WANG, YY (reprint author), ACAD SINICA CHINA,INST HIGH ENERGY PHYS,POB 2732,BEIJING 100080,PEOPLES R CHINA.
Article; Proceedings Paper
A synthesis reaction of catalyst, olefin complex of rhodium,was chosen to explore the feasibility of probing active intermediate and intermediate process by positronium: 2RhCl3.3H2O + 6C2H4 --> 2[(C2H4)2RhCl]2 + 4HCl + 2CH3CHO + 4H2O Three different initial concentrations of Rh(III), 7.6 x 10(-3), 3.8 x 10(-2) and 4.5 x 10(-2)M were sampled. The relations between positronium lifetime tau3, 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 4.51 x 10(9) M-1 s-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 tau3 and Rh(III) concentration, according to the equations lnC=lnC0-k(I)t and 1/C=1/C0+k(II)t, the theoretical relation between tau3 and reaction time t for first-order and second-order reaction respectively were calculated. However, both the measured values of lifetime tau3 and intensity I3 obviously departed from the calculated values, no matter it's first or second-order. The extra reduces of tau3 and I3 were discussed and attributed to the presence of an active intermediate Rh(II). In the light of the change tendency of tau3 with t, this synthesis process approximated to a second-order reaction. It showed that a dipolymer [GRAPHICS] RhCl2]2 might be formed in the first step of the synthesis.