Positronium in room temperature ionic liquids

Hirade, Tetsuya  

Ps has a negative work function in insulating materials and the repulsion between Ps and surrounding molecules can form a bubble in liquids. It is needed to lose energy to have a stable bubble state. The Ps bubble stabilizes within about 10 ps in usual liquids, but not in room temperature ionic liquids (IL). It would take about 1 ns in TMPA-TFSI. The ortho-Ps pick off annihilation probability depends on the size of the Ps bubble and hence the change of the ortho-Ps pick-off annihilation rate caused by the change of the bubble size on the lifetime spectra was expected. The results obtained from the lifetime spectra for TMPA-TFSI indicate that the Ps bubble oscillates in IL before the Ps bubble stabilization. On the other hand, the ortho-Ps pick-off annihilation rate obtained at older positron age region showed smaller annihilation rates than the expected one with the surface tension of IL. Positron annihilation methods will be a very strong tool to investigate the structure of IL.