Probing intermediate process and active intermediate by positronium

Abstract
A synthesis reaction of catalyst, olefin complex of rhodium,was chosen to explore the feasibility of probing active intermediate and intermediate process by positronium : 2RhCl₃3H₂O + 6C₂H₄ → 2[(C₂H₄)₂RhCl]₂ + 4HCl + 2CH₃CHO + 4H₂O Three different initial concentrations of Rh(III), 7.6x10^-3, 3.8x10^-2 and 4.5x10^-2M were sampled. The relations between positronium lifetime [MATH]₃, intensity I₃ and the concentration of Rh(III), ethylene, as well as of the products were determined. The k_obs of the reaction between positronium and Rh(III) was obtained to be 4.51x10⁹M^-1s^-1. On the basis of the yield of product [(C₂H₄)₂RhCl]₂ given in reference[1], the reaction rate constant was calculated to be 0.152h^-1 for first-order reaction and 1.776h^-1 for second-order. Using these two constants and the measured relation between τ₃ and Rh(III) concentration, according to the equations lnC=lnC₀-k_It and 1/C = 1/C₀+ k_IIt, the theoretical relation between τ₃ and reaction time t for first-order and second-order reaction respectively were calculated. However, both the measured values of lifetime τ₃ and intensity I₃ obviously departed from the calculated values, no matter it's first or second-order. The extra reduces of τ₃ and I₃ were discussed and attributed to the presence of an active intermediate Rh(II). In the light of the change tendency of τ₃ with t, this synthesis process approximated to a second-order reaction. It showed that a dipolymer [(C₂H₄)([MATH]-CH₂-) RhCl₂]₂ might be formed in the first step of the synthesis.