Abstract: The mechanism of singlet germylene and formaldehyde's cycloaddition reaction heve been studied by using ab initio method. We obtained the intermediate complex and transition state of this reaction, and then discussed the mechanism of the reaction. On the basis of ab initio and with the statistical thermodynamics method and transition-state theory we have calculated the reaction's change of thermodynamic functions and the quality of kinetic properties at different temperatures. The results show this reaction proceeds with two steps: (1) germylene and formaldehyde form an intermediate complex, which is a kind of exothermal reaction with no barrier; (2) the isomerized intermediate complex becomes the product, which after being corrected by zero-point energies, the barrier of reaction is 69.6 kJ/mol(MP2/3-21G//3-21G). On account for dynamics and thermodynamies, it is found that the reaction will not only have the larger sponlaneous tendency and equilibrum constants, but also the quicker reaction rate in the range of 400 K～500 K.

Key words: Germylene, Cycloaddition reaction, Ab initio calculation, Thermodynamic and kinetic properties