O. Heber

3-D imaging of binary dissociation events induced by heavy ion impact

Abstract Dissociation of CO molecules induced by 96 MeV Ar ions is being studied by simultaneously measuring the times of flight and the positions of the dissociation product ions. The position information is obtained using optical methods, thus overcoming the pile-up problem associated with measurements in which the position is determined using microchannel plate detectors with resistive anodes. For each dissociation event the velocity components of both ions are determined and used to deduce the released kinetic energy and the angular distribution. Preliminary results are shown for the dissociation of CO2+ into C+ and O+.

Recoil-ion kinetic energies for 96 MeV Ar collisions

Abstract The kinetic energies of He, Ne, and Ar recoil-ions produced in single collisions with 96 MeV Ar 4+ and Ar 15+ projectiles have been determined from high resolution time-of-flight measurements. They were found to vary from the ambient thermal energy for charge 1 recoil-ions to 5 eV for Ar 11+ recoil-ions. Average impact parameters were deduced from these results.

Two-fragment coincidence studies of molecular coulomb explosions induced by heavy ion impact

Abstract Time-of-flight (TOF) spectroscopy was used to study the ionic species produced in collisions of 40 MeV Ar13+ with molecular oxygen. Ions from the dissociation of molecular ions having charges as high as 10 + were observed. The flight times of the first ion and the difference in flight times between the first and second ions of binary dissociation events were recorded event-by-event, thereby retaining their correlation. Off-line sorting of the data provided TOF and time difference spectra containing well resolved peaks associated with each of the charge division pairs produced in the dissociation process.

Multiple ionization of He, Ne, and Ar by high velocity N7+ ions

The yields of He, Ne, and Ar recoil ions produced in collisions with 10–40 MeV/amu N7+ projectiles were measured by the time-of-flight technique. The ratio of the yields for double and single ionization of He and Ne were found to be higher than predicted by theoretical and semiempirical calculations. The role of electron correlation in multiple ionization was assessed by comparing the experimental data for Ne and Ar with the results of an independent electron approximation analysis.

Cross sections for Ar recoil ion production by 1 MeV/amu Oq+ (q = 2–8)

Abstract Cross sections for the production of recoil ions of Ar 1+ through Ar 10+ in collisions with 1 MeV/amu O 2+ through O 8+ ions have been measured using the time-of-flight (TOP) method. Postcollision charge state analysis of the projectile was performed to distinguish between events involving pure ionization ( q = 2–8), one-electron loss ( q = 2–6), two-electron loss ( q = 2–4), one-electron capture ( q = 3–8) and two-electron capture ( q = 5–8). The total direct ionization cross section was found to increase as q 1.5 . The electron capture cross sections also increased as a function of q , while at the same time the cross sections for electron loss decreased. Both of these processes exhibit a steeper q dependence than the pure ionization process. The charge state distributions are bell shaped for the electron capture process and for the electron loss process at high q . For electron loss at low q the distributions are similar to those for the pure ionization process.