Kinetics ofHe(2S1)Using Resonance Ionization Spectroscopy

We have demonstrated that quantum selected populations of $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)$ can be converted completely to ionization by single-photon excitation to $\mathrm{He}\left(3\mathrm{}{}_{}{}^1{}_{}{}^{}P\right)$ followed by collision-induced associative ionization. For helium pressures between 15 and 100 Torr, saturation of ionization was observed whenever a tunable dye laser produced more than 0.1 J/pulse. Absolute numbers of $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)$ per ion pair formed from proton interaction and the decay rates of $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)$ support a recent energy-pathways model.