The fully-optimized geometric structure, charge distribution and the fundamental vibrational frequencies as well as the energetics of the Me~3M/PH~3(Me=CH~3, M=Ga, In) systems are calculated by DFT method and the correspondent data for the Me~3Ga/NH~3 system are also calculated for comparison. It is shown that all the Me~3Ga·YH~3(Y=N, P) are stable adducts. Their formation reaction is exothermal. The M－ Y bond is fair weak in the Me~3M·YH~3 adducts,l but the bond is strengthened considerably after the adducts decompose into CH~4 and Me~2MYH~2 through an intra-molecular reaction. The possible pyrolysis paths of Me~3M are discussed based on the calculated results. Because the activation energy of the intra-molecular reaction should be much lower than that of direct breaking down a M－C bond in Me~3M, the pyrolysis reaction of Me~3M may most possibly proceeds through formation of intermediates Me~3M·YH~3 and Me~2MYH~2, when the YH~3 exists. This inference is in accordance with the existent experiment results. For example, the experiments show that when YH~3 exists, the decomposition temperature of Me~3M is lowered and the decomposition of Me~3M and YH~3 is synchronous with the production of CH~4. The products Me~2MPH~2 can react further, e.g. the lone pair on P can be donated to the M atom in a MP surface, facilitating the further release of CH~4 and forming a MP film. This inference is in accordance with the fact that the MP surface catalyzes the deposition reaction in the Me~3In/PH~3 system.

Key words: ORGANOMETALLIC COMPOUNDS, VAPOR PHASE DEPOSITION, MOLECULAR STRUCTURE