Temperature dependence of the inhibition of positronium by chlorine-substituted hydrocarbons in non-polar liquids

Abstract

Abstract Positron annihilation lifetime spectra were measured for solutions of 1,2,3,5-C 6 H 2 Cl 4 in hexane, toluene, m -xylene and mesitylene, CCl 4 in hexane and toluene, and C 2 HCl 3 in n -hexane for concentrations below 1 M and at various temperatures between −30°C and 67°C. The Ps inhibition by C 6 H 2 Cl 4 was roughly 14 times stronger at −30°C than at 67°C in toluene, m -xylene, and mesitylene, while that of CCl 4 displayed hardly any temperature dependence in hexane and toluene. Previously, the Ps inhibition by C 6 H 2 Cl 4 in various liquids at 20°C was explained by a competition between electron pick off by the positron from C 6 H 2 Cl 4 − formed by electron scavenging in the positron spur, and dehalogenation of the same anion at picosecond times after the spur formation. Three effects might reasonably explain the strong temperature dependence of the Ps inhibition of C 6 H 2 Cl 4 : (1) The dechlorination time of C 6 H 2 Cl 4 − might be much shorter at low than at high temperatures. (2) The positron mobility might decrease very strongly with decreasing temperature. (3) Positrons possibly trapped on C 6 H 2 Cl 4 might thermally detach at high but not at low temperatures.