Density functional study on the systems (CH3)3M/PH3(M = Ga, In)

The fully - optimized geometric structure, charge distribution and the fundamental vibrational frequencies as well as the energetics of the Me3M/PH3(Me = CH3, M = Ga, In) systems are calculated by DFT method and the correspondent data for the Me3Ga/NH3 system are also calculated for comparison. It is shown that all the Me3M . YH3(Y = N, P) are stable adducts. Their formation reaction is exothermal. The M I bond is fair weak in the Me3M . YH3 adducts, but the bond is strengthened considerably after the adducts decompose into CH4 and Me2MYH2 through an intra - molecular reaction. The possible pyrolysis paths of Me3M 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 Me3M, the pyrolysis reaction of Me3M may most possibly proceeds through formation of intermediates Me3M . YH3 and Me2MYH2, when the YH3 exists. This inference is in accordance with the existent experiment results. For example, the experiments show that when YH3 exists, the decomposition temperature of Me3M is lowered and the decomposition of Me3M and YH3 is synchronous with the production of CH4. The products Me2MPH2 can react further, e.g. the lone pair an P can be donated to the M. atom in a RIP surface, facilitating the further release of CH4 and forming a MP film. This inference is in accordance with the fact that the MP surface catalyzes the deposition reaction in the Me3In/PH3 system.