CN– abstraction from cyano compounds by positrons

Abstract

The reactions of free positrons, e⁺, with (a) the cyano complexes of Cr^III, Fe^II, Fe^III, Co^III, Ni^II, Zn^II, Pt^II, Cd^II and Hg^II and (b) CH₃CN and CH₃CH₂CN have been investigated. The products of the reactions may be e⁺ adducts of the cyano compounds, e.g. [e⁺Co(CN)₆]^2–, or the e⁺CN^– positronide formed by CN^– abstraction. By means of the Doppler broadening of annihilation radiation lineshape, DBARL, spectroscopy it was found that positrons cause CN^– abstraction with all the reactants named above; and the full width at half-maximum (FWHM =Γ) of the DBARL component due to e⁺ annihilation in the e⁺X state is independent of the X substrate and equal to that of the e⁺CN^– compound formed in CN^– ion solutions. Therefore it was concluded that positrons interacting with cyano complexes and organic cyano derivatives cause CN^– abstraction and not the formation of e⁺ adducts. Finally a reasonable value for the first ionization potential, E_i, of CN^– ions was deduced from the correlation between E_i and Γ of e⁺X compounds with X = Cl^–, Br^– and I^–. The usefulness of this correlation as a diagnostic tool in the study of the e⁺ reactions is shown.