Under examination of the probability of ortho-positronium formation (I,3,) in some binary systems containing CS,2, or C,6,F,6, it is found that the competitive reaction mechanism in spur may be changed as a result of additives. The additive CS,2, can increase the relative rate of recombination reaction of active cation-electron in competitive process, and the reaction rate constant of Ps formation in C,6,F,6, is much larger than that in C,6,H,5,Cl (by a factor of 60). A "resonant recombination reaction" mechanism possibly occured in the spur is advanced, and a potential relativity schematic drawing deciding whether the resonant recombination reaction can occur or not is proposed. Consequently, an eloquent and direct proof of "resonant recombination reaction" mechanism is given.