Mass-spectrometric tracer and photometric studies of catalysed radical recombination in flames

Abstract

Measurements of hydrogen atom concentrations in H₂+ O₂+ N₂ flames with and without additives have been made by a mass-spectrometric tracer method dependent upon the reaction Sr⁺+ H₂O ⇌ SrOH⁺+ H, K= 47 exp(–7 700 K/T), being balanced and by a well established photometric method dependent upon balance of the analogous reaction Li + H₂O ⇌ LiOH + H, K= 16 exp(–10 000 K/T). Results from the two methods agree well. Catalysis of flame radical recombination caused by addition of tin, molybdenum and tungsten is described. Mass-spectrometric results for tin are in good agreement with previous photometric measurements. Results for molybdenum and tungsten from both methods are quantitatively interpreted in terms of a cyclic homogeneous gas phase mechanism, with associated thermochemistry and reaction rate coefficients.