An attempt to apply ligand field theory to positronium reactions with 3d complexes

Abstract

Positronium, Ps, the bound state between an electron, e, and a positron, c+, may have two spin states: theortho,o-Ps, and thepara,p-Ps, states, which differ for the spin orientation of the two particles. The two types of Ps atoms may be inter-converted by collision with paramagnetic compounds, such as several3d complexes. By investigating about 90 complexes of VII, CrII, CrIII, MnII, FeII, CoII and NiII as a function of temperature, it was found that the rate constants kCR of theo-Ps intop-Ps conversion reactions, CR, are linearly correlated to the delocalization β of metal electrons caused by the ligands. Therefore, if β known, kCR may be estimated andvice versa. This suggests a new method for the experimental determination of β. The rate constants of the Ps oxidation reactions by CoIII complexes were also investigated and discussed. The paper is preceded by four sections dealing with: 1) the positron and positronium formation; 2) the positron annihilation modes; 3) the methods for measuring the Ps rate constants and establishing the Ps reaction types; 4) the application of the Smoluchowski equation to Ps reactions. Moreover, an attempt is made to ascertain the standard electrochemical potential of Ps atoms. The positron reactions and the formation of positronides are also taken into consideration.