Excitations from dissociative fragments produced inH++H2Ocollisions

Abstract

We report on photon emissions in the $200--800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ region resulting from collisions of $200\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ protons with ${\mathrm{H}}_{2}\mathrm{O}$. The most prominent features observed in the spectrum are the Balmer series of hydrogen and two OH molecular bands. Several less intense ${\mathrm{O}}^{+}$ as well as neutral O lines are also observed. The absolute photon emission cross sections of the major lines and bands were measured. The results indicate that a primary dissociation pathway involves the formation of ${\mathrm{H}}_{2}{\mathrm{O}}^{+}$ by removing a $1{b}_{2}$ electron. The unstable ${\mathrm{H}}_{2}{\mathrm{O}}^{+}$ ion further dissociates into ${\mathrm{H}}^{+}+\mathrm{O}\mathrm{H}$ or $\mathrm{O}{\mathrm{H}}^{+}+\mathrm{H}$. The dominant presence of neutral hydrogen lines and ${\mathrm{O}}^{+}$ lines leads to the conclusion that the subsequent dissociation of $\mathrm{O}{\mathrm{H}}^{+}$ into $\mathrm{H}+{\mathrm{O}}^{+}$ prevails over the other possible dissociation pathway leading to ${\mathrm{H}}^{+}$ and neutral oxygen fragments.