ABSOLUTE RATE CONSTANTS FOR THE REACTION OF CN WITH CH4, C2H6, AND C3H8 FROM 292-K TO 1500-K USING HIGH-TEMPERATURE PHOTOCHEMISTRY AND DIODE-LASER ABSORPTION

By combining the laser-induced fluorescence detection technique with high-temperature reactor technology, absolute rate constants for the reaction of CN with CH4, C2H6, and C3H8 have been measured as a function of temperature (292-1500 K) and pressure (5-60 Torr). CN radicals were generated by 193-nm excimer laser photolysis of dilute C2N2/Ar mixtures. Radical decays were monitored by laser-induced fluorescence from the B2-SIGMA+ <-- X2-SIGMA+ transition near 387 nm under pseudo-first-order conditions. Arrhenius plots of the rate constants show significant curvature. The temperature-dependent rate constants have been fit to modified Arrhenius expressions of the form k = AT(n) exp(-E/T). This study represents the widest continuous temperature range over which rate constants for these reactions have been measured directly. The reaction kinetics and products of these reactions were also studied at 295 K by diode laser absorption. Rate constants obtained from product growth are in good agreement with the laser-induced fluorescence data. For these reactions at 295 K, HCN was found to be the dominant observable product.