351 J. Electroanal. Chem., 308 (1991) 351-356 Elsevier Sequoia S.A., Lausanne Preliminary note Estimation of the relaxation energy of solvated electrons in hexamethylphosphoric triamide solution from photon emission measurements Kei Murakoshi and Kohei Uosaki * Physical Chemistry Laboratory, Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060 (Japan) (Received 1 May 1991) INTRODUCTION The charge transfer reaction at an electrode/electrolyte interface is strongly affected by the interaction between the energetic states of the electrode surface and the electrolyte solution. Thus, to know the electronic energy distribution of donor/ acceptor in solution and that of electrode surface under the condition at which a reaction takes place is essential for a full understanding of the reaction process. However, the in situ determination of the electronic structures of interfaces is still very difficult in electrochemical systems. McIntyre and Sass have proposed a new technique which may be able to determine the electronic structure of the electrode and the solution [l-4]. In this technique, the photons emitted from a metal electrode are counted. The emission is considered to be due to radiative relaxation of excited states induced by electron injection from an electron donor, such as an organic anion radical, in solution into the empty electronic states in the metal, i.e., the inverse photoemission process. Thus, the emission spectrum is expected to reflect the electronic structure of the metal and the energy distribution of electron donor in solution, although the quantitative interpretation of the observed spectrum is difficult. We have recently applied this technique to the gold/acetonitrile interface and shown that the high energy threshold of the spectrum is determined as the difference between the electrode potential and the redox potential of the electron-in- jecting chemical species [5,6]. This means that the redox potential of the highest energy of the electron injection species can be determined from the high energy cm correspondence should be addressed. 0022-0728/91/$03.50 0 1991 - Elsevier Sequoia S.A.