Ortho-Positronium Annihilation in Room Temperature Ionic Liquids

Very new phenomena have been found in room temperature ionic liquids, e.g. oscillation of positronium (Ps) bubble. It is almost impossible to see this kind of phenomenon in usual molecular liquids. The Ps bubble oscillations in N,N,N-trimethyl-N-propylammonium bis(trifluoro-methanesulfonyl)imide (TMPA-TFSI), N-methyl-N-propylpiperidinium bis(trifluoromethane-sulfonyl) imide (PP13-TFSI) and 1-ethyl-3-methylimidazolium thiocyanate (EMIM-SCN) were successfully observed. Even though the Ps bubble size is smaller for EMIM-SCN, the oscillation frequency of the Ps bubble at 10°C above the melting temperatures was quite similar for the other room temperature ionic liquids. Hence, the Ps bubble oscillation is, probably, caused by the repulsive force initiated by the ionic structures in room temperature ionic liquids that can remain at 10-15°C above the melting temperatures.