Time-of-flight-based mass analysis of charged water fragments have been used to measure the dissociative and the nondissociative reaction pathways of water formed during collisions with $15\text{to}100\mathrm{keV}$ and $500\text{to}3500\mathrm{keV}$ ${\mathrm{H}}^{+}$ projectiles and with $8\text{to}100\mathrm{keV}$ ${\mathrm{H}}^0$ projectiles. The fragmentation pathways resulting from the ionization and the electron capture collisions with the incident ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ projectiles, as well as collisions involving projectile electron loss by the incident ${\mathrm{H}}^0$ projectiles, were separately recorded by detecting the target product ions in coincidence with either the ejected target electrons or the charge-analyzed projectiles. The fragmentation profile shows that at high collision energies the ionization of water arises mainly through outer shell processes. At lower energies valence electron capture and ionization dominate and transfer ionization leads to substantially different fragmentation patterns. ${\mathrm{H}}^0$ and ${\mathrm{H}}^{+}$ projectiles are found to be equally efficient at ionizing the water molecule. These results are of particular interest to workers in astrophysics and those involved in cancer therapy with heavy particle ion beams.

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The dissociative photoionization of the chloroform and chloroform-d molecules has been studied in the valence region and around the chlorine 2p edge. Time-of-flight mass spectrometry in the coincidence mode-namely, photoelectron-photoion coincidence (PEPICO)-was employed. He I lamp and tunable synchrotron radiation were used as light sources. Total and partial ion yields have been recorded as a function of the photon energy. Singly, doubly, and triply ionized species have been observed below (195 eV), on (201 eV), and above (230 eV) the Cl 2p resonances. A definite degree of site-selective fragmentation was observed at the Cl 2p resonance as the relative contributions of several ionic species were seen to go through a maximum at 201 eV. At the same time all stable doubly charged ions were also observed at 198 eV (below the 2p resonances), resulting from direct ionization processes. Isotopic substitution is shown to provide a very efficient means of improving the mass resolution and assignment of unresolved peaks in spectra of CHCl(3), particularly for those fragments differing by a hydrogen atom. It is suggested that ultrafast fragmentation of the system following 2p excitation to a strongly antibonding state contributes to the large amount of Cl(+) observed in the PEPICO spectrum measured at 201 eV. Kinetic energy distributions were determined for the H(+), D(+), and Cl(+) fragments.

Cross sections for the processes of projectile electron loss and single and double capture of ${\mathrm{C}}^{3+}$ and ${\mathrm{O}}^{5+}$ projectile ions impinging on He, Ne, Ar, Kr, and Xe targets were measured in the energy range of 1.0–3.5 MeV. The measured cross sections present a strong saturation as the target atomic number increases, for all the systems and collision channels studied. The single-capture data are compared with calculations based on a semiclassical model and on the eikonal approximation, both presenting a good general agreement with the experiment. In the case of electron loss, the observed saturation is in accordance with previous measurements for ${\mathrm{He}}^{+}$ projectiles, and is present in the first-order calculations for the antiscreening contribution but not in those for the screening. This is due to the fact that, for heavy target atoms, the screening mode can be highly nonperturbative. Calculations for the screening contribution to the electron loss, based on the free-collision model, together with first-order results for the antiscreening, are compared with the experimental data, presenting good agreement in most cases. However, this comparison also shows that one has to include other competitive channels in order to give a better description of the collision.

Absolute multiple-ionization cross sections, ${\sigma }^{q+},$ of He $\mathrm{}(q=1,2\mathrm{}),$ Ne $(q=1,2,$ and 3), Ar $(q=1,2,$ and 3), Kr $(q=1,2,$ and 3), and Xe $(q=1,2,3,$ and 4) atoms have been determined for interactions with ${\mathrm{He}}^{+}$ ions in the 1.0–3.5-MeV impact energy range. Special care was taken to obtain the slow recoil-ion detection efficiencies, by measuring the recoil ions in coincidence with the ${\mathrm{C}}^{3+}$ capture channel and comparing these results with absolute single measurements. Comparison is made with the data available in the literature. The present results are in good agreement with the previously published data in the case of the helium target, but some nonsystematic discrepancies appear for heavier targets.

Absolute, total, single- and multiple-electron-loss cross sections are measured for $1.4\text{−}\mathrm{MeV}∕\mathrm{u}{\mathrm{U}}^{4,6,10+}$ ions colliding with neon and argon atoms and nitrogen molecules. It is found that the cross sections all have the same dependence on the number of electrons lost and that multiplying the cross sections by the initial number of electrons in the $6s$, $6p$, and $5f$ shells yields good agreement between the different projectiles. By combining the present data with previous measurements made at the same velocity, it is shown that the scaled cross sections slowly decrease in magnitude for incoming charge states between 1 and 10, whereas the cross sections for higher-charge-state ions fall off much more rapidly.