ELECTRONIC-STATE CHROMATOGRAPHY - APPLICATION TO 1ST-ROW TRANSITION-METAL IONS

Ion mobilities for first transition series atomic metal ions in helium have been measured. The mobilities of both ground-and excited-electronic-state ions were measured as a function of temperature. Very large differences in mobility (as much as 40%) were found for different electronic states of the same ion. The largest mobility differences were observed between electronic states with different electron configurations (i.e., 3d(n) and 3d(n-1)4s). Electronic states within the 3d(n-1)4s manifold of states have slightly differing mobilities, while differences in mobilities between states with 3d(n) configurations could not be resolved. These results are explained by differences in repulsion between the helium neutral and the ion 4s or 3d orbital electrons. Preliminary metal ion-helium clustering data support the proposed explanation. These large mobility differences, together with existing data showing the presence of certain electronic states, allow the quantitative determination of the principal electronic states present in the atomic metal ions. This, in turn, makes the realization of state-specific chemistry with these ions much easier. Deactivation of excited electronic states is also discussed. Only cases in which the excited electronic state has a Ar 3d(n) configuration and the ground state an Ar 3d(n-1)4s configuration are found to deactivate significantly in collisions with helium. This occurs in Mn+ and Fe+ and can be explained with a curve-crossing argument proposed by Armentrout.