K. Hirata, Y. Kobayashi, and Y. Ujihira
[J. Chem. Soc., Faraday Trans., Vol.93, No.1, pp.139-142, 1997]

The effect of halogenated compounds, p-dichlorobenzene (p-C₆H₄Cl₂), p-dibromobenzene (p-C₆H₄Br₂), and octafluoronaphthalene (C₁₀F₈), on positronium (Ps) formation in polycarbonate (PC) and polysulfone (PSF) has been studied by means of positron lifetime spectroscopy. The addition of the former two compounds to PC resulted in a reduction of the Ps yield, whereas the addition of the latter compound increased the Ps formation. The Ps formation, reduced by p-C₆H₄Cl₂, and p-C₆H₄Br₂, was found to be recovered on addition of C₁₀F₈. These results of inhibition, enhancement and anti-inhibition of Ps formation are successfully explained in terms of the spur reaction model of Ps formation. In contrast to the case of PC, the addition of the halogenated compounds to PSF did not have any effect on the Ps yield. It is suggested that the spur electrons are trapped on the -C₆H₄-SO₂-C₆H₄-group in PSF.