Mechanism of positronium formation in mixtures of fluorinated benzenes and n-Hexane

Positrinium yield (I₃) in binary mixturesof benzene derivatives(p-difluorobenzene 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, perfluorobenzene and p-xylene) in n-hexane has been measured. As additives all of the aromatic compounds have been found to enhance Ps yield in n-hexane, but the effect was unexpectedly smaller for 1,2,4,5-C₆H₂F₄. It is proposed that there are at least three processes which lead to the enhancement: anti-recombination by scavenging excess electrons, anti-recombination by scavenging positive holes, and electron abstraction from excited molecular states. Addition of a small amount of n-hexane in the fluorinated benzenes resultedin a decrease in the Ps yield to a different degree which strongly depended on the number of flourine atoms substituted. Discussion is made on the Ps formation mechanism taking into account possible role of excited molecular states.