Formation of excited H by impact of 5-30-keV ${\mathrm{H}}_1^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$ ions on metal surfaces

When 5- to 30-keV ${\mathrm{H}}_1^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$ are incident on Mo, Cu, or stainless-steel targets, a small fraction are backscattered in a neutral excited state. These particles subsequently decay and the emission can be observed as Doppler-broadened spectral lines. Measurements of the total Balmer-$\beta$ line intensity are presented as a function of incoming projectile energy. It is found that ${\mathrm{H}}_2^{+}$ and ${\mathrm{H}}_3^{+}$ projectiles at energy $E$ behave the same as two or three protons at energy $\frac{E}{2}$ or $\frac{E}{3}$, respectively. The energy dependence of the total intensity down to a projectile energy of 1.67 keV is consistent with a model which includes radiationless deexcitation at the surface.