Charge-state correlated cross sections for single- and multiple-electron removal processes (capture and ionization) in proton-H${}_2$O collisions are calculated by using the nonperturbative basis generator method adapted for ion-molecule collisions [Phys. Rev. A 80, 060702(R) (2009)]. The results are compared with experimental data for a wide range of impact energies spanning from 20 keV to several MeV. Single-electron removal probabilities in each molecular orbital are evaluated using the inclusive-probability formalism to predict the yields of charged fragments (H${}_2$O${}^{+}$, OH${}^{+}$, H${}^{+}$, O${}^{+}$) according to branching ratios that are valid at high impact energies. At intermediate and low energies, we calculate improved fragmentation cross sections that include the effects of multiple-electron removal processes. The resulting fragmentation yields agree with experiments at the 20$\%$–30$\%$ level even below 100 keV impact energy. DOI: http://dx.doi.org/10.1103/PhysRevA.85.052704 ©2012 American Physical Society

A quantum-mechanical approach to ion-molecule collisions is presented. It involves a separation of molecular geometry and collision dynamics and enables the use of the basis generator method developed for ion-atom collisions with relatively minor modifications. As a first application, we consider the $p{\text{-H}}_2\text{O}$ collision system in the impact energy range of 20–5000 keV, and we report total cross sections for net electron transfer and ionization. They are in remarkably good agreement with experimental data.

Projectile angular-differential cross sections for single-transfer and transfer excitation have been calculated with the two-center extension of the nonperturbative basis generator method for 5–200 keV proton-helium collisions. The calculations are based on the independent electron model, and the eikonal approximation has been used to extract angular-differential cross sections from impact-parameter-dependent transition amplitudes. The present results are compared with experimental and previous theoretical data where available. In particular, we consider the ratio of transfer excitation to single capture versus double excitation to single excitation at intermediate energies. An experimentally observed structure in this ratio at a scattering angle about 0.5 mrad is qualitatively reproduced, while a previous classical evaluation failed in this respect. Therefore, we conclude that this structure is caused by quantum mechanical heavy-particle-electron couplings.

In this work, we report experimental and theoretical ionization and electron-capture cross sections for single-, double- and triple-electron removal from ${\mathrm{H}}_2\mathrm{O}$ by ${\mathrm{Li}}^{3+}$ impact at energies ranging from 0.75 to 5.8 MeV. The experiment was carried out by selecting both the final charge state of the projectile and the ejected fragments in coincidence to obtain cross sections associated with ionization and electron-capture channels. The ionic fragments and the emitted electrons produced under single-collision conditions were collected by a time-of-flight spectrometer with single-hit (e.g., ${\mathrm{OH}}^{+}+{\mathrm{H}}^0)$ and double-hit events (e.g., ${\mathrm{OH}}^{+}+{\mathrm{H}}^{+})$ properly discriminated. For the one- and two-electron removal cases, the calculations based on the basis generator method for orbital propagation agree well with the experiment for most of the collision channels studied. Auger-electron emission after vacancy production in the inner $2a_1$ orbital of ${\mathrm{H}}_2\mathrm{O}$ is shown to have a substantial effect on the final charge-state distributions over the entire impact-energy interval.

The injection of energetic neutral particles into the plasma of magnetic confinement fusion reactors is a widely-accepted method for heating such plasmas; various types of neutral beam are also used for diagnostic purposes. Accurate atomic data are required to properly model beam penetration into the plasma and to interpret photoemission spectra from both the beam particles themselves (e.g. beam emission spectroscopy) and from plasma impurities with which they interact (e.g. charge exchange recombination spectroscopy). This paper reviews and compares theoretical methods for calculating ionization, excitation and charge exchange cross sections applied to several important processes relevant to neutral hydrogen beams, including H + Be⁴⁺ and H + H⁺. In particular, a new cross section for the proton-impact ionization of H (1s) is recommended which is significantly larger than that previously accepted at fusion-relevant energies. Coefficients for an empirical fit function to this cross section and to that of the first excited states of H are provided and uncertainties estimated. The propagation of uncertainties in this cross section in modeling codes under JET-like conditions has been studied and the newly-recommended values determined to have a significant effect on the predicted beam attenuation. In addition to accurate calculations of collisional atomic data, the use of these data in codes modeling beam penetration and photoemission for fusion-relevant plasma density and temperature profiles is discussed. In particular, the discrepancies in the modeling of impurities are reported. The present paper originates from a Coordinated Research Project (CRP) on the topic of fundamental atomic data for neutral beam modeling that the International Atomic Energy Agency (IAEA) ran from 2017 to 2022; this project brought together ten research groups in the fields of fusion plasma modeling and collisional cross section calculations. Data calculated during the CRP is summarized in an appendix and is available online in the IAEA’s atomic database, CollisionDB.