Knowledge Bank

Negative and positive ions of ferrocene, nickelocene and magnesocene produced by collisions with monoenergenetic electrons have been studied. Positive ion appearance potentials have been determined for the products $(C10H10M)+$, $(C5H5M)+$ and $M+$, and the derived ionization potentials are compared with recent photoelectron data. In all cases cyclo-pentadienyl anions were produced at low electron energies; however, their cross sections of formation differ by orders of magnitude. The most striking feature of the negative ion studies was the observation of a long-lived (lifetime $>100\mu$sec) parent negative ion in nickelocene at thermal electron energies, and a second broader resonance centered at approximately one electron volt. The auto-detachment lifetime for the second resonance decreases from $60 \mu$ sec at 0.5 eV to 20 $\mu$ sec at 1.5 eV.