Further studies of the spur process of positronium formation in mixtures of organic liquids

To test some predictions of the spur model of positronium (Ps) formation, positron lifetime studies were made of the following binary organic mixtures: (a) carbondisulphide mixtures with n-tetradecane, n-hexane, isooctane, neopentane, and tetramethylsilane (TMS); (b) neopentane mixtures with methanol, ethanol, cyclohexanol, and methylcyclohexane; (c) cis-2-butene/trans-2-butene, and benzene/ethanol. The results were in agreement with the model. A minimum in the Ps yield versus CS₂ concentration, explained as being caused by electron localization on CS₂ at low and delocalization on several CS₂ molecules at higher CS₂ concentration, depended on the electron work function V_o of the solvent. This minimum was pronounced (shallow or absent) at high (low) V_o. Solvation of electrons and positrons in alcohol clusters strongly influenced the Ps yield for the neopentane mixtures. The Ps yield was higher in cis- than in trans-2-butene. The Ps formation process in polar liquids is discussed. Experiment facts do not preclude that Ps is also formed by the encounter pair process of fully solvated particles in the positron spur.