Single- and multiple-electron processes in water molecules colliding with proton beams

Single- and multiple-electron removal processes (ionization, capture and transfer-ionization) from water molecules by the impact of protons have been studied. A prior version of the three-body continuum distorted wave-eikonal initial state (3B-CDW-EIS) approximation within the independent electron approximation is used to calculate transition probabilities as a function of the impact parameter and consequently pure and net absolute cross sections for the collisions under consideration. A unitarization procedure is employed to avoid possible overestimation of the 3B-CDW-EIS single-particle impact parameter probabilities at intermediate collision energies. Multiple-electron transitions are determined using a statistical multinomial distribution. A critical analysis of the validity of this type of distribution for describing pure single-electron processes is presented. The results are compared with other theoretical calculations and available experimental data at impact energies from 50 keV to 5 MeV. New physical insights into the reactions studied are introduced.