The mechanism of the cycloaddition reaction of singlet germylene with ethylene has been studied by RHF/6-31G^* gradient method. The electron correlation energies of all the structures are calculated by using second-order Moller-Plesset perturbation theory (MP2). We have also calculated the changes of thermodynamic functions and the quality of kinetic properties for this reaction at different temperatures by using statistical thermodynamics method and transition state theory. The results show that this reaction proceeds in two steps: (1)germylene and ethylene form an intermediate complex through a kind of exothermal reaction without any barrier; (2)the intermediate complex isomterized to give the product, after being corrected for the zero point energies, the barrier is 26.9kJ.mol^-^1 (MP2/6-31G^*//6-31G^*). In view of dynamics and thermodynamics, it is between 200-300K that the reaction will have not only the larger spontaneous tendency and equilibrium constant but also higher reaction rate.

Key words: ETHYLENE, CYCLOADDITION REACTION, AB INITIO CALCULATION, TRANSITION STATE THEORY