Absolute3 P o triple differential cross sections for electron-helium Wannier threshold ionization

The hyperfine structure sub-levels of the 5s5p³P₁ state of cadmium are populated coherently with a 35 ps light pulse. The coherence is detected in a second excitation step resulting in a modulation of the ionization probability. A third light pulse ionizes the atom. Differences in the H.F.S. of the odd isotopes are used to selectively enhance the ionization of one isotope. In a magnetic field the Zeeman splitting of the hyperfine structure causes an additional modulation. Measurements and a theoretical interpretation are given.     

Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.