OXIDATION OF S AND SO BY O-2 IN HIGH-TEMPERATURE PYROLYSIS AND PHOTOLYSIS REACTION SYSTEMS

The reaction of S atoms with O-2 was studied behind reflected shock wa ves applying atomic resonance absorption spectroscopy (ARAS) for conce ntration measurements of S and O atoms. S atoms were generated either by laser-flash photolysis (LFP) of CS2 or by the high-temperature pyro lysis of COS, respectively. The concentrations of Oz in the mixtures r anged between 50 ppm and 400 ppm, and those of the S precursors, CS2 a nd COS, between 5 and 25 ppm. The rate coefficient of the reaction [GR APHICS] was determined from the observed decay of the S absorption sig nals for temperatures 1220 K less than or equal to T less than or equa l to 3460 K. The measured O-atom concentration profiles in COS/O-2/Ar reaction systems were evaluated, using simplified kinetic mechanism, t o verify the given rate coefficient ks. In experiments with the highes t value of the [O-2]/[COS] ratio the measured O-atom concentrations we re found to be sensitive to the reaction: [GRAPHICS] The fitting of th e calculated O-atom profiles to the measured ones results in mean valu e of: k(6) = 8.0 X 10(11) cm(3) mol(-1) s(-1). which is to be valid fo r the temperature range 2570 K less than or equal to T less than or eq ual to 2980 K. A first-order analysis of the observed S absorption dec ay in LFP shock wave experiments on CS2/Ar gas mixtures resulted in a rate coefficient of the background reaction (R4): [GRAPHICS] for tempe ratures 1260 K less than or equal to T less than or equal to 1820 K. ( C) 1995 John Wiley & Sons, Inc.