Time-of-Flight Energy and Mass Analysis of Metal-Helide Ions and Their Formation and Dissociation

An ion reaction-time amplification scheme is used to study field dissociation of Rh${\mathrm{He}}^{2+}$ formed by low-temperature field evaporation of Rh in He. Field dissociation of Rh${\mathrm{He}}^{2+}$ can occur by atomic tunneling within a few times ${10}^{-13\mathrm{}}$ s in a well-defined spatial zone of width ∼ 150 Å above the emitter surface. The time resolution of this measurement is as good as 20 fs.