Absolute cross sections for fragmentation of water molecules by ${\mathrm{C}}^{3+}$ and ${\mathrm{O}}^{5+}$ ions over an energy region where the Bragg peak maximizes were measured for ionization, electron capture, and electron loss channels. A collision regime where ${\sigma }_{{\Sigma }_q{\mathrm{O}}^{q+}}\ge {\sigma }_{{\mathrm{H}}_2{\mathrm{O}}^{+}}$ was reached for the first time, producing large abundances of ${\mathrm{H}}^{+}$ and ${\mathrm{O}}^{+}$ fragments in comparison to proton impact. Our findings have straightforward implications in the subsequent fast chemistry at the ionization site and on the O production in the first stages of water radiolysis. An unexpected channel-independent relationship between the cross sections for the fragmentation products, which is also approximately independent of the particle type, energy, and charge state, is found. A model is presented to explain such behavior allowing the cross sections of all fragmentation products to be obtained from single and double electron removal cross sections.

• Received 22 October 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.043201