Production of Lyman Alpha Radiation in Ion-Atom Collisions

The absolute cross section as a function of incident ion energy has been measured for the production of Lyman alpha radiation (using an ${\mathrm{O}}_2$-filtered, iodine-filled Geiger counter as a detector) when ions impact on gases. The principal reactant pairs studied were: (${\mathrm{He}}^{+}$, ${\mathrm{H}}_2$), (${\mathrm{H}}_2^{+}$, He), (${\mathrm{H}}^{+}$, He), (${\mathrm{H}}^{+}$, ${\mathrm{H}}_2$), and (${\mathrm{H}}_2^{+}$, ${\mathrm{H}}_2$) in the energy range from about 100 to 6500 eV. Reaction mechanisms are discussed for each case. The data are found in most cases to agree qualitatively with the adiabatic hypothesis of Massey. Cross sections also were measured for the production of countable ultraviolet radiation with the following reactant pairs: (${\mathrm{H}}_3^{+}$, ${\mathrm{H}}_2$), (${\mathrm{H}}_3^{+}$, He), (${\mathrm{H}}^{+}$, ${\mathrm{N}}_2$), (${\mathrm{H}}_2^{+}$, ${\mathrm{N}}_2$), (${\mathrm{H}}_3^{+}$, ${\mathrm{N}}_2$), and (${\mathrm{He}}^{+}$, ${\mathrm{N}}_2$). No mechanisms are proposed for these cases. In an auxiliary experiment, the probability for producing ultraviolet radiation when ${\mathrm{H}}^{+}$ and ${\mathrm{H}}_2^{+}$ impinge on a metal surface was measured to be about 0.005 photon/ion.