Positronium interactions in organic solvents

In the present work, the chemistry of the positronium (Ps) species has been investigated in pure benzene, pyridine and their mixtures with pyridine concentrations at 4.12, 6.18 and 8.24 M, respectively, using the Doppler-broadened line-shape analysis technique. It is seen that the intensities of the para-(p-Ps) and ortho-Ps (o-Ps) in benzene and that of p-Ps in pyridine follow the Ore-model predictions while the intensity of o-Ps in pyridine is much lower than expected from this model. On the basis of these observations and of decrease in the o-Ps lifetime with increasing pyridine concentration in various organic solvents as reported in literature, it is concluded that pick-off is not the only quenching mechanism for Ps in organic solvents and pyridine is a quencher of Ps-species rather than an inhibitor. Calculations carried out considering a diffusion-controlled mechanism of Ps-quenching in pyridine via unstable (dissociative) complex/adduct formation and the bubble model show that the quenching rate is diffusion controlled and the pick-off rate is in accordance with the free-volume model. These conclusions were confirmed in the mixtures of benzene and pyridine.