Abstract Positronium (Ps) yields were measured for CS 2/THF, CS 2/TEA, C 6F 6 THF and C 6F 6/TEA mixtures. Addition of C 6F 6 or CS 2 into TEA or THF showed a similar influence which induces a decrease of Ps yield. This is ascribed to the non-dissociative electron scavenging by both CS 2 and C 6F 6. On the other hand, the effect of addition of TEA and THF has been found to be different for C 6F 6 and CS 2, i.e. both TEA and THF did not change Ps yield in CS 2 substantially, while they caused a sharp decrease of Ps yield in C 6F 6. The latter sharp decreases was ascribed to quenching of excited state of C 6F 6. This interpretation is supported by pulse radiolysis emission measurements for the same system, in which it was found that TEA quenches the excited state of C 6F 6 efficiently.