DECOMPOSITION MECHANISMS OF TRIMETHYLGALLIUM

The thermal decomposition of trimethylgallium (TMGa) has been studied in a variety of carrier gases, using a time-of-flight mass spectrometer to analyze the products and obtain kinetic information. N2 and He give almost identical pyrolysis curves. Addition of toluene in He shifts the decomposition to higher temperatures; thus methyl radical attack on the parent TMGa is important in the inert carriers. H2 and D2 accelerate the reaction compared to N2. Addition of a small amount of CH3 radicals from trimethylindium pyrolysis lowers the pyrolysis temperature significantly, indicating a chain reaction. The products of a D2/toluene mixture show that the active species are the H or D atoms rather than CH3 radicals. These data show that the major reactions involved in TMGa decomposition in N2 or He are (CH3)3Ga → CH3 + (CH3)2Ga and CH3 + (CH3)3Ga → CH4 + CH2Ga(CH3)2. In H2 a chain reaction takes place: CH3 + H2 → CH4 + H and H + (CH3)3Ga → CH4 + CH3 + CH3Ga. Numerical modeling was used to test these proposals. By this means it was determined that in addition to the reactions above, a key reaction is decomposition of CH2Ga(CH3)2 to give CH2GaCH3 + CH3. As with other main group organometallics, the entire decomposition mechanism is complex. © 1990.