Post-field ionization of singly charged rhodium: An experimental and theoretical study

Differential energy distributions are shown of field-evaporated ${\mathrm{Rh}}^{+}$ and ${\mathrm{Rh}}^{2+}$ ions. These spectra have been obtained using a magnetic-sector-field mass spectrometer. Experimental evidence of the occurrence of post-field ionization is presented. This post-field ionization is a process where an initially desorbed ${\mathrm{Rh}}^{+}$ ion loses a further electron by ordinary field ionization while traveling away from the rhodium field-emitter surface. The experimental results are compared with calculations using a three-dimensional version of the WKB approximation of the tunneling probability of the valence electron for the desorbing ${\mathrm{Rh}}^{+}$ ion. A reasonable agreement between experimental and theoretical data is obtained by including image-force interactions for the tunneling barrier.