Absolute ionization energies are typically measured for isolated atoms or molecules, whereas in solution, the corresponding oxidation or reduction potentials are not measured in isolation, but are measured relative to other half-cell potentials.  These relative potentials are referenced to a common electrode thereby establishing a ladder of relative thermochemical values.  The universally accepted �anchor� to this electrochemical series is the standard hydrogen electrode, which is assigned an arbitrary half-cell potential of exactly 0 V.  The absolute electrode potential has been the subject of both considerable interest and controversy, and even the concept of such a potential has given rise to heated debates.  Reduction enthalpies of isolated ions in aqueous nanodrops can be measured using an ion nanocalorimetry method in which the energy deposited into the nanodrop upon capture of an electron is determined from the number of water molecules that evaporate from the droplet.  In contrast to solution measurements, these gas-phase experiments are electron limiting so that reduction potentials of some ions that are not observed to undergo a one-electron reduction in water can be measured in these nanocalorimetry experiments.  Results for transition metal ions show that some ions for which a one-electron reduction has not been measured with conventional electrochemistry experiments, an absolute reduction potential can be measured using nanocalorimetry whereas for other metal ions, an ion-electron pair is formed.  For these later ions, the absolute solvation enthalpy of an electron can be obtained.  Progress on experimentally calibrating this nanocalorimetry method using light generated from lasers will be discussed, and a route to establishing an absolute electrochemical red-ox and ion solvation scale that is obtained entirely from experimental measurements will be presented.

Establishing an absolute electrochemical and ion solvation scale with mass spectrometry

248th National Meeting (2014)

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