High temperature shock-tube study of the reaction of gallium with ammonia

The gas-phase reaction of Ga atoms with NH3 was studied behind reflected shock waves in the temperature range of 1380 to 1870 K at pressures of 1.4 to 4.0 bar. Atomic-resonance-absorption spectroscopy (ARAS) at 403.299 nm was applied for the time-resolved determination of the Ga-atom concentration. Trimethylgallium (Ga(CH3)3) was used as a precursor of Ga atoms. After the initial increase in Ga concentration due to Ga(CH3)3 decomposition, the Ga concentration decreases rapidly in the presence of NH3. For the simulation of the measured Ga-atom concentration profiles from the studied reaction, additional knowledge about the thermal decomposition of Ga(CH3)3 is required. The rate coefficient k4 of the reaction Ga + NH3 → products (R4) was determined from the Ga-atom concentration profiles under pseudo-first-order assumption and found to be k4(T) = 1014.1±0.4 exp(−11 900 ± 700 K/T) cm3 mol−1 s−1 (error limits at the one standard deviation level). No significant pressure dependence was noticeable within the scatter of the data at the investigated pressure range.