impact have been measured in the energy range from below the respective ionization or dissociative ionization thresholds to approximately 2500 eV. The animated crossed-beams method has been employed. The cross sections at the maximum are found to be 1.45 x 10(-17), 3.4 x 10(-19) and 1.3 x 10(-19) cm(2), for these reactions respectively and the corresponding threshold energies are determined to be 27.0 +/- 0.5, 42.3 +/- 1 and 48.1 +/- 1 eV. From an energy analysis of the collected dissociation products (C2+ and O2+) the maximum centre-of-mass energy available is found to be 12.1 +/- 1 and 7.2 +/- 1 eV and the width of the Franck-Condon transition band available is found to be 2.5 +/- 1 and 5 +/- 1 eV, respectively

Electron impact double ionization of C- and O- ions

Absolute cross section measurements for double ionization of C- and O- ions by electron impact are reported. The animated crossed beams method has been employed in the energy range from ionization threshold to approximately 2.5 keV. Present results are found to be smaller than the experimental result of Steidl et al (1995 Proc. 19th Int. Conf. Physics of Electronic and Atomic Collisions (Whistler) ed J B A Mitchell et al p 564). The role of slow positive ions trapped in the electron beam could explain the observed discrepancy. The study of double ionization processes along the fluorine isoelectronic sequence (for O-, Ne+ and Ar9+ ions) shows that the results for multiply charged ions are strongly lower than predicted by classical scaling. A systematic threshold energy shift is observed in the sequence and, for O-, the position of the cross section maximum is found to be at an unusually high energy. The autoionizing 1P state belonging to the (1s(2)2s2p(5)) configuration of atomic oxygen is clearly seen to contribute to the O+ signal above 23.7 eV. Other autoionizing states are also seen to play a role around the K-shell ionization threshold. The Bethe-plot of present data shows that the high energy behaviour of cross sections is dominated by the E-1, term for C-, while it is dominated by the logarithmic term for O-

Electron impact ionization and dissociation of CO2+ to C+ and O+

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

Separation of ions with the same charge to mass ratio from a collision experiment

Same atomic collision experiments lead to ions having identical q/m ratio, as well as average velocity, so that standard electric and magnetic analyzers are not able to identify them separately. This situation occurs;si for instance, in electron interaction with molecular monocations (A(2)(+)) producing A(2)(2+) (direct ionization) and A(+) (dissociation or dissociative ionization). Due to the transfer of internal energy to the kinetic energy of the fragments, they usually have a wider angular and energy distribution in the laboratory frame, compared to direct ionization. By use of a specially designed animated crossed beams apparatus, we are able to separate ionization and dissociation fragments. Here the preliminary results of cross sections measurements for electron impact on the N-2(2+) and N+ ions, is reported

Electron impact dissociation and ionization of N-2(+)

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

Absolute Cross-section Measurements for Electron-impact Ionization of Ar-7+

The first absolute cross section measurements for single and double electron impact ionization of sodium-like Ar7+ are reported. The animated crossed beams method has been employed in the energy range from threshold to 3000 eV. The measured cross sections for single ionization are higher than the theoretical and semi-empirical predictions by about 20-50%. This discrepancy has been associated with the contribution of the indirect ionization processes. The double ionization cross section is only 1% of the single one