J. Phys. IV France 03 (1993) C4-99-C4-104
Probing intermediate process and active intermediate by positroniumY.Y. WANG, H.M. CAO and Y.H. GUO
Institute of High Energy Physics, Academia Sinica of China, P.O. Box 2732, Beijing 100080, China
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 kobs 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, 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-kIt and 1/C = 1/C0+ kIIt, 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.
© EDP Sciences 1993