Experimental Determination of the Electron Affinity of Fluorine

Abstract

Two methods are described for mass spectrometric determination of the electron affinities E(X) of electronegative atoms X. Both methods were used to determine the electron affinity of fluorine, E(F), the best measured value being E(F)=82.1±2.1 kcal/mole. In the first method the ratio of numbers of X^‐ negative ions to M⁺ positive ions emitted from a hot tungsten filament in MX salt vapor is measured. From this the equilibrium constant for the attachment reaction X+e^‐=X^‐, and hence E(X), may be calculated. In the second method, the difference in electron affinities, E(Y)‐E(X), is calculated from a measurement of the ratio of numbers of Y^‐ to X^‐ ions emitted from a hot filament surrounded by X_mY_n gas. Measurements were also made for the other halogens; these gave E(Cl)=86.6±2.0 kcal/mole, E(Br)=80.9±1.5 kcal/mole, and E(I)=73.2±1.7 kcal/mole.