Positronium annihilation in fluorinated benzene derivatives

Positron lifetime measurements have been carried out to study formation and annihilation of ortho-positronium (o-Ps) in a series of fluorinated benzene derivatives. The o-Ps lifetimes (τ3) are longer than those expected from Tao's empirical relationship for hydrocarbons, τ3-1 (ns-1) = 0.061σ0.5, where σ is the surface tension of the liquids in units of mN m-1. It was found that there is a rather good correlation between the o-Ps intensity I3 and the dipole moment for the fluorinated compounds. (author)