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

Abstract

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) = 10^14.1±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.