CN– abstraction from cyano compounds by positrons
Abstract
The reactions of free positrons, e+, with (a) the cyano complexes of CrIII, FeII, FeIII, CoIII, NiII, ZnII, PtII, CdII and HgII 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, Ei, of CN– ions was deduced from the correlation between Ei 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.