In this paper we extend our previous study (Gianturco, F. A.; Raganelli, F.; Di Giacomo, F. Schneider, F. J. Phys. Chem. 1995, 99, 64) on selective vibrational excitations in proton-water scattering experiments (Friedrich, B.; Niedner, G.; Noll, M.; Toennies, J. P. J. Chem. Phys. 1987, 87, 5256) presenting further MRD-CI calculations of specific "cuts" of the relevant potential energy surfaces (PESs). On the basis of the existence of crossing and avoided crossing features between PES's correlated to the H + H2O+((X) over tilde) and H+ + H2O and to H+ + H2O and H + H2O+((A) over tilde) asymptotic systems, two partially different mechanisms are proposed for proton-water charge-transfer processes leading to H2O+((X) over tilde) or to H2O+((A) over tilde). The model general predictions on the behavior of the total average vibrational energy transfer in the two channels as a function of scattering angle are shown to favorably compare with the experimental results, as also do the theoretical predictions on the size for the charge-transfer cross sections sigma(CT)((X) over tilde) and sigma(CT)((A) over tilde) The computed potential energy curves (PECs) for two of the most important lines of approach of protons to water molecules are further analyzed by using a generalized Heitler-London approximation, thereby affording us a better understanding of the physical reasons behind the general shapes of such "cuts". On the basis of symmetry arguments, the existence of a toroidal region is then surmised, which encircles water in its molecular plane through which a proton is to pass in order for the charge-transfer process H+ + H2O --> H + H2O+((X) over tilde) to happen. The protonation of water, its nonadiabaticity and charge transfer aspects, and the dissociation channels of the bound oxonium are finally discussed, reinterpreting the computed PECs from these additional points of view.