A SHOCK-TUBE STUDY OF REACTIONS OF CN WITH HCN, OH, AND H-2 USING CN AND OH LASER-ABSORPTION

Quantitative, narrow-line laser absorption measurements of CN time-his tories at 388.444 nm were acquired in high-temperature pyrolysis and l aser photolysis shock tube experiments. The data were analyzed using a detailed kinetics mechanism to determine the rate coefficients of the reactions CN + OH --> Products (1) CN + HCN --> C2N2 + H (2) CN + H-2 --> HCN + H (3) for temperatures between 940 and 1860 K. Two independ ent experimental approaches were utilized: laser photolysis (at 193 nm ) of dilute C2N2/HCN/argon and C2N2/H-2/argon mixtures in reflected sh ock wave experiments, and shock heating of HNO3/HCN/argon mixtures in incident and reflected shock wave experiments. Laser absorption measur ements of OH at 306.687 nm were also taken in the HNO3/HCN/argon exper iments. The results are in good agreement with rate coefficient determ inations from previous studies at different temperatures. The expressi on k(2) = 1.51 X 10(7) T-1.71 exp(-770/T) cm(3) mol(-1) s(-1) (f = 0.8 5, F = 1.15), derived by Yang et al. (1992) from their k(2) measuremen ts in combination with those of Szekely et al. (1983), is recommended for the broad temperature range 300-3000 K, The uncertainty factors f and F give the limiting values of the rate coefficient: k(min) = f(bes t fit), k(max) = Fk(best fit). The recommended expression for the rate coefficient of reaction (3) k(3) = 2.95 X 10(5) T-2.45 exp(-1126/T) c m(3) mol(-1) s(-1) (f = 0.83, F = 1.22), also valid for temperatures 3 00-1000 K, is taken from the transition state theory analysis of the C N + H-2 reaction by Wagner and Bair (1986). The rate coefficient for r eaction (1) was measured to be 4.0 X 10(13) cm(3) mol(-1) s(-1) (f = 0 .61, F = 1.40) For the temperature range 1250-1860 K. (C) 1996 John Wi ley & Sons, Inc.