The Emission of Negative Ions under the Bombardment of Positive Ions

The results which Sawyer obtained from the reflection of lithium ions from reflectors of platinum foil and nickel crystal deposited on tungsten, indicated two distinct angles at which reflection occurs more strongly than at other angles, one coming nearly at the angle of specular reflection as found by Read and Gurney, and the other which appeared only at relatively high voltages, at an angle approximately normal to the reflecting surface. Experiments made by reflecting the lithium ions from a metal surface in a field free space gave the bundle at the specular angle as before, but no trace of a bundle at the normal to the surface could be found. When a field is applied so as to retard reflected positive ions there was evidence of negative emission coming from the target under the bombardment of lithium ions. A magnetic analysis system was set up to determine the nature of the negative charges. Negative fluorine, chlorine, oxygen and sulphur ions were obtained by bombarding NaF, Ca${\mathrm{F}}_2$; NaCl, CaO, PbS and oxide-coated vacuum tube filaments. Clean metal targets of platinum, gold, aluminum, tantalum, nickel, and tungsten were found to emit electrons and the negative ions $\mathrm{H}_1^{}{}_{}{}^{-}$, $\mathrm{H}_2^{}{}_{}{}^{-}$, O${\mathrm{H}}^{-}$, and ${\mathrm{Cl}}^{-}$ with traces of what is probably ${\mathrm{N}}^{-}$ and LiO${\mathrm{H}}^{-}$. The strongest bundles were the first four which indicate that water-vapor molecules were broken up into their components.