Positronium bubble oscillation in room temperature ionic liquids-Temperature dependence

Abstract

The temperature dependent oscillation of the ortho-positronium pick-off annihilation rate was successfully observed for a room temperature ionic liquid (IL), N,N,N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl)imide (TMPA-TFSI). The fundamental frequencies at 25C and 30C were 5.85GHz and 4.00GHz, respectively. The decay of the oscillation was faster at higher temperature, 30C. Moreover, the higher harmonic frequencies could explain the change of ortho-positronium pick-off annihilation rate successfully. The macroscopic viscosity of the IL could not explain the appearance of the oscillation. It indicated that the positron annihilation methods were very strong tools to study the properties of IL's in sub-nanometer scale that must be very different from the macroscopic properties.