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

An apparatus previously described has been employed in a study of the dissociation produced by primary electron impact in CO and O₂. The processes studied in O₂ are O₂^-O^-+O at 2. 9 v and O₂^-O^-+O* at 12. 0 v with an estimated accuracy of 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 E₀, the electron affinity of the oxygen atom, both equal to 2. 20. 2 v. The processes studied in CO are CO^-+O^- at 9. 5 v, COC^++O^- at 20. 9 v, and CO^+C^++O at 22. 8 v, with an estimated accuracy of 0. 1 v. It is concluded that D (CO) may have one of two possible values, 9. 60. 1 or 11. 60. 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 (CO) =9. 6 v we must admit the possibility of stable excited O^- ions. However, if D (CO) =11. 6 v, these experiments on CO give two values of E₀, 1. 9 and 2. 1 v. The processes involved in the formation of negative ions by electron impact are discussed.