The Heat of Dissociation of CO and the Electron Affinity of O

Abstract

An apparatus previously described has been employed in a study of the dissociation produced by primary electron impact in CO and ${\mathrm{O}}_{2}$. The processes studied in ${\mathrm{O}}_{2}$ are ${\mathrm{O}}_{2}^{\ensuremath{-}}$\ensuremath{\rightarrow}${\mathrm{O}}^{\ensuremath{-}}$+O at 2.9 v and ${\mathrm{O}}_{2}^{\ensuremath{-}}$\ensuremath{\rightarrow}${\mathrm{O}}^{\ensuremath{-}}$+O* at 12.0 v with an estimated accuracy of \ifmmode\pm\else\textpm\fi{}0.2 v. These figures refer to the potential energy of the dissociation products, the normal molecule considered as zero. These results give two values of ${E}_{0}$, the electron affinity of the oxygen atom, both equal to 2.2\ifmmode\pm\else\textpm\fi{}0.2 v. The processes studied in CO are C${\mathrm{O}}^{\ensuremath{-}}$\ensuremath{\rightarrow}C+${\mathrm{O}}^{\ensuremath{-}}$ at 9.5 v, CO\ensuremath{\rightarrow}${\mathrm{C}}^{+}$+${\mathrm{O}}^{\ensuremath{-}}$ at 20.9 v, and C${\mathrm{O}}^{+}$\ensuremath{\rightarrow}${\mathrm{C}}^{+}$+O at 22.8 v, with an estimated accuracy of \ifmmode\pm\else\textpm\fi{}0.1 v. It is concluded that $D(\mathrm{CO})$ may have one of two possible values, 9.6\ifmmode\pm\else\textpm\fi{}0.1 or 11.6\ifmmode\pm\else\textpm\fi{}0.1 v. These experiments are unable to decide between the two but most of the evidence from other sources points to the lower value. If $D(\mathrm{CO})=9.6$ v we must admit the possibility of stable excited ${\mathrm{O}}^{\ensuremath{-}}$ ions. However, if $D(\mathrm{CO})=11.6$ v, these experiments on CO give two values of ${E}_{0}$, 1.9 and 2.1 v. The processes involved in the formation of negative ions by electron impact are discussed.