Probing intermediate process and active intermediate by positronium

A synthesis reaction of catalyst, olefin complex of rhodium,was chosen to explore the feasibility of probing active intermediate and intermediate process by positronium: Three different initial concentrations of ~h(111),7.6x10",3.8x10~~ and 4 . 5 ~ 1 0 ~ M were sampled. The relations between positronium lifetime intensity I, and the concentration of Rh(III),ethylene,as well as of the products were determined.The kobs of the reaction between positronium and Rh(II1) was obtained to be 4 .51~10~~I s ' . On the basis of the yield of product [(C2H4),RhC1], given in reference[l], the reaction rate constant was calculated to be O.152h-' for first-order reaction and 1.776h-' for second-order.Using these two constants and the measured relation between 7, and Rh(II1) concentration,according to the equations 1nC =InCo-k,t and 1IC = 1/C,+ k,,t, the theoretical relation between 7, and reaction time t for first-order and second-order reaction respectively were calculated. However, both the measured values of lifetime T, and intensity I, obviously departed from the calculated values, no matter it's first or second-order. The extra reduces of T, and I, were discussed and attributed to the presence of an active intermediate Rh(I1). In the light of the change tendency of T, with t, this synthesis process approximated to a second-order reaction. It showed that a dipolymer [(C,H4)(CH2-CH,-) RhCI,], might be formed in the first step of the synthesis. OH