Temperature and (polar) solvent effects on positron reactions and positronium formation in iodide solutions

Abstract

Abstract The influence of solvent and of temperature on the reactions of positrons and on the formation of positronium (Ps) is investigated in solutions of iodide in water, methanol, glycol, a 40–60 mole% glycerol—water mixture and in 1,3-propanediol. Life time spectroscopy and the Doppler broadening of annihilation radiation line shape technique are used in conjunction to better assess the positron reactions. Saturation effects in the (e + I − ) bound-state intensity at high I − concentration are confirmed and can be explained by supposing the unstability of this complex. The temperature effects on (e + I − ) and Ps formation range from weak (water) to strong (glycol) and indicate the reaction of positrons associated with the fluid. In the polyalcohols, the shape of the Ps yield versus I − concentration curves is not consistent with a model previously proposed and implying delocalization of e + . Assuming that the enhancement of the Ps yield in water and in methanol arises from the reaction of I − with the positive holes, the results for the polyalcohols would indicate a much lower mobility of the holes than in water or in methanol, ascribed to the efficient trapping by the neighbouring OH groups.