The Electron Affinity of Atomic Oxygen

Abstract

IN a recent communication, Morris and Schmeising¹ applied the empirical extrapolation of ionization potentials of isoelectronic ions to determine the binding energy of the O− ion (the atomic oxygen electron affinity). By extending the order of the extrapolation through eight isoelectronic ions (to S⁷+), they find a slightly higher value, 1.044 eV., than is found from the more usual quadratic extrapolation. Stating that experimental determinations of the electron affinity have given results in unresolved conflict, Morris and Schmeising refer to three discordant values. A value of about 2.2 eV. was obtained by a thermodynamic evaluation of the probability of attachment of electrons to atomic oxygen at a hot filament, and from electron impact studies undertaken originally to determine the dissociation energies of molecular nitrogen and carbon monoxide. The value of 1.48 eV. is given by the optical threshold for photodetachment from O− by Smith and Branscomb. The value of 1.05 eV., which coincides with Morris and Schmeising's extrapolation, was obtained by Schüler and Bingel from the analysis of a certain discrete band spectrum thought to be due to a transition between two bound states of OH−. (For the original references see Morris and Schmeising¹.) My purpose here is to resolve these apparent ambiguities.