Physics Colloquium: Kerry Hipps, Department of Chemistry, Washington State University
Monday, April 2 2012 at 4:00 PM
Location: EP 209
Physics Colloquium, with Kerry Hipps, department of chemistry, Washington State University, titled “Single Molecule Imaging of Oxygenation of Cobalt Octaethylporphyrin at the Solution/Solid Interface: Thermodynamics from Microscopy,” will occurApril 2 at 4 p.m. in EP 209.
Abstract: Basic concepts relating to STM imaging will be presented. Examples of STM images dominated by molecular electronic structure will be presented. For the first time, the pressure and temperature dependence of a chemical reaction at the solid solution interface is studied by STM and thermodynamic data is derived. In particular, the STM is used to study the reversible binding of O2 with cobalt(II) octaethylporphyrin (CoOEP) supported on highly oriented pyrolytic graphite (HOPG) at the phenyloctane/CoOEP/HOPG interface. The adsorption is shown to follow the Langmuir isotherm with P1/2 = 2,940 Torr. Over the temperature range of 20ºC to 40ºC it was found that DeltaHP = -87±10 kJ/mole and DeltaSP = 339±30 J/K-mol. The enthalpy and entropy changes are larger than expected based on solution phase reactions, and possible origins of these differences are discussed. The big surprise here is the presence of any O2 binding at room temperature, since CoOEP is not expected to bind O2 in fluid solution. The stability of the bound oxygen is attributed to charge donation from the graphite substrate to the cobalt, thereby stabilizing the polarized Co-O2 bonding. We report the surface unit cell for CoOEP on HOPG in phenyloctane to be A = (1.48±0.1)n nm, B = (1.42±0.1)m nm, and alpha = 52±4º, where n and m are unknown non-zero non-negative integers.