Christopher S. Johnson

Experimental assessment of dynamic structural parameters for homogeneous and interfacial charge-transfer reactions: case studies based on time-dependent Raman scattering methods

Abstract The application of time-dependent scattering methodologies to dynamic structural problems involving charge transfer reactions is described. We show experimentally that a time-dependent analysis of resonance-enhanced Raman scattering can lead to a complete mode-by-mode description of the vibrational structural changes accompanying charge transfer and, therefore, a complete description of the vibrational activation barrier to charge transfer. (In other words, all force constants, all mode displacements, all bond-length displacements, and all individual energy components of the barrier can be determined.) The strategy is illustrated with case studies of internal (metal-to-ligand) charge transfer, ligand-bridged metal-to-metal charge transfer, outer-sphere charge transfer, and interfacial charge transfer.

Interface design based on standardized task models

Producing high-quality, comprehensible user intetices is a difficult, labor-intensive process that requires experience and judgment. In this paper, we describe an approach to assisting this process by using explicit models of the user’s task to drive the interface design process. The task model helps to ensure that the resulting interf%ce directly and transparently supports the user in performing his task. By crafting a library of standardized, reusable tasks and interface constructs, we believe it is possible to capture some of the design expertise and to amortize much of the labor required for building effective user interfaces.

Unexpected redox rectification by an electrochemically prepared iridium oxide electrode/aqueous acid interface

In highly acidic aqueous solutions, electrochemically prepared iridium oxide films behave as steady-state insulators and transient rectifiers towards the Ru(NH3)63+/2+ redox couple. In less acidic solutions the films show only partial transient rectification or else fully reversible transient behavior, together with Koutecky—Levich-type steady-state behavior. Experimental studies, as a function of Ru(NH3)63+ concentration, solution pH, film thickness, voltammetric sweep rate and electrode rotation rate, show that these unusual phenomena are related to: (1) transient uptake of Ru(NH3)63+, apparently in place of H+, during film-based Ir(IV/III) cycling; (2) Donnan exclusion of Ru(NH3)63+ from the reduced film under steady-state conditions; and/or (3) film-based diffusional inhibition of Ru(NH3)63+ reduction.